The MetaMessage.java Java example source code
/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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* published by the Free Software Foundation. Oracle designates this
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*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
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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).
*
* <p>
* When data is being transported using MIDI wire protocol,
* a <code>{@link ShortMessage} with the status value 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.
*
* @see MetaEventListener
*
* @author David Rivas
* @author Kara Kytle
*/
public class MetaMessage extends MidiMessage {
// Status byte defines
/**
* Status byte for <code>MetaMessage (0xFF, or 255), which is used
* in MIDI files. It has the same value as SYSTEM_RESET, which
* is used in the real-time "MIDI wire" protocol.
* @see MidiMessage#getStatus
*/
public static final int META = 0xFF; // 255
// Instance variables
/**
* 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 <code>{@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 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
*/
public Object clone() {
byte[] newData = new byte[length];
System.arraycopy(data, 0, newData, 0, newData.length);
MetaMessage event = new MetaMessage(newData);
return event;
}
// HELPER METHODS
private int getVarIntLength(long value) {
int length = 0;
do {
value = value >> 7;
length++;
} while (value > 0);
return length;
}
private final static 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);
}
}
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