Friday, January 30, 2009

defining an interface  


An interface declaration consists of modifiers, the keyword interface, the interface name, a comma-separated list of parent interfaces (if any), and the interface body. For example: 
public interface GroupedInterface extends Interface1,
  Interface2, Interface3 {

  // constant declarations
  double E = 2.718282; // base of natural logarithms

  // method signatures
  void doSomething (int i, double x);
  int doSomethingElse(String s);

The public access specifier indicates that the interface can be used by any class in any package. If you do not specify that the interface is public, your interface will be accessible only to classes defined in the same package as the interface. 

An interface can extend other interfaces, just as a class can extend or subclass another class. However, whereas a class can extend only one other class, an interface can extend any number of interfaces. The interface declaration includes a comma-separated list of all the interfaces that it extends.

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