MidiSystem
class provides access to the installed MIDI
system resources, including devices such as synthesizers, sequencers, and
MIDI input and output ports. A typical simple MIDI application might
begin by invoking one or more MidiSystem
methods to learn
what devices are installed and to obtain the ones needed in that
application.
The class also has methods for reading files, streams, and URLs that
contain standard MIDI file data or soundbanks. You can query the
MidiSystem
for the format of a specified MIDI file.
You cannot instantiate a MidiSystem
; all the methods are
static.
Properties can be used to specify default MIDI devices. Both system properties and a properties file are considered. The properties file is "lib/sound.properties" in the JRE directory. If a property exists both as a system property and in the properties file, the system property takes precedence. If none is specified, a suitable default is chosen among the available devices. The syntax of the properties file is specified in Properties.load . The following table lists the available property keys and which methods consider them:
Property Key | Interface | Affected Method |
---|---|---|
javax.sound.midi.Receiver |
Receiver | #getReceiver |
javax.sound.midi.Sequencer |
Sequencer | #getSequencer |
javax.sound.midi.Synthesizer |
Synthesizer | #getSynthesizer |
javax.sound.midi.Transmitter |
Transmitter | #getTransmitter |
String
returned by the getName
method of MidiDevice.Info
.
Either the class name, or the device name may be omitted.
If only the class name is specified, the trailing hash mark
is optional.
If the provider class is specified, and it can be
successully retrieved from the installed providers,
the list of
MidiDevice.Info
objects is retrieved
from the provider. Otherwise, or when these devices
do not provide a subsequent match, the list is retrieved
from #getMidiDeviceInfo
to contain
all available MidiDevice.Info
objects.
If a device name is specified, the resulting list of
MidiDevice.Info
objects is searched:
the first one with a matching name, and whose
MidiDevice
implements the
respective interface, will be returned.
If no matching MidiDevice.Info
object
is found, or the device name is not specified,
the first suitable device from the resulting
list will be returned. For Sequencer and Synthesizer,
a device is suitable if it implements the respective
interface; whereas for Receiver and Transmitter, a device is
suitable if it
implements neither Sequencer nor Synthesizer and provides
at least one Receiver or Transmitter, respectively.
For example, the property javax.sound.midi.Receiver
with a value
"com.sun.media.sound.MidiProvider#SunMIDI1"
will have the following consequences when
getReceiver
is called:
if the class com.sun.media.sound.MidiProvider
exists
in the list of installed MIDI device providers,
the first Receiver
device with name
"SunMIDI1"
will be returned. If it cannot
be found, the first Receiver
from that provider
will be returned, regardless of name.
If there is none, the first Receiver
with name
"SunMIDI1"
in the list of all devices
(as returned by getMidiDeviceInfo
) will be returned,
or, if not found, the first Receiver
that can
be found in the list of all devices is returned.
If that fails, too, a MidiUnavailableException
is thrown.
The equals
method implements an equivalence relation
on non-null object references:
x
, x.equals(x)
should return
true
.
x
and y
, x.equals(y)
should return true
if and only if
y.equals(x)
returns true
.
x
, y
, and z
, if
x.equals(y)
returns true
and
y.equals(z)
returns true
, then
x.equals(z)
should return true
.
x
and y
, multiple invocations of
x.equals(y) consistently return true
or consistently return false
, provided no
information used in equals
comparisons on the
objects is modified.
x
,
x.equals(null)
should return false
.
The equals method for class Object
implements
the most discriminating possible equivalence relation on objects;
that is, for any non-null reference values x
and
y
, this method returns true
if and only
if x
and y
refer to the same object
(x == y
has the value true
).
Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.
File
. The
File
must point to valid MIDI file data for a file type
recognized by the system.
This operation can only succeed for files of a type which can be parsed by an installed file reader. It may fail with an InvalidMidiDataException even for valid files if no compatible file reader is installed. It will also fail with an InvalidMidiDataException if a compatible file reader is installed, but encounters errors while determining the file format.
This method and/or the code it invokes may need to read some data from
the stream to determine whether its data format is supported. The
implementation may therefore
need to mark the stream, read enough data to determine whether it is in
a supported format, and reset the stream's read pointer to its original
position. If the input stream does not permit this set of operations,
this method may fail with an IOException
.
This operation can only succeed for files of a type which can be parsed by an installed file reader. It may fail with an InvalidMidiDataException even for valid files if no compatible file reader is installed. It will also fail with an InvalidMidiDataException if a compatible file reader is installed, but encounters errors while determining the file format.
This operation can only succeed for files of a type which can be parsed by an installed file reader. It may fail with an InvalidMidiDataException even for valid files if no compatible file reader is installed. It will also fail with an InvalidMidiDataException if a compatible file reader is installed, but encounters errors while determining the file format.
If the system property
javax.sound.midi.Receiver
is defined or it is defined in the file "sound.properties",
it is used to identify the device that provides the default receiver.
For details, refer to the class description
.
If a suitable MIDI port is not available, the Receiver is
retrieved from an installed synthesizer.
If this method returns successfully, the MidiDevice
the
Receiver
belongs to is opened implicitly, if it is
not already open. It is possible to close an implicitly opened
device by calling close
on the returned Receiver
. All open Receiver
instances have to be closed in order to release system resources
hold by the MidiDevice
. For a
detailed description of open/close behaviour see the class
description of MidiDevice
.
File
.
The File
must point to valid MIDI file data
for a file type recognized by the system.
This operation can only succeed for files of a type which can be parsed
by an installed file reader. It may fail with an InvalidMidiDataException
even for valid files if no compatible file reader is installed. It
will also fail with an InvalidMidiDataException if a compatible file reader
is installed, but encounters errors while constructing the Sequence
object from the file data.
This method and/or the code it invokes may need to read some data
from the stream to determine whether
its data format is supported. The implementation may therefore
need to mark the stream, read enough data to determine whether it is in
a supported format, and reset the stream's read pointer to its original
position. If the input stream does not permit this set of operations,
this method may fail with an IOException
.
This operation can only succeed for files of a type which can be parsed
by an installed file reader. It may fail with an InvalidMidiDataException
even for valid files if no compatible file reader is installed. It
will also fail with an InvalidMidiDataException if a compatible file reader
is installed, but encounters errors while constructing the Sequence
object from the file data.
This operation can only succeed for files of a type which can be parsed
by an installed file reader. It may fail with an InvalidMidiDataException
even for valid files if no compatible file reader is installed. It
will also fail with an InvalidMidiDataException if a compatible file reader
is installed, but encounters errors while constructing the Sequence
object from the file data.
Sequencer
, connected to
a default device.
The returned Sequencer
instance is
connected to the default Synthesizer
,
as returned by #getSynthesizer
.
If there is no Synthesizer
available, or the default Synthesizer
cannot be opened, the sequencer
is connected
to the default Receiver
, as returned
by #getReceiver
.
The connection is made by retrieving a Transmitter
instance from the Sequencer
and setting its
Receiver
.
Closing and re-opening the sequencer will restore the
connection to the default device.
This method is equivalent to calling
getSequencer(true)
.
If the system property
javax.sound.midi.Sequencer
is defined or it is defined in the file "sound.properties",
it is used to identify the default sequencer.
For details, refer to the class description
.
Sequencer
, optionally
connected to a default device.
If connected
is true, the returned
Sequencer
instance is
connected to the default Synthesizer
,
as returned by #getSynthesizer
.
If there is no Synthesizer
available, or the default Synthesizer
cannot be opened, the sequencer
is connected
to the default Receiver
, as returned
by #getReceiver
.
The connection is made by retrieving a Transmitter
instance from the Sequencer
and setting its
Receiver
.
Closing and re-opening the sequencer will restore the
connection to the default device.
If connected
is false, the returned
Sequencer
instance is not connected, it
has no open Transmitters
. In order to
play the sequencer on a MIDI device, or a Synthesizer
,
it is necessary to get a Transmitter
and set its
Receiver
.
If the system property
javax.sound.midi.Sequencer
is defined or it is defined in the file "sound.properties",
it is used to identify the default sequencer.
For details, refer to the class description
.
Soundbank
by reading it from the specified
File
.
The File
must point to a valid MIDI soundbank file.Soundbank
by reading it from the specified URL.
The URL must point to a valid MIDI soundbank file.If the system property
javax.sound.midi.Synthesizer
is defined or it is defined in the file "sound.properties",
it is used to identify the default synthesizer.
For details, refer to the class description
.
If the system property
javax.sound.midi.Transmitter
is defined or it is defined in the file "sound.properties",
it is used to identify the device that provides the default transmitter.
For details, refer to the class description
.
If this method returns successfully, the MidiDevice
the
Transmitter
belongs to is opened implicitly, if it
is not already open. It is possible to close an implicitly
opened device by calling close
on the returned
Transmitter
. All open Transmitter
instances have to be closed in order to release system resources
hold by the MidiDevice
. For a detailed description
of open/close behaviour see the class description of MidiDevice
.
java.util.Hashtable
.
The general contract of hashCode
is:
hashCode
method on each of
the two objects must produce the same integer result.
As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.)
wait
methods.
The awakened thread will not be able to proceed until the current thread relinquishes the lock on this object. The awakened thread will compete in the usual manner with any other threads that might be actively competing to synchronize on this object; for example, the awakened thread enjoys no reliable privilege or disadvantage in being the next thread to lock this object.
This method should only be called by a thread that is the owner of this object's monitor. A thread becomes the owner of the object's monitor in one of three ways:
synchronized
statement
that synchronizes on the object.
Class,
by executing a
synchronized static method of that class.
Only one thread at a time can own an object's monitor.
wait
methods.
The awakened threads will not be able to proceed until the current thread relinquishes the lock on this object. The awakened threads will compete in the usual manner with any other threads that might be actively competing to synchronize on this object; for example, the awakened threads enjoy no reliable privilege or disadvantage in being the next thread to lock this object.
This method should only be called by a thread that is the owner
of this object's monitor. See the notify
method for a
description of the ways in which a thread can become the owner of
a monitor.
toString
method returns a string that
"textually represents" this object. The result should
be a concise but informative representation that is easy for a
person to read.
It is recommended that all subclasses override this method.
The toString
method for class Object
returns a string consisting of the name of the class of which the
object is an instance, the at-sign character `@
', and
the unsigned hexadecimal representation of the hash code of the
object. In other words, this method returns a string equal to the
value of:
getClass().getName() + '@' + Integer.toHexString(hashCode())
The current thread must own this object's monitor. The thread
releases ownership of this monitor and waits until another thread
notifies threads waiting on this object's monitor to wake up
either through a call to the notify
method or the
notifyAll
method. The thread then waits until it can
re-obtain ownership of the monitor and resumes execution.
As in the one argument version, interrupts and spurious wakeups are possible, and this method should always be used in a loop:
synchronized (obj) { while (<condition does not hold>) obj.wait(); ... // Perform action appropriate to condition }This method should only be called by a thread that is the owner of this object's monitor. See the
notify
method for a
description of the ways in which a thread can become the owner of
a monitor.The current thread must own this object's monitor.
This method causes the current thread (call it T) to place itself in the wait set for this object and then to relinquish any and all synchronization claims on this object. Thread T becomes disabled for thread scheduling purposes and lies dormant until one of four things happens:
A thread can also wake up without being notified, interrupted, or timing out, a so-called spurious wakeup. While this will rarely occur in practice, applications must guard against it by testing for the condition that should have caused the thread to be awakened, and continuing to wait if the condition is not satisfied. In other words, waits should always occur in loops, like this one:
synchronized (obj) { while (<condition does not hold>) obj.wait(timeout); ... // Perform action appropriate to condition }(For more information on this topic, see Section 3.2.3 in Doug Lea's "Concurrent Programming in Java (Second Edition)" (Addison-Wesley, 2000), or Item 50 in Joshua Bloch's "Effective Java Programming Language Guide" (Addison-Wesley, 2001).
If the current thread is interrupted by another thread while it is waiting, then an InterruptedException is thrown. This exception is not thrown until the lock status of this object has been restored as described above.
Note that the wait method, as it places the current thread into the wait set for this object, unlocks only this object; any other objects on which the current thread may be synchronized remain locked while the thread waits.
This method should only be called by a thread that is the owner
of this object's monitor. See the notify
method for a
description of the ways in which a thread can become the owner of
a monitor.
This method is similar to the wait
method of one
argument, but it allows finer control over the amount of time to
wait for a notification before giving up. The amount of real time,
measured in nanoseconds, is given by:
1000000*timeout+nanos
In all other respects, this method does the same thing as the method of one argument. In particular, wait(0, 0) means the same thing as wait(0).
The current thread must own this object's monitor. The thread releases ownership of this monitor and waits until either of the following two conditions has occurred:
notify
method
or the notifyAll
method.
timeout
milliseconds plus nanos
nanoseconds arguments, has
elapsed.
The thread then waits until it can re-obtain ownership of the monitor and resumes execution.
As in the one argument version, interrupts and spurious wakeups are possible, and this method should always be used in a loop:
synchronized (obj) { while (<condition does not hold>) obj.wait(timeout, nanos); ... // Perform action appropriate to condition }This method should only be called by a thread that is the owner of this object's monitor. See the
notify
method for a
description of the ways in which a thread can become the owner of
a monitor.