With interfaces, type parameters can be used in method parameters, returns, and throws. The type parameters to be used are declared in the interface definition.

(a) Types of interfaces in which type parameters can be used

The following table describes the types of interfaces in which type parameters can be used for each Enterprise Bean type:

Table 4-5 Types of interfaces in which type parameters can be used

Legend:

Y: Can be used.

P: Can be used. However, a declared type parameter must be parameterized in the business interface. If the declared type parameter is not parameterized, either an error will occur or the operation will not be guaranteed.

N: Cannot be used.

--: Cannot be used (Java EE specifications).

(b) Precautions when a type parameter is used in a business interface

When a type parameter, defined in an interface, is parameterized in a business interface and the method of the parameterized business interface is redefined, an error might occur based on the combination of the location, wherein the type parameter is used, and the interface type. If an error occurs, take action by deleting the redefined method.

The following table describes the combinations that might result in an error, when a method is redefined in the business interface:

Table 4-6 Combination resulting in an error when a method is redefined in the business interface

Legend:

Y: The application is started successfully.

--: An error occurs when starting the application.

An error occurs when both the following conditions are applicable:

• The type parameter defined in the interface is parameterized.
• A method is redefined in the interface that inherits the interface in which the type parameter is parameterized.

The following is a coding example to show the occurrence of an error. In the following example, the definition of the method String get(Float args) must be deleted from the definition of MyInterface to recover from the error:

public interface SuperInterface<T> {
String get(T args);
}
 
// Redefine the method in which the parameterized SuperInterface is inherited.
public interface MyInterface
extends SuperInterface<Float> {
// To recover from the error, the following redefined method definition must be deleted.
    String get(Float args);
}
 

With classes, type parameters can be used within the method and the method signature.

The following table describes the types of classes in which type parameters can be used for each Enterprise Bean type:

Table 4-7 Types of classes in which type parameters can be used

Legend:

Y: Can be used.

--: Cannot be used (Application Server does not support this combination).

You cannot specify an annotation^# corresponding to Application Server in a generic method and a generic constructer. If you specify such an annotation, the annotation is ignored.

An example of a generic method and a generic constructor is given below.

# For details on annotations corresponding to Application Server, see 2.1 Supported range of corresponding applications in the uCosminexus Application Server API Reference Guide.

class MyClass{
 
// Generic constructor
<T1> MyClass(Collection<T1> c){};
 
// Generic method
<T2> void MyMethod(Collection<T2> c){};
 
}