A very simple example to show the concept of interface in java

interface Test{
public void square(int j);
}

class Arithmetic implements Test{
public void square(int j){
int result;
result=(j*j);
System.out.println("Square Of The Integer Is="+result);
}
}

public class ToTestInt{
public static void main(String[] args){
Arithmetic ar=new Arithmetic();
ar.square(12);
}
}