1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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10 *
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12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
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24 */
25
26 package javax.sound.midi;
27
28 /**
29 * <code>MidiMessage</code> is the base class for MIDI messages. They include
30 * not 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 1.0
34 * specification, which is part of the Complete MIDI 1.0 Detailed Specification
35 * 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</code> 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 bytes)</li>
43 * <li>A byte array containing the complete message</li>
44 * </ul>
45 *
46 * <code>MidiMessage</code> includes methods to get, but not set, these values.
47 * Setting them is a subclass responsibility.
48 * <p>
49 * <a name="integersVsBytes"></a>
50 * The MIDI standard expresses MIDI data in bytes. However, because
51 * Java<sup>TM</sup> uses signed bytes, the Java Sound API uses integers
52 * instead of bytes when expressing MIDI data. For example, the
53 * {@link #getStatus()} method of
54 * <code>MidiMessage</code> returns MIDI status bytes as integers. If you are
55 * processing MIDI data that originated outside Java Sound and now
56 * is encoded as signed bytes, the bytes can
57 * can be converted to integers using this conversion:
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,
61 * it can be expressed directly as an integer, using (for example) decimal or
62 * hexidecimal 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)}
65 * method, you can express it as 254 or 0xFE.
66 *
67 * @see Track
68 * @see Sequence
69 * @see Receiver
70 *
71 * @author David Rivas
72 * @author Kara Kytle
73 */
74
75 public abstract class MidiMessage implements Cloneable {
76
77 // Instance variables
78
79 /**
80 * The MIDI message data. The first byte is the status
81 * byte for the message; subsequent bytes up to the length
82 * of the message are data bytes for this message.
83 * @see #getLength
84 */
85 protected byte[] data;
86
87
88 /**
89 * The number of bytes in the MIDI message, including the
90 * status byte and any data bytes.
91 * @see #getLength
92 */
93 protected int length = 0;
94
95
96 /**
97 * Constructs a new <code>MidiMessage</code>. This protected
98 * constructor is called by concrete subclasses, which should
99 * ensure that the data array specifies a complete, valid MIDI
100 * message.
101 *
102 * @param data an array of bytes containing the complete message.
103 * The message data may be changed using the <code>setMessage</code>
104 * method.
105 *
106 * @see #setMessage
107 */
108 protected MidiMessage(byte[] data) {
109 this.data = data;
110 if (data != null) {
111 this.length = data.length;
112 }
113 }
114
115
116 /**
117 * Sets the data for the MIDI message. This protected
118 * method is called by concrete subclasses, which should
119 * ensure that the data array specifies a complete, valid MIDI
120 * message.
121 *
122 * @param data the data bytes in the MIDI message
123 * @param length the number of bytes in the data byte array
124 * @throws InvalidMidiDataException if the parameter values do not specify a valid MIDI meta message
125 */
126 protected void setMessage(byte[] data, int length) throws InvalidMidiDataException {
127 if (length < 0 || (length > 0 && length > data.length)) {
128 throw new IndexOutOfBoundsException("length out of bounds: "+length);
129 }
130 this.length = length;
131
132 if (this.data == null || this.data.length < this.length) {
133 this.data = new byte[this.length];
134 }
135 System.arraycopy(data, 0, this.data, 0, length);
136 }
137
138
139 /**
140 * Obtains the MIDI message data. The first byte of the returned byte
141 * array is the status byte of the message. Any subsequent bytes up to
142 * the length of the message are data bytes. The byte array may have a
143 * length which is greater than that of the actual message; the total
144 * length of the message in bytes is reported by the <code>{@link #getLength}</code>
145 * method.
146 *
147 * @return the byte array containing the complete <code>MidiMessage</code> data
148 */
149 public byte[] getMessage() {
150 byte[] returnedArray = new byte[length];
151 System.arraycopy(data, 0, returnedArray, 0, length);
152 return returnedArray;
153 }
154
155
156 /**
157 * Obtains the status byte for the MIDI message. The status "byte" is
158 * represented as an integer; see the
159 * <a href="#integersVsBytes">discussion</a> in the
160 * <code>MidiMessage</code> class description.
161 *
162 * @return the integer representation of this event's status byte
163 */
164 public int getStatus() {
165 if (length > 0) {
166 return (data[0] & 0xFF);
167 }
168 return 0;
169 }
170
171
172 /**
173 * Obtains the total length of the MIDI message in bytes. A
174 * MIDI message consists of one status byte and zero or more
175 * data bytes. The return value ranges from 1 for system real-time messages,
176 * to 2 or 3 for channel messages, to any value for meta and system
177 * exclusive messages.
178 *
179 * @return the length of the message in bytes
180 */
181 public int getLength() {
182 return length;
183 }
184
185
186 /**
187 * Creates a new object of the same class and with the same contents
188 * as this object.
189 * @return a clone of this instance.
190 */
191 public abstract Object clone();
192 }