Lesson 9	Method signatures and parameter modes
Objective	Describe Java mapping of type in method signature.

Method Signatures and Parameter Modes in Corba

As you have seen, the mapping of a parameter type is dependent on the IDL type of that parameter as well as the parameter passing mode of that parameter. To know what to expect from the IDL compiler, you should have a good handle on the possible combinations. View the table below to see an illustration of the mapping from IDL to Java for each primitive type and parameter passing mode. The columns for in and return are the same as are the columns for out and inout.

Java Mapping of Types in Method Signatures in CORBA IDL

The Java mapping of types in an IDL method signature depends on:

The IDL data type (e.g., short, long, string, etc.).
The parameter passing mode (in, out, inout).
The return type of the method.

The following table summarizes how IDL types are mapped to Java in different method signatures:

IDL Type	in Parameter Mapping	out Parameter Mapping	inout Parameter Mapping	Return Type Mapping
`short`	`short`	`ShortHolder`	`ShortHolder`	`short`
`long`	`int`	`IntHolder`	`IntHolder`	`int`
`long long`	`long`	`LongHolder`	`LongHolder`	`long`
`unsigned short`	`short`	`ShortHolder`	`ShortHolder`	`short`
`unsigned long`	`int`	`IntHolder`	`IntHolder`	`int`
`unsigned long long`	`long`	`LongHolder`	`LongHolder`	`long`
`float`	`float`	`FloatHolder`	`FloatHolder`	`float`
`double`	`double`	`DoubleHolder`	`DoubleHolder`	`double`
`char`	`char`	`CharHolder`	`CharHolder`	`char`
`wchar`	`char`	`CharHolder`	`CharHolder`	`char`
`string`	`java.lang.String`	`StringHolder`	`StringHolder`	`java.lang.String`
`wstring`	`java.lang.String`	`StringHolder`	`StringHolder`	`java.lang.String`
`boolean`	`boolean`	`BooleanHolder`	`BooleanHolder`	`boolean`
`octet`	`byte`	`ByteHolder`	`ByteHolder`	`byte`

Explanation

in parameters: Passed as primitive types or Java reference types directly.
out parameters: Mapped to CORBA-specific Holder classes (ShortHolder, IntHolder, etc.), allowing the method to return values via references.
inout parameters: Also use Holder classes, as they require both passing in and modifying values.
Return type: Corresponds directly to a Java primitive or object type.

Example CORBA IDL to Java Mapping
IDL Definition

interface ExampleInterface {
    short addShort(in short a, in short b);
    void getFloatValues(out float a, out float b);
    void updateString(inout string s);
};

Java Interface (Generated by IDL Compiler)

public interface ExampleInterface extends org.omg.CORBA.Object {
    public short addShort(short a, short b);  // 'in' params as primitive types, return type as short
    public void getFloatValues(FloatHolder a, FloatHolder b);  // 'out' params as FloatHolder
    public void updateString(StringHolder s);  // 'inout' param as StringHolder
}

This table serves as a useful guide for predicting how an IDL compiler translates IDL method signatures into Java method signatures in CORBA applications.

IDL	`in`	`out`	`Inout`	return
`short`	`short`	`ShortHolder`	`ShortHolder`	`short`
`long`	`int`	`IntHolder`	`IntHolder`	`int`
`long long`	`long`	`LongHolder`	`LongHolder`	`long`
`unsigned short`	`short`	`ShortHolder`	`ShortHolder`	`short`
`unsigned long`	`int`	`IntHolder`	`IntHolder`	`int`
`unsigned long long`	`long`	`LongHolder`	`LongHolder`	`long`
`float`	`float`	`FloatHolder`	`FloatHolder`	`float`
`double`	`double`	`DoubleHolder`	`DoubleHolder`	`double`
`char`	`char`	`CharHolder`	`CharHolder`	`char`
`wchar`	`char`	`CharHolder`	`CharHolder`	`char`
`string`	`java.lang.String`	`StringHolder`	`StringHolder`	`java.lang.String`
`wstring`	`java.lang.String`	`StringHolder`	`StringHolder`	`java.lang.String`
`boolean`	`boolean`	`BooleanHolder`	`BooleanHolder`	`boolean`
`octet`	`byte`	`ByteHolder`	`ByteHolder`	`byte`

In the next lesson, you will learn the mapping for attributes in IDL interfaces.