Hi Friend,

The mechanism is Inheritance :

As the name suggests, inheritance means to take something that is already made. It is one of the most important feature of Object Oriented Programming. It is the concept that is used for reusability purpose. Inheritance is the mechanism through which we can derived classes from other classes. The derived class is called as child class or the subclass or we can say the extended class and the class from which we are deriving the subclass is called the base class or the parent class. To derive a class in java the keyword extends is used.

interface A {
void hello1();

}

interface A extends B {
void hello2();

}

For read more information on inheritence visit to :

http://www.roseindia.net/java/language/inheritance.shtml

Thanks