자바 익명 내부 클래스

If the purpose of class is only to override method ex: purpose of creating B class to override fun1
in this case you don't need to create B class

class A{
    void fun1(){
        System.out.println("fun1 in A ");
    }
}
class B extends A{
    void fun1(){
        System.out.println("fun1 in B");
    }
}

public class Program1
{
    public static void main(String[] args) {
        // A a = new B();
        // a.fun1(); //fun1 in B

        A obj = new A(){
            void fun1() {
                System.out.println("Anonymous Overidden method ");
            }
            // can't create 
            // void fun2(){
            //     System.out.println("fun2 method ");
            // }
        };
        obj.fun1(); // Anonymous Overidden method 
    }    
}

interface I1{
    void fun1();
}

class Implementor implements I1{
    public void fun1(){
        System.out.println("Implementation of fun1");
    }
}

if role of implementor class is only to implement I1 interface , so you can create anonymous inner class , you don't need to create implementor class

public class Program2 {
    public static void main(String[] args) {
        // Implementor i1 = new Implementor();
        // i1.fun1(); //Implementation of fun1

        I1 i = new I1(){
            public void fun1(){
                System.out.println("Anonymous implementation");
            }
        };
        i.fun1(); // Anonymous implementation
    }
}