Adding and Removing Methods

Every method you add to the COBOL class must have a corresponding function in the Java wrapper class.

The Java function must do the following:

1. Declare the exceptions which can be thrown from an invoke of a COBOL method.

   By default, these are Exception (thrown if you raise an exception in COBOL) and CobolException (thrown by the COBOL run-time system). If your class is to be deployed either as an Enterprise JavaBean, or using Java Remote Method Invocation (RMI), you should also add RemoteException.

2. Construct a Java array containing the parameters to be passed from Java to the COBOL method.

   Parameters are passed from Java to the COBOL run-time system in a Java array.

3. Invoke one of the cobinvoke_ or cobinvokestatic_ methods provided by the class RuntimeSystem.java.

   There is a cobinvoke_ and cobinvokestatic_ method corresponding to each possible return type from a Java function (for example, cobinvoke_int returns an int). Use the cobinvoke_ methods for invoking OO COBOL instances. Use the cobinvokestatic_ methods for invoking OO COBOL classes.

   For the full list of cobinvoke_ functions, see the Java Run-time Class Library Reference, which is in help\mfcobol.docs.zip (Windows) or docs/mfcobol.docs.zip (UNIX) in your COBOL development system installation.

   You need to determine which Java data type maps to the return type from the COBOL method, and then choose the appropriate cobinvoke_ function. See the chapter Java Data Types for more information.

OO COBOL factory methods are mapped onto static functions in the Java wrapper.

The two code samples below show a COBOL instance method, and the corresponding function in the Java wrapper. This is the COBOL method.

 method-id. "myMethod".
 local-storage section.
*>---USER-CODE. Add any local storage items needed below.
 linkage Section.
 01 myParameter            pic x(4) comp-5.
 01 myReturnValue          pic x(4) comp-5.
 procedure division using by reference myParameter
                    returning myReturnValue.
*>---USER-CODE. Add method implementation below.
     exit method. 
end method "myMethod".

This is the Java wrapper method.

public int myMethod (Integer myParameter) throws Exception, 
                          CobolException, RemoteException 
{
    // Parameters are passed to COBOL in an array
    Object[] params = {myParameter};
    return ((int) cobinvoke_int ("myMethod", params)); }

Although the name of a method is usually the same for the Java wrapper class and the COBOL class, it does not have to be. This enables you to implement method overloading in the Java wrapper.

Method overloading enables you to have several methods with the same name, but which take different types or numbers of parameters. Java supports method overloading, but COBOL does not. But you can add overloaded functions to the Java wrapper, and have them call differently named methods in the COBOL class.

For example, you could have these overloaded functions in your Java wrapper class:

public int add (int a, int b) 
{...}
public int add (int a, int b, int c)
{...}

And map them to methods "add2" and "add3" in your COBOL class.