External Interfaces/API

Invoking Methods on Java Objects

This section explains how to invoke an object's methods in MATLAB. It also covers how to obtain information related to the methods that you're using and how MATLAB handles certain types of nonstandard situations.

This section addresses the following topics:

• Using Java and MATLAB Calling Syntax
• Invoking Static Methods on Java Classes
• Obtaining Information About Methods
• Java Methods That Affect MATLAB Commands
• How MATLAB Handles Undefined Methods
• How MATLAB Handles Java Exceptions

Using Java and MATLAB Calling Syntax

To call methods on Java objects, you can use the Java syntax

• object.method(arg1,...,argn)
  

In the following example, frame is the java.awt.Frame object created above, and getTitle and setTitle are methods of that object.

• frame.setTitle('Sample Frame')
  
  title = frame.getTitle
  title = 
  Sample Frame
  

Alternatively, you can call Java object (nonstatic) methods with the MATLAB syntax

• method(object, arg1,...,argn)
  

With MATLAB syntax, the java.awt.Frame example above becomes

• setTitle(frame, 'Sample Frame')
  
  title = getTitle(frame)
  title = 
  Sample Frame
  

All of the programming examples in this chapter contain invocations of Java object methods. For example, the code for Reading a URL contains a call, using MATLAB syntax, to the openStream method on a java.net.URL object, url.

• is = openStream(url)
  

In another example, the code for Example - Creating and Using a Phone Book contains a call, using Java syntax, to the load method on a java.utils.Properties object, pb_htable.

• pb_htable.load(FIS);
  

Using the javaMethod Function on Nonstatic Methods

Under certain circumstances, you may need to use the javaMethod function to call a Java method. The following syntax invokes the method, method_name, on Java object J with the argument list that matches x1,...,xn. This returns the value X.

• X = javaMethod('method_name',J,x1,...,xn);
  

For example, to call the startsWith method on a java.lang.String object passing one argument, use

• gAddress = java.lang.String('Four score and seven years ago');
  str = java.lang.String('Four score');
  
  javaMethod('startsWith', gAddress, str)
  ans =
       1
  

Using the javaMethod function enables you to

• Use methods that have names that exceed the maximum length of a MATLAB identifier. (Call the namelengthmax function to obtain the maximum identifier length.)
• Specify the method you want to invoke at run-time, for example, as input from an application user.

The only way to invoke a method whose name is longer than namelengthmax characters is to use javaMethod. The Java and MATLAB calling syntax does not accept method names of this length.

With javaMethod, you can also specify the method to be invoked at run-time. In this situation, your code calls javaMethod with a string variable in place of the method_name argument. When you use javaMethod to invoke a static method, you can also use a string variable in place of the class name argument.

Note    Typically, you will not need to use javaMethod. The default MATLAB syntax for invoking a Java method is somewhat simpler and is preferable for most applications. Use javaMethod primarily for the two cases described above.

Determining the Class of an Object

Invoking Static Methods on Java Classes