java/util/Properties.java

/*
 * Copyright (c) 1995, 2017, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.util;

import java.io.IOException;
import java.io.PrintStream;
import java.io.PrintWriter;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.Reader;
import java.io.Writer;
import java.io.OutputStreamWriter;
import java.io.BufferedWriter;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.StreamCorruptedException;
import java.io.UnsupportedEncodingException;
import java.nio.charset.Charset;
import java.nio.charset.IllegalCharsetNameException;
import java.nio.charset.UnsupportedCharsetException;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.BiConsumer;
import java.util.function.BiFunction;
import java.util.function.Function;

import jdk.internal.misc.SharedSecrets;
import jdk.internal.misc.Unsafe;
import jdk.internal.util.xml.PropertiesDefaultHandler;

import sun.nio.cs.UTF_8;
import sun.nio.cs.ISO_8859_1;

/**
 * The {@code Properties} class represents a persistent set of
 * properties. The {@code Properties} can be saved to a stream
 * or loaded from a stream. Each key and its corresponding value in
 * the property list is a string.
 * <p>
 * A property list can contain another property list as its
 * "defaults"; this second property list is searched if
 * the property key is not found in the original property list.
 * <p>
 * Because {@code Properties} inherits from {@code Hashtable}, the
 * {@code put} and {@code putAll} methods can be applied to a
 * {@code Properties} object.  Their use is strongly discouraged as they
 * allow the caller to insert entries whose keys or values are not
 * {@code Strings}.  The {@code setProperty} method should be used
 * instead.  If the {@code store} or {@code save} method is called
 * on a "compromised" {@code Properties} object that contains a
 * non-{@code String} key or value, the call will fail. Similarly,
 * the call to the {@code propertyNames} or {@code list} method
 * will fail if it is called on a "compromised" {@code Properties}
 * object that contains a non-{@code String} key.
 *
 * <p>
 * The iterators returned by the {@code iterator} method of this class's
 * "collection views" (that is, {@code entrySet()}, {@code keySet()}, and
 * {@code values()}) may not fail-fast (unlike the Hashtable implementation).
 * These iterators are guaranteed to traverse elements as they existed upon
 * construction exactly once, and may (but are not guaranteed to) reflect any
 * modifications subsequent to construction.
 * <p>
 * The {@link #load(java.io.Reader) load(Reader)} {@code /}
 * {@link #store(java.io.Writer, java.lang.String) store(Writer, String)}
 * methods load and store properties from and to a character based stream
 * in a simple line-oriented format specified below.
 *
 * The {@link #load(java.io.InputStream) load(InputStream)} {@code /}
 * {@link #store(java.io.OutputStream, java.lang.String) store(OutputStream, String)}
 * methods work the same way as the load(Reader)/store(Writer, String) pair, except
 * the input/output stream is encoded in ISO 8859-1 character encoding.
 * Characters that cannot be directly represented in this encoding can be written using
 * Unicode escapes as defined in section 3.3 of
 * <cite>The Java&trade; Language Specification</cite>;
 * only a single 'u' character is allowed in an escape
 * sequence.
 *
 * <p> The {@link #loadFromXML(InputStream)} and {@link
 * #storeToXML(OutputStream, String, String)} methods load and store properties
 * in a simple XML format.  By default the UTF-8 character encoding is used,
 * however a specific encoding may be specified if required. Implementations
 * are required to support UTF-8 and UTF-16 and may support other encodings.
 * An XML properties document has the following DOCTYPE declaration:
 *
 * <pre>
 * &lt;!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd"&gt;
 * </pre>
 * Note that the system URI (http://java.sun.com/dtd/properties.dtd) is
 * <i>not</i> accessed when exporting or importing properties; it merely
 * serves as a string to uniquely identify the DTD, which is:
 * <pre>
 *    &lt;?xml version="1.0" encoding="UTF-8"?&gt;
 *
 *    &lt;!-- DTD for properties --&gt;
 *
 *    &lt;!ELEMENT properties ( comment?, entry* ) &gt;
 *
 *    &lt;!ATTLIST properties version CDATA #FIXED "1.0"&gt;
 *
 *    &lt;!ELEMENT comment (#PCDATA) &gt;
 *
 *    &lt;!ELEMENT entry (#PCDATA) &gt;
 *
 *    &lt;!ATTLIST entry key CDATA #REQUIRED&gt;
 * </pre>
 *
 * <p>This class is thread-safe: multiple threads can share a single
 * {@code Properties} object without the need for external synchronization.
 *
 * @apiNote
 * The {@code Properties} class does not inherit the concept of a load factor
 * from its superclass, {@code Hashtable}.
 *
 * @author  Arthur van Hoff
 * @author  Michael McCloskey
 * @author  Xueming Shen
 * @since   1.0
 */
public
class Properties extends Hashtable<Object,Object> {
    /**
     * use serialVersionUID from JDK 1.1.X for interoperability
     */
    private static final long serialVersionUID = 4112578634029874840L;

    private static final Unsafe UNSAFE = Unsafe.getUnsafe();

    /**
     * A property list that contains default values for any keys not
     * found in this property list.
     *
     * @serial
     */
    protected volatile Properties defaults;

    /**
     * Properties does not store values in its inherited Hashtable, but instead
     * in an internal ConcurrentHashMap.  Synchronization is omitted from
     * simple read operations.  Writes and bulk operations remain synchronized,
     * as in Hashtable.
     */
    private transient volatile ConcurrentHashMap<Object, Object> map;

    /**
     * Creates an empty property list with no default values.
     *
     * @implNote The initial capacity of a {@code Properties} object created
     * with this constructor is unspecified.
     */
    public Properties() {
        this(null, 8);
    }

    /**
     * Creates an empty property list with no default values, and with an
     * initial size accommodating the specified number of elements without the
     * need to dynamically resize.
     *
     * @param  initialCapacity the {@code Properties} will be sized to
     *         accommodate this many elements
     * @throws IllegalArgumentException if the initial capacity is less than
     *         zero.
     */
    public Properties(int initialCapacity) {
        this(null, initialCapacity);
    }

    /**
     * Creates an empty property list with the specified defaults.
     *
     * @implNote The initial capacity of a {@code Properties} object created
     * with this constructor is unspecified.
     *
     * @param   defaults   the defaults.
     */
    public Properties(Properties defaults) {
        this(defaults, 8);
    }

    private Properties(Properties defaults, int initialCapacity) {
        // use package-private constructor to
        // initialize unused fields with dummy values
        super((Void) null);
        map = new ConcurrentHashMap<>(initialCapacity);
        this.defaults = defaults;

        // Ensure writes can't be reordered
        UNSAFE.storeFence();
    }

    /**
     * Calls the {@code Hashtable} method {@code put}. Provided for
     * parallelism with the {@code getProperty} method. Enforces use of
     * strings for property keys and values. The value returned is the
     * result of the {@code Hashtable} call to {@code put}.
     *
     * @param key the key to be placed into this property list.
     * @param value the value corresponding to {@code key}.
     * @return     the previous value of the specified key in this property
     *             list, or {@code null} if it did not have one.
     * @see #getProperty
     * @since    1.2
     */
    public synchronized Object setProperty(String key, String value) {
        return put(key, value);
    }


    /**
     * Reads a property list (key and element pairs) from the input
     * character stream in a simple line-oriented format.
     * <p>
     * Properties are processed in terms of lines. There are two
     * kinds of line, <i>natural lines</i> and <i>logical lines</i>.
     * A natural line is defined as a line of
     * characters that is terminated either by a set of line terminator
     * characters ({@code \n} or {@code \r} or {@code \r\n})
     * or by the end of the stream. A natural line may be either a blank line,
     * a comment line, or hold all or some of a key-element pair. A logical
     * line holds all the data of a key-element pair, which may be spread
     * out across several adjacent natural lines by escaping
     * the line terminator sequence with a backslash character
     * {@code \}.  Note that a comment line cannot be extended
     * in this manner; every natural line that is a comment must have
     * its own comment indicator, as described below. Lines are read from
     * input until the end of the stream is reached.
     *
     * <p>
     * A natural line that contains only white space characters is
     * considered blank and is ignored.  A comment line has an ASCII
     * {@code '#'} or {@code '!'} as its first non-white
     * space character; comment lines are also ignored and do not
     * encode key-element information.  In addition to line
     * terminators, this format considers the characters space
     * ({@code ' '}, {@code '\u005Cu0020'}), tab
     * ({@code '\t'}, {@code '\u005Cu0009'}), and form feed
     * ({@code '\f'}, {@code '\u005Cu000C'}) to be white
     * space.
     *
     * <p>
     * If a logical line is spread across several natural lines, the
     * backslash escaping the line terminator sequence, the line
     * terminator sequence, and any white space at the start of the
     * following line have no affect on the key or element values.
     * The remainder of the discussion of key and element parsing
     * (when loading) will assume all the characters constituting
     * the key and element appear on a single natural line after
     * line continuation characters have been removed.  Note that
     * it is <i>not</i> sufficient to only examine the character
     * preceding a line terminator sequence to decide if the line
     * terminator is escaped; there must be an odd number of
     * contiguous backslashes for the line terminator to be escaped.
     * Since the input is processed from left to right, a
     * non-zero even number of 2<i>n</i> contiguous backslashes
     * before a line terminator (or elsewhere) encodes <i>n</i>
     * backslashes after escape processing.
     *
     * <p>
     * The key contains all of the characters in the line starting
     * with the first non-white space character and up to, but not
     * including, the first unescaped {@code '='},
     * {@code ':'}, or white space character other than a line
     * terminator. All of these key termination characters may be
     * included in the key by escaping them with a preceding backslash
     * character; for example,<p>
     *
     * {@code \:\=}<p>
     *
     * would be the two-character key {@code ":="}.  Line
     * terminator characters can be included using {@code \r} and
     * {@code \n} escape sequences.  Any white space after the
     * key is skipped; if the first non-white space character after
     * the key is {@code '='} or {@code ':'}, then it is
     * ignored and any white space characters after it are also
     * skipped.  All remaining characters on the line become part of
     * the associated element string; if there are no remaining
     * characters, the element is the empty string
     * {@code ""}.  Once the raw character sequences
     * constituting the key and element are identified, escape
     * processing is performed as described above.
     *
     * <p>
     * As an example, each of the following three lines specifies the key
     * {@code "Truth"} and the associated element value
     * {@code "Beauty"}:
     * <pre>
     * Truth = Beauty
     *  Truth:Beauty
     * Truth                    :Beauty
     * </pre>
     * As another example, the following three lines specify a single
     * property:
     * <pre>
     * fruits                           apple, banana, pear, \
     *                                  cantaloupe, watermelon, \
     *                                  kiwi, mango
     * </pre>
     * The key is {@code "fruits"} and the associated element is:
     * <pre>"apple, banana, pear, cantaloupe, watermelon, kiwi, mango"</pre>
     * Note that a space appears before each {@code \} so that a space
     * will appear after each comma in the final result; the {@code \},
     * line terminator, and leading white space on the continuation line are
     * merely discarded and are <i>not</i> replaced by one or more other
     * characters.
     * <p>
     * As a third example, the line:
     * <pre>cheeses
     * </pre>
     * specifies that the key is {@code "cheeses"} and the associated
     * element is the empty string {@code ""}.
     * <p>
     * <a id="unicodeescapes"></a>
     * Characters in keys and elements can be represented in escape
     * sequences similar to those used for character and string literals
     * (see sections 3.3 and 3.10.6 of
     * <cite>The Java&trade; Language Specification</cite>).
     *
     * The differences from the character escape sequences and Unicode
     * escapes used for characters and strings are:
     *
     * <ul>
     * <li> Octal escapes are not recognized.
     *
     * <li> The character sequence {@code \b} does <i>not</i>
     * represent a backspace character.
     *
     * <li> The method does not treat a backslash character,
     * {@code \}, before a non-valid escape character as an
     * error; the backslash is silently dropped.  For example, in a
     * Java string the sequence {@code "\z"} would cause a
     * compile time error.  In contrast, this method silently drops
     * the backslash.  Therefore, this method treats the two character
     * sequence {@code "\b"} as equivalent to the single
     * character {@code 'b'}.
     *
     * <li> Escapes are not necessary for single and double quotes;
     * however, by the rule above, single and double quote characters
     * preceded by a backslash still yield single and double quote
     * characters, respectively.
     *
     * <li> Only a single 'u' character is allowed in a Unicode escape
     * sequence.
     *
     * </ul>
     * <p>
     * The specified stream remains open after this method returns.
     *
     * @param   reader   the input character stream.
     * @throws  IOException  if an error occurred when reading from the
     *          input stream.
     * @throws  IllegalArgumentException if a malformed Unicode escape
     *          appears in the input.
     * @throws  NullPointerException if {@code reader} is null.
     * @since   1.6
     */
    public synchronized void load(Reader reader) throws IOException {
        Objects.requireNonNull(reader, "reader parameter is null");
        load0(new LineReader(reader));
    }

    /**
     * Reads a property list (key and element pairs) from the input
     * byte stream. The input stream is in a simple line-oriented
     * format as specified in
     * {@link #load(java.io.Reader) load(Reader)} and is assumed to use
     * the ISO 8859-1 character encoding; that is each byte is one Latin1
     * character. Characters not in Latin1, and certain special characters,
     * are represented in keys and elements using Unicode escapes as defined in
     * section 3.3 of
     * <cite>The Java&trade; Language Specification</cite>.
     * <p>
     * The specified stream remains open after this method returns.
     *
     * @param      inStream   the input stream.
     * @exception  IOException  if an error occurred when reading from the
     *             input stream.
     * @throws     IllegalArgumentException if the input stream contains a
     *             malformed Unicode escape sequence.
     * @throws     NullPointerException if {@code inStream} is null.
     * @since 1.2
     */
    public synchronized void load(InputStream inStream) throws IOException {
        Objects.requireNonNull(inStream, "inStream parameter is null");
        load0(new LineReader(inStream));
    }

    private void load0(LineReader lr) throws IOException {
        StringBuilder outBuffer = new StringBuilder();
        int limit;
        int keyLen;
        int valueStart;
        boolean hasSep;
        boolean precedingBackslash;

        while ((limit = lr.readLine()) >= 0) {
            keyLen = 0;
            valueStart = limit;
            hasSep = false;

            //System.out.println("line=<" + new String(lineBuf, 0, limit) + ">");
            precedingBackslash = false;
            while (keyLen < limit) {
                char c = lr.lineBuf[keyLen];
                //need check if escaped.
                if ((c == '=' ||  c == ':') && !precedingBackslash) {
                    valueStart = keyLen + 1;
                    hasSep = true;
                    break;
                } else if ((c == ' ' || c == '\t' ||  c == '\f') && !precedingBackslash) {
                    valueStart = keyLen + 1;
                    break;
                }
                if (c == '\\') {
                    precedingBackslash = !precedingBackslash;
                } else {
                    precedingBackslash = false;
                }
                keyLen++;
            }
            while (valueStart < limit) {
                char c = lr.lineBuf[valueStart];
                if (c != ' ' && c != '\t' &&  c != '\f') {
                    if (!hasSep && (c == '=' ||  c == ':')) {
                        hasSep = true;
                    } else {
                        break;
                    }
                }
                valueStart++;
            }
            String key = loadConvert(lr.lineBuf, 0, keyLen, outBuffer);
            String value = loadConvert(lr.lineBuf, valueStart, limit - valueStart, outBuffer);
            put(key, value);
        }
    }

    /* Read in a "logical line" from an InputStream/Reader, skip all comment
     * and blank lines and filter out those leading whitespace characters
     * (\u0020, \u0009 and \u000c) from the beginning of a "natural line".
     * Method returns the char length of the "logical line" and stores
     * the line in "lineBuf".
     */
    private static class LineReader {
        LineReader(InputStream inStream) {
            this.inStream = inStream;
            inByteBuf = new byte[8192];
        }

        LineReader(Reader reader) {
            this.reader = reader;
            inCharBuf = new char[8192];
        }

        char[] lineBuf = new char[1024];
        private byte[] inByteBuf;
        private char[] inCharBuf;
        private int inLimit = 0;
        private int inOff = 0;
        private InputStream inStream;
        private Reader reader;

        int readLine() throws IOException {
            // use locals to optimize for interpreted performance
            int len = 0;
            int off = inOff;
            int limit = inLimit;

            boolean skipWhiteSpace = true;
            boolean appendedLineBegin = false;
            boolean precedingBackslash = false;
            boolean fromStream = inStream != null;
            byte[] byteBuf = inByteBuf;
            char[] charBuf = inCharBuf;
            char[] lineBuf = this.lineBuf;
            char c;

            while (true) {
                if (off >= limit) {
                    inLimit = limit = fromStream ? inStream.read(byteBuf)
                                                 : reader.read(charBuf);
                    if (limit <= 0) {
                        if (len == 0) {
                            return -1;
                        }
                        return precedingBackslash ? len - 1 : len;
                    }
                    off = 0;
                }

                // (char)(byte & 0xFF) is equivalent to calling a ISO8859-1 decoder.
                c = (fromStream) ? (char)(byteBuf[off++] & 0xFF) : charBuf[off++];

                if (skipWhiteSpace) {
                    if (c == ' ' || c == '\t' || c == '\f') {
                        continue;
                    }
                    if (!appendedLineBegin && (c == '\r' || c == '\n')) {
                        continue;
                    }
                    skipWhiteSpace = false;
                    appendedLineBegin = false;

                }
                if (len == 0) { // Still on a new logical line
                    if (c == '#' || c == '!') {
                        // Comment, quickly consume the rest of the line

                        // When checking for new line characters a range check,
                        // starting with the higher bound ('\r') means one less
                        // branch in the common case.
                        commentLoop: while (true) {
                            if (fromStream) {
                                byte b;
                                while (off < limit) {
                                    b = byteBuf[off++];
                                    if (b <= '\r' && (b == '\r' || b == '\n'))
                                        break commentLoop;
                                }
                                if (off == limit) {
                                    inLimit = limit = inStream.read(byteBuf);
                                    if (limit <= 0) { // EOF
                                        return -1;
                                    }
                                    off = 0;
                                }
                            } else {
                                while (off < limit) {
                                    c = charBuf[off++];
                                    if (c <= '\r' && (c == '\r' || c == '\n'))
                                        break commentLoop;
                                }
                                if (off == limit) {
                                    inLimit = limit = reader.read(charBuf);
                                    if (limit <= 0) { // EOF
                                        return -1;
                                    }
                                    off = 0;
                                }
                            }
                        }
                        skipWhiteSpace = true;
                        continue;
                    }
                }

                if (c != '\n' && c != '\r') {
                    lineBuf[len++] = c;
                    if (len == lineBuf.length) {
                        int maxLen = Integer.MAX_VALUE - 8; // VM allocation limit
                        int newLen = len * 2;
                        if (newLen < 0 || newLen > maxLen) { // check for under/overflow
                            newLen = maxLen;
                        }
                        if (newLen <= len) { // still not good? last-ditch attempt then
                           if (len != Integer.MAX_VALUE) {
                               newLen = len + 1;
                           } else {
                               throw new OutOfMemoryError("Required array length too large");
                           }
                        }
                        lineBuf = new char[newLen];
                        System.arraycopy(this.lineBuf, 0, lineBuf, 0, len);
                        this.lineBuf = lineBuf;
                    }
                    // flip the preceding backslash flag
                    precedingBackslash = (c == '\\') ? !precedingBackslash : false;
                } else {
                    // reached EOL
                    if (len == 0) {
                        skipWhiteSpace = true;
                        continue;
                    }
                    if (off >= limit) {
                        inLimit = limit = fromStream ? inStream.read(byteBuf)
                                                     : reader.read(charBuf);
                        off = 0;
                        if (limit <= 0) { // EOF
                            return precedingBackslash ? len - 1 : len;
                        }
                    }
                    if (precedingBackslash) {
                        // backslash at EOL is not part of the line
                        len -= 1;
                        // skip leading whitespace characters in the following line
                        skipWhiteSpace = true;
                        appendedLineBegin = true;
                        precedingBackslash = false;
                        // take care not to include any subsequent \n
                        if (c == '\r') {
                            if (fromStream) {
                                if (byteBuf[off] == '\n') {
                                    off++;
                                }
                            } else {
                                if (charBuf[off] == '\n') {
                                    off++;
                                }
                            }
                        }
                    } else {
                        inOff = off;
                        return len;
                    }
                }
            }
        }
    }

    /*
     * Converts encoded &#92;uxxxx to unicode chars
     * and changes special saved chars to their original forms
     */
    private String loadConvert(char[] in, int off, int len, StringBuilder out) {
        char aChar;
        int end = off + len;
        int start = off;
        while (off < end) {
            aChar = in[off++];
            if (aChar == '\\') {
                break;
            }
        }
        if (off == end) { // No backslash
            return new String(in, start, len);
        }

        // backslash found at off - 1, reset the shared buffer, rewind offset
        out.setLength(0);
        off--;
        out.append(in, start, off - start);

        while (off < end) {
            aChar = in[off++];
            if (aChar == '\\') {
                aChar = in[off++];
                if(aChar == 'u') {
                    // Read the xxxx
                    int value=0;
                    for (int i=0; i<4; i++) {
                        aChar = in[off++];
                        switch (aChar) {
                          case '0': case '1': case '2': case '3': case '4':
                          case '5': case '6': case '7': case '8': case '9':
                             value = (value << 4) + aChar - '0';
                             break;
                          case 'a': case 'b': case 'c':
                          case 'd': case 'e': case 'f':
                             value = (value << 4) + 10 + aChar - 'a';
                             break;
                          case 'A': case 'B': case 'C':
                          case 'D': case 'E': case 'F':
                             value = (value << 4) + 10 + aChar - 'A';
                             break;
                          default:
                              throw new IllegalArgumentException(
                                           "Malformed \\uxxxx encoding.");
                        }
                    }
                    out.append((char)value);
                } else {
                    if (aChar == 't') aChar = '\t';
                    else if (aChar == 'r') aChar = '\r';
                    else if (aChar == 'n') aChar = '\n';
                    else if (aChar == 'f') aChar = '\f';
                    out.append(aChar);
                }
            } else {
                out.append(aChar);
            }
        }
        return out.toString();
    }

    /*
     * Converts unicodes to encoded &#92;uxxxx and escapes
     * special characters with a preceding slash
     */
    private String saveConvert(String theString,
                               boolean escapeSpace,
                               boolean escapeUnicode) {
        int len = theString.length();
        int bufLen = len * 2;
        if (bufLen < 0) {
            bufLen = Integer.MAX_VALUE;
        }
        StringBuilder outBuffer = new StringBuilder(bufLen);

        for(int x=0; x<len; x++) {
            char aChar = theString.charAt(x);
            // Handle common case first, selecting largest block that
            // avoids the specials below
            if ((aChar > 61) && (aChar < 127)) {
                if (aChar == '\\') {
                    outBuffer.append('\\'); outBuffer.append('\\');
                    continue;
                }
                outBuffer.append(aChar);
                continue;
            }
            switch(aChar) {
                case ' ':
                    if (x == 0 || escapeSpace)
                        outBuffer.append('\\');
                    outBuffer.append(' ');
                    break;
                case '\t':outBuffer.append('\\'); outBuffer.append('t');
                          break;
                case '\n':outBuffer.append('\\'); outBuffer.append('n');
                          break;
                case '\r':outBuffer.append('\\'); outBuffer.append('r');
                          break;
                case '\f':outBuffer.append('\\'); outBuffer.append('f');
                          break;
                case '=': // Fall through
                case ':': // Fall through
                case '#': // Fall through
                case '!':
                    outBuffer.append('\\'); outBuffer.append(aChar);
                    break;
                default:
                    if (((aChar < 0x0020) || (aChar > 0x007e)) & escapeUnicode ) {
                        outBuffer.append('\\');
                        outBuffer.append('u');
                        outBuffer.append(toHex((aChar >> 12) & 0xF));
                        outBuffer.append(toHex((aChar >>  8) & 0xF));
                        outBuffer.append(toHex((aChar >>  4) & 0xF));
                        outBuffer.append(toHex( aChar        & 0xF));
                    } else {
                        outBuffer.append(aChar);
                    }
            }
        }
        return outBuffer.toString();
    }

    private static void writeComments(BufferedWriter bw, String comments)
        throws IOException {
        bw.write("#");
        int len = comments.length();
        int current = 0;
        int last = 0;
        char[] uu = new char[6];
        uu[0] = '\\';
        uu[1] = 'u';
        while (current < len) {
            char c = comments.charAt(current);
            if (c > '\u00ff' || c == '\n' || c == '\r') {
                if (last != current)
                    bw.write(comments.substring(last, current));
                if (c > '\u00ff') {
                    uu[2] = toHex((c >> 12) & 0xf);
                    uu[3] = toHex((c >>  8) & 0xf);
                    uu[4] = toHex((c >>  4) & 0xf);
                    uu[5] = toHex( c        & 0xf);
                    bw.write(new String(uu));
                } else {
                    bw.newLine();
                    if (c == '\r' &&
                        current != len - 1 &&
                        comments.charAt(current + 1) == '\n') {
                        current++;
                    }
                    if (current == len - 1 ||
                        (comments.charAt(current + 1) != '#' &&
                        comments.charAt(current + 1) != '!'))
                        bw.write("#");
                }
                last = current + 1;
            }
            current++;
        }
        if (last != current)
            bw.write(comments.substring(last, current));
        bw.newLine();
    }

    /**
     * Calls the {@code store(OutputStream out, String comments)} method
     * and suppresses IOExceptions that were thrown.
     *
     * @deprecated This method does not throw an IOException if an I/O error
     * occurs while saving the property list.  The preferred way to save a
     * properties list is via the {@code store(OutputStream out,
     * String comments)} method or the
     * {@code storeToXML(OutputStream os, String comment)} method.
     *
     * @param   out      an output stream.
     * @param   comments   a description of the property list.
     * @exception  ClassCastException  if this {@code Properties} object
     *             contains any keys or values that are not
     *             {@code Strings}.
     */
    @Deprecated
    public void save(OutputStream out, String comments)  {
        try {
            store(out, comments);
        } catch (IOException e) {
        }
    }

    /**
     * Writes this property list (key and element pairs) in this
     * {@code Properties} table to the output character stream in a
     * format suitable for using the {@link #load(java.io.Reader) load(Reader)}
     * method.
     * <p>
     * Properties from the defaults table of this {@code Properties}
     * table (if any) are <i>not</i> written out by this method.
     * <p>
     * If the comments argument is not null, then an ASCII {@code #}
     * character, the comments string, and a line separator are first written
     * to the output stream. Thus, the {@code comments} can serve as an
     * identifying comment. Any one of a line feed ('\n'), a carriage
     * return ('\r'), or a carriage return followed immediately by a line feed
     * in comments is replaced by a line separator generated by the {@code Writer}
     * and if the next character in comments is not character {@code #} or
     * character {@code !} then an ASCII {@code #} is written out
     * after that line separator.
     * <p>
     * Next, a comment line is always written, consisting of an ASCII
     * {@code #} character, the current date and time (as if produced
     * by the {@code toString} method of {@code Date} for the
     * current time), and a line separator as generated by the {@code Writer}.
     * <p>
     * Then every entry in this {@code Properties} table is
     * written out, one per line. For each entry the key string is
     * written, then an ASCII {@code =}, then the associated
     * element string. For the key, all space characters are
     * written with a preceding {@code \} character.  For the
     * element, leading space characters, but not embedded or trailing
     * space characters, are written with a preceding {@code \}
     * character. The key and element characters {@code #},
     * {@code !}, {@code =}, and {@code :} are written
     * with a preceding backslash to ensure that they are properly loaded.
     * <p>
     * After the entries have been written, the output stream is flushed.
     * The output stream remains open after this method returns.
     *
     * @param   writer      an output character stream writer.
     * @param   comments   a description of the property list.
     * @exception  IOException if writing this property list to the specified
     *             output stream throws an {@code IOException}.
     * @exception  ClassCastException  if this {@code Properties} object
     *             contains any keys or values that are not {@code Strings}.
     * @exception  NullPointerException  if {@code writer} is null.
     * @since 1.6
     */
    public void store(Writer writer, String comments)
        throws IOException
    {
        store0((writer instanceof BufferedWriter)?(BufferedWriter)writer
                                                 : new BufferedWriter(writer),
               comments,
               false);
    }

    /**
     * Writes this property list (key and element pairs) in this
     * {@code Properties} table to the output stream in a format suitable
     * for loading into a {@code Properties} table using the
     * {@link #load(InputStream) load(InputStream)} method.
     * <p>
     * Properties from the defaults table of this {@code Properties}
     * table (if any) are <i>not</i> written out by this method.
     * <p>
     * This method outputs the comments, properties keys and values in
     * the same format as specified in
     * {@link #store(java.io.Writer, java.lang.String) store(Writer)},
     * with the following differences:
     * <ul>
     * <li>The stream is written using the ISO 8859-1 character encoding.
     *
     * <li>Characters not in Latin-1 in the comments are written as
     * {@code \u005Cu}<i>xxxx</i> for their appropriate unicode
     * hexadecimal value <i>xxxx</i>.
     *
     * <li>Characters less than {@code \u005Cu0020} and characters greater
     * than {@code \u005Cu007E} in property keys or values are written
     * as {@code \u005Cu}<i>xxxx</i> for the appropriate hexadecimal
     * value <i>xxxx</i>.
     * </ul>
     * <p>
     * After the entries have been written, the output stream is flushed.
     * The output stream remains open after this method returns.
     *
     * @param   out      an output stream.
     * @param   comments   a description of the property list.
     * @exception  IOException if writing this property list to the specified
     *             output stream throws an {@code IOException}.
     * @exception  ClassCastException  if this {@code Properties} object
     *             contains any keys or values that are not {@code Strings}.
     * @exception  NullPointerException  if {@code out} is null.
     * @since 1.2
     */
    public void store(OutputStream out, String comments)
        throws IOException
    {
        store0(new BufferedWriter(new OutputStreamWriter(out, ISO_8859_1.INSTANCE)),
               comments,
               true);
    }

    private void store0(BufferedWriter bw, String comments, boolean escUnicode)
        throws IOException
    {
        if (comments != null) {
            writeComments(bw, comments);
        }
        bw.write("#" + new Date().toString());
        bw.newLine();
        synchronized (this) {
            for (Map.Entry<Object, Object> e : entrySet()) {
                String key = (String)e.getKey();
                String val = (String)e.getValue();
                key = saveConvert(key, true, escUnicode);
                /* No need to escape embedded and trailing spaces for value, hence
                 * pass false to flag.
                 */
                val = saveConvert(val, false, escUnicode);
                bw.write(key + "=" + val);
                bw.newLine();
            }
        }
        bw.flush();
    }

    /**
     * Loads all of the properties represented by the XML document on the
     * specified input stream into this properties table.
     *
     * <p>The XML document must have the following DOCTYPE declaration:
     * <pre>
     * &lt;!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd"&gt;
     * </pre>
     * Furthermore, the document must satisfy the properties DTD described
     * above.
     *
     * <p> An implementation is required to read XML documents that use the
     * "{@code UTF-8}" or "{@code UTF-16}" encoding. An implementation may
     * support additional encodings.
     *
     * <p>The specified stream is closed after this method returns.
     *
     * @param in the input stream from which to read the XML document.
     * @throws IOException if reading from the specified input stream
     *         results in an {@code IOException}.
     * @throws java.io.UnsupportedEncodingException if the document's encoding
     *         declaration can be read and it specifies an encoding that is not
     *         supported
     * @throws InvalidPropertiesFormatException Data on input stream does not
     *         constitute a valid XML document with the mandated document type.
     * @throws NullPointerException if {@code in} is null.
     * @see    #storeToXML(OutputStream, String, String)
     * @see    <a href="http://www.w3.org/TR/REC-xml/#charencoding">Character
     *         Encoding in Entities</a>
     * @since 1.5
     */
    public synchronized void loadFromXML(InputStream in)
        throws IOException, InvalidPropertiesFormatException
    {
        Objects.requireNonNull(in);
        PropertiesDefaultHandler handler = new PropertiesDefaultHandler();
        handler.load(this, in);
        in.close();
    }

    /**
     * Emits an XML document representing all of the properties contained
     * in this table.
     *
     * <p> An invocation of this method of the form {@code props.storeToXML(os,
     * comment)} behaves in exactly the same way as the invocation
     * {@code props.storeToXML(os, comment, "UTF-8");}.
     *
     * @param os the output stream on which to emit the XML document.
     * @param comment a description of the property list, or {@code null}
     *        if no comment is desired.
     * @throws IOException if writing to the specified output stream
     *         results in an {@code IOException}.
     * @throws NullPointerException if {@code os} is null.
     * @throws ClassCastException  if this {@code Properties} object
     *         contains any keys or values that are not
     *         {@code Strings}.
     * @see    #loadFromXML(InputStream)
     * @since 1.5
     */
    public void storeToXML(OutputStream os, String comment)
        throws IOException
    {
        storeToXML(os, comment, UTF_8.INSTANCE);
    }

    /**
     * Emits an XML document representing all of the properties contained
     * in this table, using the specified encoding.
     *
     * <p>The XML document will have the following DOCTYPE declaration:
     * <pre>
     * &lt;!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd"&gt;
     * </pre>
     *
     * <p>If the specified comment is {@code null} then no comment
     * will be stored in the document.
     *
     * <p> An implementation is required to support writing of XML documents
     * that use the "{@code UTF-8}" or "{@code UTF-16}" encoding. An
     * implementation may support additional encodings.
     *
     * <p>The specified stream remains open after this method returns.
     *
     * <p>This method behaves the same as
     * {@linkplain #storeToXML(OutputStream os, String comment, Charset charset)}
     * except that it will {@linkplain java.nio.charset.Charset#forName look up the charset}
     * using the given encoding name.
     *
     * @param os        the output stream on which to emit the XML document.
     * @param comment   a description of the property list, or {@code null}
     *                  if no comment is desired.
     * @param  encoding the name of a supported
     *                  <a href="../lang/package-summary.html#charenc">
     *                  character encoding</a>
     *
     * @throws IOException if writing to the specified output stream
     *         results in an {@code IOException}.
     * @throws java.io.UnsupportedEncodingException if the encoding is not
     *         supported by the implementation.
     * @throws NullPointerException if {@code os} is {@code null},
     *         or if {@code encoding} is {@code null}.
     * @throws ClassCastException  if this {@code Properties} object
     *         contains any keys or values that are not {@code Strings}.
     * @see    #loadFromXML(InputStream)
     * @see    <a href="http://www.w3.org/TR/REC-xml/#charencoding">Character
     *         Encoding in Entities</a>
     * @since 1.5
     */
    public void storeToXML(OutputStream os, String comment, String encoding)
        throws IOException {
        Objects.requireNonNull(os);
        Objects.requireNonNull(encoding);

        try {
            Charset charset = Charset.forName(encoding);
            storeToXML(os, comment, charset);
        } catch (IllegalCharsetNameException | UnsupportedCharsetException e) {
            throw new UnsupportedEncodingException(encoding);
        }
    }

    /**
     * Emits an XML document representing all of the properties contained
     * in this table, using the specified encoding.
     *
     * <p>The XML document will have the following DOCTYPE declaration:
     * <pre>
     * &lt;!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd"&gt;
     * </pre>
     *
     * <p>If the specified comment is {@code null} then no comment
     * will be stored in the document.
     *
     * <p> An implementation is required to support writing of XML documents
     * that use the "{@code UTF-8}" or "{@code UTF-16}" encoding. An
     * implementation may support additional encodings.
     *
     * <p> Unmappable characters for the specified charset will be encoded as
     * numeric character references.
     *
     * <p>The specified stream remains open after this method returns.
     *
     * @param os        the output stream on which to emit the XML document.
     * @param comment   a description of the property list, or {@code null}
     *                  if no comment is desired.
     * @param charset   the charset
     *
     * @throws IOException if writing to the specified output stream
     *         results in an {@code IOException}.
     * @throws NullPointerException if {@code os} or {@code charset} is {@code null}.
     * @throws ClassCastException  if this {@code Properties} object
     *         contains any keys or values that are not {@code Strings}.
     * @see    #loadFromXML(InputStream)
     * @see    <a href="http://www.w3.org/TR/REC-xml/#charencoding">Character
     *         Encoding in Entities</a>
     * @since 10
     */
    public void storeToXML(OutputStream os, String comment, Charset charset)
        throws IOException {
        Objects.requireNonNull(os, "OutputStream");
        Objects.requireNonNull(charset, "Charset");
        PropertiesDefaultHandler handler = new PropertiesDefaultHandler();
        handler.store(this, os, comment, charset);
    }

    /**
     * Searches for the property with the specified key in this property list.
     * If the key is not found in this property list, the default property list,
     * and its defaults, recursively, are then checked. The method returns
     * {@code null} if the property is not found.
     *
     * @param   key   the property key.
     * @return  the value in this property list with the specified key value.
     * @see     #setProperty
     * @see     #defaults
     */
    public String getProperty(String key) {
        Object oval = map.get(key);
        String sval = (oval instanceof String) ? (String)oval : null;
        Properties defaults;
        return ((sval == null) && ((defaults = this.defaults) != null)) ? defaults.getProperty(key) : sval;
    }

    /**
     * Searches for the property with the specified key in this property list.
     * If the key is not found in this property list, the default property list,
     * and its defaults, recursively, are then checked. The method returns the
     * default value argument if the property is not found.
     *
     * @param   key            the hashtable key.
     * @param   defaultValue   a default value.
     *
     * @return  the value in this property list with the specified key value.
     * @see     #setProperty
     * @see     #defaults
     */
    public String getProperty(String key, String defaultValue) {
        String val = getProperty(key);
        return (val == null) ? defaultValue : val;
    }

    /**
     * Returns an enumeration of all the keys in this property list,
     * including distinct keys in the default property list if a key
     * of the same name has not already been found from the main
     * properties list.
     *
     * @return  an enumeration of all the keys in this property list, including
     *          the keys in the default property list.
     * @throws  ClassCastException if any key in this property list
     *          is not a string.
     * @see     java.util.Enumeration
     * @see     java.util.Properties#defaults
     * @see     #stringPropertyNames
     */
    public Enumeration<?> propertyNames() {
        Hashtable<String,Object> h = new Hashtable<>();
        enumerate(h);
        return h.keys();
    }

    /**
     * Returns an unmodifiable set of keys from this property list
     * where the key and its corresponding value are strings,
     * including distinct keys in the default property list if a key
     * of the same name has not already been found from the main
     * properties list.  Properties whose key or value is not
     * of type {@code String} are omitted.
     * <p>
     * The returned set is not backed by this {@code Properties} object.
     * Changes to this {@code Properties} object are not reflected in the
     * returned set.
     *
     * @return  an unmodifiable set of keys in this property list where
     *          the key and its corresponding value are strings,
     *          including the keys in the default property list.
     * @see     java.util.Properties#defaults
     * @since   1.6
     */
    public Set<String> stringPropertyNames() {
        Map<String, String> h = new HashMap<>();
        enumerateStringProperties(h);
        return Collections.unmodifiableSet(h.keySet());
    }

    /**
     * Prints this property list out to the specified output stream.
     * This method is useful for debugging.
     *
     * @param   out   an output stream.
     * @throws  ClassCastException if any key in this property list
     *          is not a string.
     */
    public void list(PrintStream out) {
        out.println("-- listing properties --");
        Map<String, Object> h = new HashMap<>();
        enumerate(h);
        for (Map.Entry<String, Object> e : h.entrySet()) {
            String key = e.getKey();
            String val = (String)e.getValue();
            if (val.length() > 40) {
                val = val.substring(0, 37) + "...";
            }
            out.println(key + "=" + val);
        }
    }

    /**
     * Prints this property list out to the specified output stream.
     * This method is useful for debugging.
     *
     * @param   out   an output stream.
     * @throws  ClassCastException if any key in this property list
     *          is not a string.
     * @since   1.1
     */
    /*
     * Rather than use an anonymous inner class to share common code, this
     * method is duplicated in order to ensure that a non-1.1 compiler can
     * compile this file.
     */
    public void list(PrintWriter out) {
        out.println("-- listing properties --");
        Map<String, Object> h = new HashMap<>();
        enumerate(h);
        for (Map.Entry<String, Object> e : h.entrySet()) {
            String key = e.getKey();
            String val = (String)e.getValue();
            if (val.length() > 40) {
                val = val.substring(0, 37) + "...";
            }
            out.println(key + "=" + val);
        }
    }

    /**
     * Enumerates all key/value pairs into the specified Map.
     * @param h the Map
     * @throws ClassCastException if any of the property keys
     *         is not of String type.
     */
    private void enumerate(Map<String, Object> h) {
        if (defaults != null) {
            defaults.enumerate(h);
        }
        for (Map.Entry<Object, Object> e : entrySet()) {
            String key = (String)e.getKey();
            h.put(key, e.getValue());
        }
    }

    /**
     * Enumerates all key/value pairs into the specified Map
     * and omits the property if the key or value is not a string.
     * @param h the Map
     */
    private void enumerateStringProperties(Map<String, String> h) {
        if (defaults != null) {
            defaults.enumerateStringProperties(h);
        }
        for (Map.Entry<Object, Object> e : entrySet()) {
            Object k = e.getKey();
            Object v = e.getValue();
            if (k instanceof String && v instanceof String) {
                h.put((String) k, (String) v);
            }
        }
    }

    /**
     * Convert a nibble to a hex character
     * @param   nibble  the nibble to convert.
     */
    private static char toHex(int nibble) {
        return hexDigit[(nibble & 0xF)];
    }

    /** A table of hex digits */
    private static final char[] hexDigit = {
        '0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'
    };

    //
    // Hashtable methods overridden and delegated to a ConcurrentHashMap instance

    @Override
    public int size() {
        return map.size();
    }

    @Override
    public boolean isEmpty() {
        return map.isEmpty();
    }

    @Override
    public Enumeration<Object> keys() {
        // CHM.keys() returns Iterator w/ remove() - instead wrap keySet()
        return Collections.enumeration(map.keySet());
    }

    @Override
    public Enumeration<Object> elements() {
        // CHM.elements() returns Iterator w/ remove() - instead wrap values()
        return Collections.enumeration(map.values());
    }

    @Override
    public boolean contains(Object value) {
        return map.contains(value);
    }

    @Override
    public boolean containsValue(Object value) {
        return map.containsValue(value);
    }

    @Override
    public boolean containsKey(Object key) {
        return map.containsKey(key);
    }

    @Override
    public Object get(Object key) {
        return map.get(key);
    }

    @Override
    public synchronized Object put(Object key, Object value) {
        return map.put(key, value);
    }

    @Override
    public synchronized Object remove(Object key) {
        return map.remove(key);
    }

    @Override
    public synchronized void putAll(Map<?, ?> t) {
        map.putAll(t);
    }

    @Override
    public synchronized void clear() {
        map.clear();
    }

    @Override
    public synchronized String toString() {
        return map.toString();
    }

    @Override
    public Set<Object> keySet() {
        return Collections.synchronizedSet(map.keySet(), this);
    }

    @Override
    public Collection<Object> values() {
        return Collections.synchronizedCollection(map.values(), this);
    }

    @Override
    public Set<Map.Entry<Object, Object>> entrySet() {
        return Collections.synchronizedSet(new EntrySet(map.entrySet()), this);
    }

    /*
     * Properties.entrySet() should not support add/addAll, however
     * ConcurrentHashMap.entrySet() provides add/addAll.  This class wraps the
     * Set returned from CHM, changing add/addAll to throw UOE.
     */
    private static class EntrySet implements Set<Map.Entry<Object, Object>> {
        private Set<Map.Entry<Object,Object>> entrySet;

        private EntrySet(Set<Map.Entry<Object, Object>> entrySet) {
            this.entrySet = entrySet;
        }

        @Override public int size() { return entrySet.size(); }
        @Override public boolean isEmpty() { return entrySet.isEmpty(); }
        @Override public boolean contains(Object o) { return entrySet.contains(o); }
        @Override public Object[] toArray() { return entrySet.toArray(); }
        @Override public <T> T[] toArray(T[] a) { return entrySet.toArray(a); }
        @Override public void clear() { entrySet.clear(); }
        @Override public boolean remove(Object o) { return entrySet.remove(o); }

        @Override
        public boolean add(Map.Entry<Object, Object> e) {
            throw new UnsupportedOperationException();
        }

        @Override
        public boolean addAll(Collection<? extends Map.Entry<Object, Object>> c) {
            throw new UnsupportedOperationException();
        }

        @Override
        public boolean containsAll(Collection<?> c) {
            return entrySet.containsAll(c);
        }

        @Override
        public boolean removeAll(Collection<?> c) {
            return entrySet.removeAll(c);
        }

        @Override
        public boolean retainAll(Collection<?> c) {
            return entrySet.retainAll(c);
        }

        @Override
        public Iterator<Map.Entry<Object, Object>> iterator() {
            return entrySet.iterator();
        }
    }

    @Override
    public synchronized boolean equals(Object o) {
        return map.equals(o);
    }

    @Override
    public synchronized int hashCode() {
        return map.hashCode();
    }

    @Override
    public Object getOrDefault(Object key, Object defaultValue) {
        return map.getOrDefault(key, defaultValue);
    }

    @Override
    public synchronized void forEach(BiConsumer<? super Object, ? super Object> action) {
        map.forEach(action);
    }

    @Override
    public synchronized void replaceAll(BiFunction<? super Object, ? super Object, ?> function) {
        map.replaceAll(function);
    }

    @Override
    public synchronized Object putIfAbsent(Object key, Object value) {
        return map.putIfAbsent(key, value);
    }

    @Override
    public synchronized boolean remove(Object key, Object value) {
        return map.remove(key, value);
    }

    @Override
    public synchronized boolean replace(Object key, Object oldValue, Object newValue) {
        return map.replace(key, oldValue, newValue);
    }

    @Override
    public synchronized Object replace(Object key, Object value) {
        return map.replace(key, value);
    }

    @Override
    public synchronized Object computeIfAbsent(Object key,
            Function<? super Object, ?> mappingFunction) {
        return map.computeIfAbsent(key, mappingFunction);
    }

    @Override
    public synchronized Object computeIfPresent(Object key,
            BiFunction<? super Object, ? super Object, ?> remappingFunction) {
        return map.computeIfPresent(key, remappingFunction);
    }

    @Override
    public synchronized Object compute(Object key,
            BiFunction<? super Object, ? super Object, ?> remappingFunction) {
        return map.compute(key, remappingFunction);
    }

    @Override
    public synchronized Object merge(Object key, Object value,
            BiFunction<? super Object, ? super Object, ?> remappingFunction) {
        return map.merge(key, value, remappingFunction);
    }

    //
    // Special Hashtable methods

    @Override
    protected void rehash() { /* no-op */ }

    @Override
    public synchronized Object clone() {
        Properties clone = (Properties) cloneHashtable();
        clone.map = new ConcurrentHashMap<>(map);
        return clone;
    }

    //
    // Hashtable serialization overrides
    // (these should emit and consume Hashtable-compatible stream)

    @Override
    void writeHashtable(ObjectOutputStream s) throws IOException {
        var map = this.map;
        List<Object> entryStack = new ArrayList<>(map.size() * 2); // an estimate

        for (Map.Entry<Object, Object> entry : map.entrySet()) {
            entryStack.add(entry.getValue());
            entryStack.add(entry.getKey());
        }

        // Write out the simulated threshold, loadfactor
        float loadFactor = 0.75f;
        int count = entryStack.size() / 2;
        int length = (int)(count / loadFactor) + (count / 20) + 3;
        if (length > count && (length & 1) == 0) {
            length--;
        }
        synchronized (map) { // in case of multiple concurrent serializations
            defaultWriteHashtable(s, length, loadFactor);
        }

        // Write out simulated length and real count of elements
        s.writeInt(length);
        s.writeInt(count);

        // Write out the key/value objects from the stacked entries
        for (int i = entryStack.size() - 1; i >= 0; i--) {
            s.writeObject(entryStack.get(i));
        }
    }

    @Override
    void readHashtable(ObjectInputStream s) throws IOException,
            ClassNotFoundException {
        // Read in the threshold and loadfactor
        s.defaultReadObject();

        // Read the original length of the array and number of elements
        int origlength = s.readInt();
        int elements = s.readInt();

        // Validate # of elements
        if (elements < 0) {
            throw new StreamCorruptedException("Illegal # of Elements: " + elements);
        }

        // Constructing the backing map will lazily create an array when the first element is
        // added, so check it before construction. Note that CHM's constructor takes a size
        // that is the number of elements to be stored -- not the table size -- so it must be
        // inflated by the default load factor of 0.75, then inflated to the next power of two.
        // (CHM uses the same power-of-two computation as HashMap, and HashMap.tableSizeFor is
        // accessible here.) Check Map.Entry[].class since it's the nearest public type to
        // what is actually created.
        SharedSecrets.getJavaObjectInputStreamAccess()
                     .checkArray(s, Map.Entry[].class, HashMap.tableSizeFor((int)(elements / 0.75)));

        // create CHM of appropriate capacity
        var map = new ConcurrentHashMap<>(elements);

        // Read all the key/value objects
        for (; elements > 0; elements--) {
            Object key = s.readObject();
            Object value = s.readObject();
            map.put(key, value);
        }
        this.map = map;
    }
}