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
   8  * particular file as subject to the "Classpath" exception as provided
   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  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  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 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 }
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