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Class MidiMessage

All Implemented Interfaces:
Cloneable
Direct Known Subclasses:
MetaMessage, ShortMessage, SysexMessage 
public abstract class MidiMessage
extends Object
implements Cloneable

MidiMessage is the base class for MIDI messages. They include not only the standard MIDI messages that a synthesizer can respond to, but also "meta-events" that can be used by sequencer programs. There are 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 (http://www.midi.org).

The base MidiMessage class provides access to three types of information about a MIDI message:

  • The messages's status byte
  • The total length of the message in bytes (the status byte plus any data bytes)
  • A byte array containing the complete message
MidiMessage includes methods to get, but not set, these values. Setting them is a subclass responsibility.

The MIDI standard expresses MIDI data in bytes. However, because JavaTM uses signed bytes, the Java Sound API uses integers instead of bytes when expressing MIDI data. For example, the getStatus() method of MidiMessage returns MIDI status bytes as integers. If you are processing MIDI data that originated outside Java Sound and now is encoded as signed bytes, the bytes can can be converted to integers using this conversion:

int i = (int)(byte & 0xFF)

If you simply need to pass a known MIDI byte value as a method parameter, it can be expressed directly as an integer, using (for example) decimal or hexadecimal notation. For instance, to pass the "active sensing" status byte as the first argument to ShortMessage's setMessage(int) method, you can express it as 254 or 0xFE.

See Also:
Track, Sequence, Receiver

Fields

data

protected byte[] data

The MIDI message data. The first byte is the status byte for the message; subsequent bytes up to the length of the message are data bytes for this message.

See Also:
getLength()

length

protected int length

The number of bytes in the MIDI message, including the status byte and any data bytes.

See Also:
getLength()

Constructors

MidiMessage

protected MidiMessage(byte[] data)

Constructs a new MidiMessage. This protected constructor is called by concrete subclasses, which should ensure that the data array specifies a complete, valid MIDI message.

Parameters:
data - an array of bytes containing the complete message. The message data may be changed using the setMessage method.
See Also:
setMessage(byte[], int)

Methods

setMessage

protected void setMessage(byte[] data,
                          int length)
                   throws InvalidMidiDataException

Sets the data for the MIDI message. This protected method is called by concrete subclasses, which should ensure that the data array specifies a complete, valid MIDI message.

Parameters:
data - the data bytes in the MIDI message
length - the number of bytes in the data byte array
Throws:
InvalidMidiDataException - if the parameter values do not specify a valid MIDI meta message

getMessage

public byte[] getMessage()

Obtains the MIDI message data. The first byte of the returned byte array is the status byte of the message. Any subsequent bytes up to the length of the message are data bytes. The byte array may have a length which is greater than that of the actual message; the total length of the message in bytes is reported by the getLength() method.

Returns:
the byte array containing the complete MidiMessage data

getStatus

public int getStatus()

Obtains the status byte for the MIDI message. The status "byte" is represented as an integer; see the discussion in the MidiMessage class description.

Returns:
the integer representation of this event's status byte

getLength

public int getLength()

Obtains the total length of the MIDI message in bytes. A MIDI message consists of one status byte and zero or more data bytes. The return value ranges from 1 for system real-time messages, to 2 or 3 for channel messages, to any value for meta and system exclusive messages.

Returns:
the length of the message in bytes

clone

public abstract Object clone()

Creates a new object of the same class and with the same contents as this object.

Overrides:
clone in class Object
Returns:
a clone of this instance.
See Also:
Cloneable

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Documentation extracted from Debian's OpenJDK Development Kit package.
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