LineEvent.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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package javax.sound.sampled;

import java.io.Serial;
import java.util.EventObject;

/**
 * The {@code LineEvent} class encapsulates information that a line sends its
 * listeners whenever the line opens, closes, starts, or stops. Each of these
 * four state changes is represented by a corresponding type of event. A
 * listener receives the event as a parameter to its
 * {@link LineListener#update update} method. By querying the event, the
 * listener can learn the type of event, the line responsible for the event, and
 * how much data the line had processed when the event occurred.
 * <p>
 * Although this class implements Serializable, attempts to serialize a
 * {@code LineEvent} object will fail.
 *
 * @author Kara Kytle
 * @see Line
 * @see LineListener#update
 * @since 1.3
 *
 * @serial exclude
 */
public class LineEvent extends EventObject {

    /**
     * Use serialVersionUID from JDK 1.3 for interoperability.
     */
    @Serial
    private static final long serialVersionUID = -1274246333383880410L;

    /**
     * The kind of line event ({@code OPEN}, {@code CLOSE}, {@code START}, or
     * {@code STOP}).
     *
     * @see #getType
     * @serial
     */
    @SuppressWarnings("serial") // Not statically typed as Serializable
    private final Type type;

    /**
     * The media position when the event occurred, expressed in sample frames.
     * Note that this field is only relevant to certain events generated by data
     * lines, such as {@code START} and {@code STOP}. For events generated by
     * lines that do not count sample frames, and for any other events for which
     * this value is not known, the position value should be
     * {@link AudioSystem#NOT_SPECIFIED}.
     *
     * @see #getFramePosition
     * @serial
     */
    private final long position;

    /**
     * Constructs a new event of the specified type, originating from the
     * specified line.
     *
     * @param  line the source of this event
     * @param  type the event type ({@code OPEN}, {@code CLOSE}, {@code START},
     *         or {@code STOP})
     * @param  position the number of sample frames that the line had already
     *         processed when the event occurred, or
     *         {@link AudioSystem#NOT_SPECIFIED}
     * @throws IllegalArgumentException if {@code line} is {@code null}
     */
    public LineEvent(Line line, Type type, long position) {

        super(line);
        this.type = type;
        this.position = position;
    }

    /**
     * Obtains the audio line that is the source of this event.
     *
     * @return the line responsible for this event
     */
    public final Line getLine() {
        return (Line)getSource();
    }

    /**
     * Obtains the event's type.
     *
     * @return this event's type ({@link Type#OPEN}, {@link Type#CLOSE},
     *         {@link Type#START}, or {@link Type#STOP})
     */
    public final Type getType() {
        return type;
    }

    /**
     * Obtains the position in the line's audio data when the event occurred,
     * expressed in sample frames. For example, if a source line had already
     * played back 14 sample frames at the time it was paused, the pause event
     * would report the line's position as 14. The next frame to be processed
     * would be frame number 14 using zero-based numbering, or 15 using
     * one-based numbering.
     * <p>
     * Note that this field is relevant only to certain events generated by data
     * lines, such as {@code START} and {@code STOP}. For events generated by
     * lines that do not count sample frames, and for any other events for which
     * this value is not known, the position value should be
     * {@link AudioSystem#NOT_SPECIFIED}.
     *
     * @return the line's position as a sample frame number
     */
    /*
     * $$kk: 04.20.99: note to myself: should make sure our implementation is
     * consistent with this.
     * which is a reasonable definition....
     */
    public final long getFramePosition() {
        return position;
    }

    /**
     * Returns a string representation of the event.
     *
     * @return a string representation of the event
     */
    @Override
    public String toString() {
        return String.format("%s event from line %s", type, getLine());
    }

    /**
     * The LineEvent.Type inner class identifies what kind of event occurred on
     * a line. Static instances are provided for the common types (OPEN, CLOSE,
     * START, and STOP).
     *
     * @see LineEvent#getType()
     */
    public static class Type {

        /**
         * Type name.
         */
        private final String name;

        /**
         * Constructs a new event type.
         *
         * @param  name name of the type
         */
        protected Type(String name) {
            this.name = name;
        }

        //$$fb 2002-11-26: fix for 4695001: SPEC: description of equals() method contains typo

        /**
         * Indicates whether the specified object is equal to this event type,
         * returning {@code true} if the objects are the same.
         *
         * @param  obj the reference object with which to compare
         * @return {@code true} if the specified object is equal to this event
         *         type; {@code false} otherwise
         */
        @Override
        public final boolean equals(Object obj) {
            return super.equals(obj);
        }

        /**
         * Returns a hash code value for this event type.
         *
         * @return a hash code value for this event type
         */
        @Override
        public final int hashCode() {
            return super.hashCode();
        }

        /**
         * Returns type's name as the string representation of the event type.
         *
         * @return a string representation of the event type
         */
        @Override
        public String toString() {
            return name;
        }

        // LINE EVENT TYPE DEFINES

        /**
         * A type of event that is sent when a line opens, reserving system
         * resources for itself.
         *
         * @see #CLOSE
         * @see Line#open
         */
        public static final Type OPEN = new Type("Open");

        /**
         * A type of event that is sent when a line closes, freeing the system
         * resources it had obtained when it was opened.
         *
         * @see #OPEN
         * @see Line#close
         */
        public static final Type CLOSE = new Type("Close");

        /**
         * A type of event that is sent when a line begins to engage in active
         * input or output of audio data in response to a
         * {@link DataLine#start start} request.
         *
         * @see #STOP
         * @see DataLine#start
         */
        public static final Type START = new Type("Start");

        /**
         * A type of event that is sent when a line ceases active input or
         * output of audio data in response to a {@link DataLine#stop stop}
         * request, or because the end of media has been reached.
         *
         * @see #START
         * @see DataLine#stop
         */
        public static final Type STOP = new Type("Stop");

        /**
         * A type of event that is sent when a line ceases to engage in active
         * input or output of audio data because the end of media has been
         * reached.
         */
        /*
         * ISSUE: we may want to get rid of this. Is JavaSound responsible for
         * reporting this??
         *
         * [If it's decided to keep this API, the docs will need to be updated
         * to include mention of EOM events elsewhere.]
         */
        //public static final Type EOM  = new Type("EOM");

        /**
         * A type of event that is sent when a line begins to engage in active
         * input or output of audio data. Examples of when this happens are when
         * a source line begins or resumes writing data to its mixer, and when a
         * target line begins or resumes reading data from its mixer.
         *
         * @see #STOP
         * @see SourceDataLine#write
         * @see TargetDataLine#read
         * @see DataLine#start
         */
        //public static final Type ACTIVE       = new Type("ACTIVE");

        /**
         * A type of event that is sent when a line ceases active input or
         * output of audio data.
         *
         * @see #START
         * @see DataLine#stop
         */
        //public static final Type INACTIVE     = new Type("INACTIVE");
    }
}