mxj~ Reference

Java in MSP



The mxj~ object (and its Max equivalent mxj) instantiate specially-written Java classes and acts as a Max-level peer object, passing data that originates in Max to the Java object and vice versa.


An mxj~ object producing noise


The form that an mxj~ object takes -- the number of inlets, outlets and the messages it understands -- is determined by the Java class that it instantiates. Unlike the Max mxj object, the mxj~ object is able to perform operations on signal vectors in an MSP processing chain. Using mxj~ requires that the host computer have a recent version of the Java Virtual Machine (JVM) installed. Macintosh users can ensure that they have the most up-to-date version of the JVM by running Software Update from the System Preferences. By default, Windows XP does not have a version of the JVM installed. As of the writing of this document the most recent version of the JVM can be downloaded from this link
Max includes a directory called "java-doc", which can be found on Windows machines at

C:\Program Files\Common Files\Cycling '74\java-doc

and on Macintosh machines at


The following important subdirectories are in the java-doc directory:

"classes" - contains the source code and class files of the example Java classes that are included with Max.

"help" - contains the help files that are associated with the example Java classes. Exploring these patches is a good, quick way to see how mxj~ has extended and will extend the Max universe.

"doc/tutorial" - contains a step-by-step tutorial that leads you through the process of creating your first Java class to the application of advanced mxj~ programming techniques. The tutorial is in HTML format.

"doc/api" - contains html files that specify mxj~ 's Application Programming Interface (API). These pages will serve as an invaluable resource when you are coding your own Java classes.

"doc/ide" - contains example projects for some of the Integrated Development Environments (IDEs) we think you may want to use to create Java classes.

"doc/mxj~ examples" - contains example classes for signal processing

"lib" - contains the code libraries that the mxj~ object uses to bridge the worlds of Max and Java.

In addition, a file named "" is also located in the java directory. This file allows you to specify which diretories should be in Java's classpath - a concept roughly analogous to the Max search path.


Java-class [symbol]

The mxj~ object must be given the name of a valid Java class as the first argument. The Java class file must exist somewhere within the classpath, and it must be a class that was designed for use with the mxj~ object (the class must subclass com.cycling74.max.MaxObject). The number of inlets that an instance of mxj~ creates and the messages that it will respond to are determined by declarations made in the peer Java class.

attributes [list]

The mxj~ object supports the definition of attributes within the Java code for a peer class. The attributes that are settable at the time of instantiation using the @ paradigm. For instance, if a particular class Foo defined an integer attribute called intBar, one could create an instance of the class with the attribute set to the value 74 by typing mxj~ Foo @intBar 74 in an object box.


Common Box Attributes



Function depends on Java class instantiated



input [int]
Function depends on Java class instantiated



input [float]
Function depends on Java class instantiated



input [list]
Function depends on Java class instantiated



input [list]
Function depends on Java class instantiated



benchmark-flag [int]
post-interval [int]
The word benchmark, followed by a zero or one and a number that specifies a posting interval (number of executions of the perform method), disables benchmarking the mxj~ object's perform method, posting into the Max Console. The default is zero (disabled)


Double-clicking with the mouse on the mxj~ object displays its contents as text in an editing window which the user can modify.



exception-flag [int]
The word exceptioncheck, followed by a zero or one, disables/enables Java exception checking in the mxj~ object's perform method. The default is zero (disabled).



attribute-name [list]
The word get followed by an attribute-name will post the attribute value in the Max window.


The viewsource message brings up a text editor window and loads the source code for the peer Java object. If the source code is not in the same directory as the peer class's .java file, a decompilation of the class file is attempted and the resulting decompiled source is presented. From within the editor window it's possible to make edits to the source, save the file, and recompile the class.


When a zap message is sent to an mxj~ object with Java peer class Foo, the next mxj~ object that's instantiated with the same peer Java class Foo (ie typing "mxj Foo" in an object box) will cause the class to reload itself from disk. This is most useful in a programming context: if one makes a change to and recompiles a new Foo.class the zap message allows one to create an instance of the new class without having to quit and restart the Max environment. Without sending the zap message Max would simply use the cached definition of the class that was loaded when a Foo object was instantiated prior to the changes being made.



The number of outlets that an instance of mxj~ creates is determined by declarations made in the constructor of the peer Java class. The furthest outlet to the right may or may not be an info outlet whose sole responsibility is to report information about the attributes when queried.

See Also

Name Description