1 /*
2  * Copyright (C) 2011 The Guava Authors
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package org.whispersystems.libsignal.util.guava;
18 
19 import static org.whispersystems.libsignal.util.guava.Preconditions.checkNotNull;
20 
21 
22 
23 import java.util.Collections;
24 import java.util.Set;
25 
26 
27 /**
28  * Implementation of an {@link Optional} not containing a reference.
29  */
30 
31 final class Absent extends Optional<Object> {
32   static final Absent INSTANCE = new Absent();
33 
isPresent()34   @Override public boolean isPresent() {
35     return false;
36   }
37 
get()38   @Override public Object get() {
39     throw new IllegalStateException("value is absent");
40   }
41 
or(Object defaultValue)42   @Override public Object or(Object defaultValue) {
43     return checkNotNull(defaultValue, "use orNull() instead of or(null)");
44   }
45 
46   @SuppressWarnings("unchecked") // safe covariant cast
or(Optional<?> secondChoice)47   @Override public Optional<Object> or(Optional<?> secondChoice) {
48     return (Optional) checkNotNull(secondChoice);
49   }
50 
or(Supplier<?> supplier)51   @Override public Object or(Supplier<?> supplier) {
52     return checkNotNull(supplier.get(),
53         "use orNull() instead of a Supplier that returns null");
54   }
55 
orNull()56   @Override public Object orNull() {
57     return null;
58   }
59 
asSet()60   @Override public Set<Object> asSet() {
61     return Collections.emptySet();
62   }
63 
64   @Override
transform(Function<? super Object, V> function)65   public <V> Optional<V> transform(Function<? super Object, V> function) {
66     checkNotNull(function);
67     return Optional.absent();
68   }
69 
equals(Object object)70   @Override public boolean equals(Object object) {
71     return object == this;
72   }
73 
hashCode()74   @Override public int hashCode() {
75     return 0x598df91c;
76   }
77 
toString()78   @Override public String toString() {
79     return "Optional.absent()";
80   }
81 
readResolve()82   private Object readResolve() {
83     return INSTANCE;
84   }
85 
86   private static final long serialVersionUID = 0;
87 }
88