src/java.desktop/share/classes/java/awt/event/ContainerEvent.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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package java.awt.event;

import java.awt.Component;
import java.awt.Container;
import java.io.Serial;

/**
 * A low-level event which indicates that a container's contents
 * changed because a component was added or removed.
 * <P>
 * Container events are provided for notification purposes ONLY;
 * The AWT will automatically handle changes to the containers
 * contents internally so that the program works properly regardless of
 * whether the program is receiving these events or not.
 * <P>
 * This low-level event is generated by a container object (such as a
 * Panel) when a component is added to it or removed from it.
 * The event is passed to every {@code ContainerListener}
 * or {@code ContainerAdapter} object which registered to receive such
 * events using the component's {@code addContainerListener} method.
 * ({@code ContainerAdapter} objects implement the
 * {@code ContainerListener} interface.) Each such listener object
 * gets this {@code ContainerEvent} when the event occurs.
 * <p>
 * An unspecified behavior will be caused if the {@code id} parameter
 * of any particular {@code ContainerEvent} instance is not
 * in the range from {@code CONTAINER_FIRST} to {@code CONTAINER_LAST}.
 *
 * @see ContainerAdapter
 * @see ContainerListener
 * @see <a href="https://docs.oracle.com/javase/tutorial/uiswing/events/containerlistener.html">Tutorial: Writing a Container Listener</a>
 *
 * @author Tim Prinzing
 * @author Amy Fowler
 * @since 1.1
 */
public class ContainerEvent extends ComponentEvent {

    /**
     * The first number in the range of ids used for container events.
     */
    public static final int CONTAINER_FIRST             = 300;

    /**
     * The last number in the range of ids used for container events.
     */
    public static final int CONTAINER_LAST              = 301;

   /**
     * This event indicates that a component was added to the container.
     */
    public static final int COMPONENT_ADDED     = CONTAINER_FIRST;

    /**
     * This event indicates that a component was removed from the container.
     */
    public static final int COMPONENT_REMOVED = 1 + CONTAINER_FIRST;

    /**
     * The non-null component that is being added or
     * removed from the Container.
     *
     * @serial
     * @see #getChild()
     */
    Component child;

    /**
     * Use serialVersionUID from JDK 1.1 for interoperability.
     */
    @Serial
    private static final long serialVersionUID = -4114942250539772041L;

    /**
     * Constructs a {@code ContainerEvent} object.
     * <p> This method throws an
     * {@code IllegalArgumentException} if {@code source}
     * is {@code null}.
     *
     * @param source The {@code Component} object (container)
     *               that originated the event
     * @param id     An integer indicating the type of event.
     *                     For information on allowable values, see
     *                     the class description for {@link ContainerEvent}
     * @param child  the component that was added or removed
     * @throws IllegalArgumentException if {@code source} is null
     * @see #getContainer()
     * @see #getID()
     * @see #getChild()
     */
    public ContainerEvent(Component source, int id, Component child) {
        super(source, id);
        this.child = child;
    }

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

    /**
     * Returns the component that was affected by the event.
     *
     * @return the Component object that was added or removed
     */
    public Component getChild() {
        return child;
    }

    /**
     * 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 COMPONENT_ADDED:
              typeStr = "COMPONENT_ADDED";
              break;
          case COMPONENT_REMOVED:
              typeStr = "COMPONENT_REMOVED";
              break;
          default:
              typeStr = "unknown type";
        }
        return typeStr + ",child="+child.getName();
    }
}