1 /*
2 * Copyright (c) 1998, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation. Oracle designates this
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9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
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24 */
25
26 package javax.sound.midi;
27
28 /**
29 * {@code MidiMessage} is the base class for MIDI messages. They include not
30 * only the standard MIDI messages that a synthesizer can respond to, but also
31 * "meta-events" that can be used by sequencer programs. There are meta-events
32 * for such information as lyrics, copyrights, tempo indications, time and key
33 * signatures, markers, etc. For more information, see the Standard MIDI Files
34 * 1.0 specification, which is part of the Complete MIDI 1.0 Detailed
35 * Specification published by the MIDI Manufacturer's Association
36 * (<a href = http://www.midi.org>http://www.midi.org</a>).
37 * <p>
38 * The base {@code MidiMessage} class provides access to three types of
39 * information about a MIDI message:
40 * <ul>
41 * <li>The messages's status byte</li>
42 * <li>The total length of the message in bytes (the status byte plus any data
43 * bytes)</li>
44 * <li>A byte array containing the complete message</li>
45 * </ul>
46 *
47 * {@code MidiMessage} includes methods to get, but not set, these values.
48 * Setting them is a subclass responsibility.
49 * <p>
50 * <a name="integersVsBytes"></a> The MIDI standard expresses MIDI data in
51 * bytes. However, because Java<sup>TM</sup> uses signed bytes, the Java Sound
52 * API uses integers instead of bytes when expressing MIDI data. For example,
53 * the {@link #getStatus()} method of {@code MidiMessage} returns MIDI status
54 * bytes as integers. If you are processing MIDI data that originated outside
55 * Java Sound and now is encoded as signed bytes, the bytes can be
56 * converted to integers using this conversion:
57 *
58 * <center>{@code int i = (int)(byte & 0xFF)}</center>
59 * <p>
60 * If you simply need to pass a known MIDI byte value as a method parameter, it
61 * can be expressed directly as an integer, using (for example) decimal or
62 * hexadecimal notation. For instance, to pass the "active sensing" status byte
63 * as the first argument to ShortMessage's
64 * {@link ShortMessage#setMessage(int) setMessage(int)} method, you can express
65 * it as 254 or 0xFE.
66 *
67 * @author David Rivas
68 * @author Kara Kytle
69 * @see Track
70 * @see Sequence
71 * @see Receiver
72 */
73 public abstract class MidiMessage implements Cloneable {
74
75 /**
76 * The MIDI message data. The first byte is the status byte for the message;
77 * subsequent bytes up to the length of the message are data bytes for this
78 * message.
79 *
80 * @see #getLength
81 */
82 protected byte[] data;
83
84 /**
85 * The number of bytes in the MIDI message, including the status byte and
86 * any data bytes.
87 *
88 * @see #getLength
89 */
90 protected int length = 0;
91
92 /**
93 * Constructs a new {@code MidiMessage}. This protected constructor is
94 * called by concrete subclasses, which should ensure that the data array
95 * specifies a complete, valid MIDI message.
96 *
97 * @param data an array of bytes containing the complete message. The
98 * message data may be changed using the {@code setMessage} method.
99 * @see #setMessage
100 */
101 protected MidiMessage(byte[] data) {
102 this.data = data;
103 if (data != null) {
104 this.length = data.length;
105 }
106 }
107
108 /**
109 * Sets the data for the MIDI message. This protected method is called by
110 * concrete subclasses, which should ensure that the data array specifies a
111 * complete, valid MIDI message.
112 *
113 * @param data the data bytes in the MIDI message
114 * @param length the number of bytes in the data byte array
115 * @throws InvalidMidiDataException if the parameter values do not specify a
116 * valid MIDI meta message
117 */
118 protected void setMessage(byte[] data, int length)
119 throws InvalidMidiDataException {
120 if (length < 0 || (length > 0 && length > data.length)) {
121 throw new IndexOutOfBoundsException(
122 "length out of bounds: " + length);
123 }
124 this.length = length;
125
126 if (this.data == null || this.data.length < this.length) {
127 this.data = new byte[this.length];
128 }
129 System.arraycopy(data, 0, this.data, 0, length);
130 }
131
132 /**
133 * Obtains the MIDI message data. The first byte of the returned byte array
134 * is the status byte of the message. Any subsequent bytes up to the length
135 * of the message are data bytes. The byte array may have a length which is
136 * greater than that of the actual message; the total length of the message
137 * in bytes is reported by the {@link #getLength} method.
138 *
139 * @return the byte array containing the complete {@code MidiMessage} data
140 */
141 public byte[] getMessage() {
142 byte[] returnedArray = new byte[length];
143 System.arraycopy(data, 0, returnedArray, 0, length);
144 return returnedArray;
145 }
146
147 /**
148 * Obtains the status byte for the MIDI message. The status "byte" is
149 * represented as an integer; see the
150 * <a href="#integersVsBytes">discussion</a> in the {@code MidiMessage}
151 * class description.
152 *
153 * @return the integer representation of this event's status byte
154 */
155 public int getStatus() {
156 if (length > 0) {
157 return (data[0] & 0xFF);
158 }
159 return 0;
160 }
161
162 /**
163 * Obtains the total length of the MIDI message in bytes. A MIDI message
164 * consists of one status byte and zero or more data bytes. The return value
165 * ranges from 1 for system real-time messages, to 2 or 3 for channel
166 * messages, to any value for meta and system exclusive messages.
167 *
168 * @return the length of the message in bytes
169 */
170 public int getLength() {
171 return length;
172 }
173
174 /**
175 * Creates a new object of the same class and with the same contents as this
176 * object.
177 *
178 * @return a clone of this instance
179 */
180 public abstract Object clone();
181 }