Interface

In the Abstraction/Interface section, we talked about an interface in general terms. In this section, we are going to describe a Java language construct that expresses it.

An interface presents what can be expected of an object. It hides the implementation and exposes only method signatures with return values. For example, here is an interface that declares two abstract methods:

interface SomeInterface {
    void method1();
    String method2(int i);
}

And here is a class that implements it:

class SomeClass implements SomeInterface{
    public void method1(){
        //method body
    }
    public String method2(int i) {
        //method body
        return "abc";
    }
}

An interface cannot be instantiated. An object of an interface type can be created only by creating an object of a class that implements this interface:

SomeInterface si = new SomeClass(); 

If not all...