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25
26package 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
42 *   <li>The total length of the message in bytes (the status byte plus any data
43 *   bytes)
44 *   <li>A byte array containing the complete message
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 id="integersVsBytes"></a>The MIDI standard expresses MIDI data in bytes.
51 * However, because Java&trade; uses signed bytes, the Java Sound API uses
52 * integers instead of bytes when expressing MIDI data. For example, the
53 * {@link #getStatus()} method of {@code MidiMessage} returns MIDI status bytes
54 * as integers. If you are processing MIDI data that originated outside Java
55 * Sound and now is encoded as signed bytes, the bytes can be converted to
56 * integers using this conversion:
57 * <p style="text-align:center">
58 * {@code int i = (int)(byte & 0xFF)}
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 {@code 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 */
73public 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    @Override
181    public abstract Object clone();
182}
183