Java tutorial
/* * Copyright (c) 1999, 2018, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * 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. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ 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); } }