Defining an Interface

A interface is defined much like a class. This is the common form of an interface:

access interface name {

return-type method-name1(parameter);

return-type method-name2(parameter);

type final-varname1 = value;

type final-varname2 = value;

// ...

return-type method-nameN(parameter);

type final-varnameN = value;

}

In the given program, access is either public or not used. Whenever no access specifier is involved, then default access results and the interface are just available to other members of the package in that it is declared. Whenever it is declared as public, the interface could be used through any other code. Where name is the name of the interface and could be any valid identifier. Remember that the function that are declared have nobodies. They end along with a semicolon after the parameter list. They are essentially abstract functions; there could be no default implementation of any method specified inside an interface. Every class which involves an interface must implement all of the methods.

A Variable can be declared within of interface declarations. That are implicitly final and static, meaning the implementing class cannot modify them. They must also be initialized along with a constant value. All functions and variables are implicitly public if the interface that itself is declared as public.

Here is an instance of an interface definition. That will declares an easy interface that holds one method called callback ( ) which takes a single integer parameter.

interface Callback {

void callback (int param );

}