awt/event/HierarchyEvent.java

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package java.awt.event;

import java.awt.AWTEvent;
import java.awt.Component;
import java.awt.Container;

/**
 * An event which indicates a change to the {@code Component}
 * hierarchy to which {@code Component} belongs.
 * <ul>
 * <li>Hierarchy Change Events (HierarchyListener)
 *     <ul>
 *     <li> addition of an ancestor
 *     <li> removal of an ancestor
 *     <li> hierarchy made displayable
 *     <li> hierarchy made undisplayable
 *     <li> hierarchy shown on the screen (both visible and displayable)
 *     <li> hierarchy hidden on the screen (either invisible or undisplayable)
 *     </ul>
 * <li>Ancestor Reshape Events (HierarchyBoundsListener)
 *     <ul>
 *     <li> an ancestor was resized
 *     <li> an ancestor was moved
 *     </ul>
 * </ul>
 * <p>
 * Hierarchy events are provided for notification purposes ONLY.
 * The AWT will automatically handle changes to the hierarchy internally so
 * that GUI layout and displayability works properly regardless of whether a
 * program is receiving these events or not.
 * <p>
 * This event is generated by a Container object (such as a Panel) when the
 * Container is added, removed, moved, or resized, and passed down the
 * hierarchy. It is also generated by a Component object when that object's
 * {@code addNotify}, {@code removeNotify}, {@code show}, or
 * {@code hide} method is called. The {@code ANCESTOR_MOVED} and
 * {@code ANCESTOR_RESIZED}
 * events are dispatched to every {@code HierarchyBoundsListener} or
 * {@code HierarchyBoundsAdapter} object which registered to receive
 * such events using the Component's {@code addHierarchyBoundsListener}
 * method. ({@code HierarchyBoundsAdapter} objects implement the
 * {@code HierarchyBoundsListener} interface.) The {@code HIERARCHY_CHANGED} events are
 * dispatched to every {@code HierarchyListener} object which registered
 * to receive such events using the Component's {@code addHierarchyListener}
 * method. Each such listener object gets this {@code HierarchyEvent}
 * when the event occurs.
 * <p>
 * An unspecified behavior will be caused if the {@code id} parameter
 * of any particular {@code HierarchyEvent} instance is not
 * in the range from {@code HIERARCHY_FIRST} to {@code HIERARCHY_LAST}.
 * <br>
 * The {@code changeFlags} parameter of any {@code HierarchyEvent} instance takes one of the following
 * values:
 * <ul>
 * <li> {@code HierarchyEvent.PARENT_CHANGED}
 * <li> {@code HierarchyEvent.DISPLAYABILITY_CHANGED}
 * <li> {@code HierarchyEvent.SHOWING_CHANGED}
 * </ul>
 * Assigning the value different from listed above will cause unspecified behavior.
 *
 * @author      David Mendenhall
 * @see         HierarchyListener
 * @see         HierarchyBoundsAdapter
 * @see         HierarchyBoundsListener
 * @since       1.3
 */
public class HierarchyEvent extends AWTEvent {
    /*
     * serialVersionUID
     */
    private static final long serialVersionUID = -5337576970038043990L;

    /**
     * Marks the first integer id for the range of hierarchy event ids.
     */
    public static final int HIERARCHY_FIRST = 1400; // 1300 used by sun.awt.windows.ModalityEvent

    /**
     * The event id indicating that modification was made to the
     * entire hierarchy tree.
     */
    public static final int HIERARCHY_CHANGED = HIERARCHY_FIRST;

    /**
     * The event id indicating an ancestor-Container was moved.
     */
    public static final int ANCESTOR_MOVED = 1 + HIERARCHY_FIRST;

    /**
     * The event id indicating an ancestor-Container was resized.
     */
    public static final int ANCESTOR_RESIZED = 2 + HIERARCHY_FIRST;

    /**
     * Marks the last integer id for the range of ancestor event ids.
     */
    public static final int HIERARCHY_LAST = ANCESTOR_RESIZED;

    /**
     * A change flag indicates that the {@code HIERARCHY_CHANGED} event
     * was generated by a reparenting operation.
     */
    public static final int PARENT_CHANGED = 0x1;

    /**
     * A change flag indicates that the {@code HIERARCHY_CHANGED} event
     * was generated due to the changing of the hierarchy displayability.
     * To discern the
     * current displayability of the hierarchy, call the
     * {@code Component.isDisplayable} method. Displayability changes occur
     * in response to explicit or implicit calls of the
     * {@code Component.addNotify} and
     * {@code Component.removeNotify} methods.
     *
     * @see java.awt.Component#isDisplayable()
     * @see java.awt.Component#addNotify()
     * @see java.awt.Component#removeNotify()
     */
    public static final int DISPLAYABILITY_CHANGED = 0x2;

    /**
     * A change flag indicates that the {@code HIERARCHY_CHANGED} event
     * was generated due to the changing of the hierarchy showing state.
     * To discern the
     * current showing state of the hierarchy, call the
     * {@code Component.isShowing} method. Showing state changes occur
     * when either the displayability or visibility of the
     * hierarchy occurs. Visibility changes occur in response to explicit
     * or implicit calls of the {@code Component.show} and
     * {@code Component.hide} methods.
     *
     * @see java.awt.Component#isShowing()
     * @see java.awt.Component#addNotify()
     * @see java.awt.Component#removeNotify()
     * @see java.awt.Component#show()
     * @see java.awt.Component#hide()
     */
    public static final int SHOWING_CHANGED = 0x4;

    Component changed;
    Container changedParent;
    long      changeFlags;

    /**
     * Constructs an {@code HierarchyEvent} object to identify a
     * change in the {@code Component} hierarchy.
     * <p>This method throws an
     * {@code IllegalArgumentException} if {@code source}
     * is {@code null}.
     *
     * @param source          The {@code Component} object that
     *                        originated the event
     * @param id              An integer indicating the type of event.
     *                        For information on allowable values, see
     *                        the class description for {@link HierarchyEvent}
     * @param changed         The {@code Component} at the top of
     *                        the hierarchy which was changed
     * @param changedParent   The parent of the {@code changed} component.
     *                        This
     *                        may be the parent before or after the
     *                        change, depending on the type of change
     * @throws IllegalArgumentException if {@code source} is {@code null}
     * @see #getSource()
     * @see #getID()
     * @see #getChanged()
     * @see #getChangedParent()
     */
    public HierarchyEvent(Component source, int id, Component changed,
                          Container changedParent) {
        super(source, id);
        this.changed = changed;
        this.changedParent = changedParent;
    }

    /**
     * Constructs an {@code HierarchyEvent} object to identify
     * a change in the {@code Component} hierarchy.
     * <p> This method throws an
     * {@code IllegalArgumentException} if {@code source}
     * is {@code null}.
     *
     * @param source          The {@code Component} object that
     *                        originated the event
     * @param id              An integer indicating the type of event.
     *                        For information on allowable values, see
     *                        the class description for {@link HierarchyEvent}
     * @param changed         The {@code Component} at the top
     *                        of the hierarchy which was changed
     * @param changedParent   The parent of the {@code changed} component.
     *                        This
     *                        may be the parent before or after the
     *                        change, depending on the type of change
     * @param changeFlags     A bitmask which indicates the type(s) of
     *                        the {@code HIERARCHY_CHANGED} events
     *                        represented in this event object.
     *                        For information on allowable values, see
     *                        the class description for {@link HierarchyEvent}
     * @throws IllegalArgumentException if {@code source} is null
     * @see #getSource()
     * @see #getID()
     * @see #getChanged()
     * @see #getChangedParent()
     * @see #getChangeFlags()
     */
    public HierarchyEvent(Component source, int id, Component changed,
                          Container changedParent, long changeFlags) {
        super(source, id);
        this.changed = changed;
        this.changedParent = changedParent;
        this.changeFlags = changeFlags;
    }

    /**
     * Returns the originator of the event.
     *
     * @return the {@code Component} object that originated
     * the event, or {@code null} if the object is not a
     * {@code Component}.
     */
    public Component getComponent() {
        return (source instanceof Component) ? (Component)source : null;
    }

    /**
     * Returns the Component at the top of the hierarchy which was
     * changed.
     *
     * @return the changed Component
     */
    public Component getChanged() {
        return changed;
    }

    /**
     * Returns the parent of the Component returned by
     * {@code getChanged()}. For a HIERARCHY_CHANGED event where the
     * change was of type PARENT_CHANGED via a call to
     * {@code Container.add}, the parent returned is the parent
     * after the add operation. For a HIERARCHY_CHANGED event where
     * the change was of type PARENT_CHANGED via a call to
     * {@code Container.remove}, the parent returned is the parent
     * before the remove operation. For all other events and types,
     * the parent returned is the parent during the operation.
     *
     * @return the parent of the changed Component
     */
    public Container getChangedParent() {
        return changedParent;
    }

    /**
     * Returns a bitmask which indicates the type(s) of
     * HIERARCHY_CHANGED events represented in this event object.
     * The bits have been bitwise-ored together.
     *
     * @return the bitmask, or 0 if this is not an HIERARCHY_CHANGED
     * event
     */
    public long getChangeFlags() {
        return changeFlags;
    }

    /**
     * Returns a parameter string identifying this event.
     * This method is useful for event-logging and for debugging.
     *
     * @return a string identifying the event and its attributes
     */
    public String paramString() {
        String typeStr;
        switch(id) {
          case ANCESTOR_MOVED:
              typeStr = "ANCESTOR_MOVED ("+changed+","+changedParent+")";
              break;
          case ANCESTOR_RESIZED:
              typeStr = "ANCESTOR_RESIZED ("+changed+","+changedParent+")";
              break;
          case HIERARCHY_CHANGED: {
              typeStr = "HIERARCHY_CHANGED (";
              boolean first = true;
              if ((changeFlags & PARENT_CHANGED) != 0) {
                  first = false;
                  typeStr += "PARENT_CHANGED";
              }
              if ((changeFlags & DISPLAYABILITY_CHANGED) != 0) {
                  if (first) {
                      first = false;
                  } else {
                      typeStr += ",";
                  }
                  typeStr += "DISPLAYABILITY_CHANGED";
              }
              if ((changeFlags & SHOWING_CHANGED) != 0) {
                  if (first) {
                      first = false;
                  } else {
                      typeStr += ",";
                  }
                  typeStr += "SHOWING_CHANGED";
              }
              if (!first) {
                  typeStr += ",";
              }
              typeStr += changed + "," + changedParent + ")";
              break;
          }
          default:
              typeStr = "unknown type";
        }
        return typeStr;
    }
}