MetaMessage.java

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package javax.sound.midi;

/**
 * A {@code MetaMessage} is a {@link MidiMessage} that is not meaningful to
 * synthesizers, but that can be stored in a MIDI file and interpreted by a
 * sequencer program. (See the discussion in the {@code MidiMessage} class
 * description.) The Standard MIDI Files specification defines various types of
 * meta-events, such as sequence number, lyric, cue point, and set tempo. There
 * are also meta-events for such information as lyrics, copyrights, tempo
 * indications, time and key signatures, markers, etc. For more information, see
 * the Standard MIDI Files 1.0 specification, which is part of the Complete MIDI
 * 1.0 Detailed Specification published by the MIDI Manufacturer's Association
 * (<a href = http://www.midi.org>http://www.midi.org</a>).
 * <p>
 * When data is being transported using MIDI wire protocol, a
 * {@link ShortMessage} with the status value {@code 0xFF} represents a system
 * reset message. In MIDI files, this same status value denotes a
 * {@code MetaMessage}. The types of meta-message are distinguished from each
 * other by the first byte that follows the status byte {@code 0xFF}. The
 * subsequent bytes are data bytes. As with system exclusive messages, there are
 * an arbitrary number of data bytes, depending on the type of
 * {@code MetaMessage}.
 *
 * @author David Rivas
 * @author Kara Kytle
 * @see MetaEventListener
 */
public class MetaMessage extends MidiMessage {

    /**
     * Status byte for {@code MetaMessage} (0xFF, or 255), which is used in MIDI
     * files. It has the same value as {@link ShortMessage#SYSTEM_RESET}, which
     * is used in the real-time "MIDI wire" protocol.
     *
     * @see MidiMessage#getStatus
     */
    public static final int META = 0xFF; // 255

    /**
     * The length of the actual message in the data array. This is used to
     * determine how many bytes of the data array is the message, and how many
     * are the status byte, the type byte, and the variable-length-int
     * describing the length of the message.
     */
    private int dataLength = 0;

    /**
     * Constructs a new {@code MetaMessage}. The contents of the message are not
     * set here; use {@link #setMessage(int, byte[], int) setMessage} to set
     * them subsequently.
     */
    public MetaMessage() {
        // Default meta message data: just the META status byte value
        this(new byte[]{(byte) META, 0});
    }

    /**
     * Constructs a new {@code MetaMessage} and sets the message parameters. The
     * contents of the message can be changed by using the {@code setMessage}
     * method.
     *
     * @param  type meta-message type (must be less than 128)
     * @param  data the data bytes in the MIDI message
     * @param  length an amount of bytes in the {@code data} byte array; it
     *         should be non-negative and less than or equal to
     *         {@code data.length}
     * @throws InvalidMidiDataException if the parameter values do not specify a
     *         valid MIDI meta message
     * @see #setMessage(int, byte[], int)
     * @see #getType()
     * @see #getData()
     * @since 1.7
     */
    public MetaMessage(int type, byte[] data, int length)
            throws InvalidMidiDataException {
        super(null);
        setMessage(type, data, length); // can throw InvalidMidiDataException
    }

    /**
     * Constructs a new {@code MetaMessage}.
     *
     * @param  data an array of bytes containing the complete message. The
     *         message data may be changed using the {@code setMessage} method.
     * @see #setMessage
     */
    protected MetaMessage(byte[] data) {
        super(data);
        //$$fb 2001-10-06: need to calculate dataLength. Fix for bug #4511796
        if (data.length>=3) {
            dataLength=data.length-3;
            int pos=2;
            while (pos<data.length && (data[pos] & 0x80)!=0) {
                dataLength--; pos++;
            }
        }
    }

    /**
     * Sets the message parameters for a {@code MetaMessage}. Since only one
     * status byte value, {@code 0xFF}, is allowed for meta-messages, it does
     * not need to be specified here. Calls to
     * {@link MidiMessage#getStatus getStatus} return {@code 0xFF} for all
     * meta-messages.
     * <p>
     * The {@code type} argument should be a valid value for the byte that
     * follows the status byte in the {@code MetaMessage}. The {@code data}
     * argument should contain all the subsequent bytes of the
     * {@code MetaMessage}. In other words, the byte that specifies the type of
     * {@code MetaMessage} is not considered a data byte.
     *
     * @param  type meta-message type (must be less than 128)
     * @param  data the data bytes in the MIDI message
     * @param  length the number of bytes in the {@code data} byte array
     * @throws InvalidMidiDataException if the parameter values do not specify a
     *         valid MIDI meta message
     */
    public void setMessage(int type, byte[] data, int length) throws InvalidMidiDataException {

        if (type >= 128 || type < 0) {
            throw new InvalidMidiDataException("Invalid meta event with type " + type);
        }
        if ((length > 0 && length > data.length) || length < 0) {
            throw new InvalidMidiDataException("length out of bounds: "+length);
        }

        this.length = 2 + getVarIntLength(length) + length;
        this.dataLength = length;
        this.data = new byte[this.length];
        this.data[0] = (byte) META;        // status value for MetaMessages (meta events)
        this.data[1] = (byte) type;        // MetaMessage type
        writeVarInt(this.data, 2, length); // write the length as a variable int
        if (length > 0) {
            System.arraycopy(data, 0, this.data, this.length - this.dataLength, this.dataLength);
        }
    }

    /**
     * Obtains the type of the {@code MetaMessage}.
     *
     * @return an integer representing the {@code MetaMessage} type
     */
    public int getType() {
        if (length>=2) {
            return data[1] & 0xFF;
        }
        return 0;
    }

    /**
     * Obtains a copy of the data for the meta message. The returned array of
     * bytes does not include the status byte or the message length data. The
     * length of the data for the meta message is the length of the array. Note
     * that the length of the entire message includes the status byte and the
     * meta message type byte, and therefore may be longer than the returned
     * array.
     *
     * @return array containing the meta message data
     * @see MidiMessage#getLength
     */
    public byte[] getData() {
        byte[] returnedArray = new byte[dataLength];
        System.arraycopy(data, (length - dataLength), returnedArray, 0, dataLength);
        return returnedArray;
    }

    /**
     * Creates a new object of the same class and with the same contents as this
     * object.
     *
     * @return a clone of this instance
     */
    @Override
    public Object clone() {
        byte[] newData = new byte[length];
        System.arraycopy(data, 0, newData, 0, newData.length);
        return new MetaMessage(newData);
    }

    // HELPER METHODS

    private int getVarIntLength(long value) {
        int length = 0;
        do {
            value = value >> 7;
            length++;
        } while (value > 0);
        return length;
    }

    private static final long mask = 0x7F;

    private void writeVarInt(byte[] data, int off, long value) {
        int shift=63; // number of bitwise left-shifts of mask
        // first screen out leading zeros
        while ((shift > 0) && ((value & (mask << shift)) == 0)) shift-=7;
        // then write actual values
        while (shift > 0) {
            data[off++]=(byte) (((value & (mask << shift)) >> shift) | 0x80);
            shift-=7;
        }
        data[off] = (byte) (value & mask);
    }
}