public class A {
    public void m1() {
        System.out.println("A m1");
    }
}

public class B extends A {

public void m1() {
    System.out.println("B m1");
}

public void m2() {
    System.out.println("B m2");
}

public class Result {

public static void main(String[] args) {
    // TODO Auto-generated method stub
    /*A a = new A();
    a.m1();

    B b = new B();
    b.m1();
    b.m2();
    */
    A ab = new B();
    ab.m1();
}