https://sp18.datastructur.es/materials/discussion/disc04.pdf

    public class Animal{
        protected String name, noise;
        protected int age;
        public Animal(String name, int age){
            this.name = name;
            this.age = age;
            this.noise = "Huh?";
        }

        public String makeNoise(){
            if (age < 5) {
                return noise.toUpperCase();
            } else{
                return noise;
            }
        }

        public void greet(){
            System.out.println("Animal " + name + " says: " + makeNoise());
        }
    }
    public class Cat extends Animal{
        public Cat(String name){
            this.name = name;
            this.noise = "Meow!"
        }
        @Override
        public void greet(){
            System.out.println("Cat " + name + " says: " + makeNoise());
        }
    }
    /**
    (A) Animal Pluto says: Huh?
    (B) Cat Garfield says: Meow!
    (C) Dof Fido says: WOOF!
    (D) Cat Garfield says: Meow!
    (E) Cat Garfield says: Meow!
    //a是一个Animal类，而d是一个Dog，不是直接赋值，需要进行一个强制转换。
    */
     class A {
            public int x = 5;
            public void m1() {System.out.println("Am1-> " + x);}
            public void m2() {System.out.println("Am2-> " + this.x);}
            public void update() { x = 99;}
     }
     class B extends A {
            public void m2() {System.out.println("Bm2-> " + x);}
            public void m2(int y) {System.out.println("Bm2y-> " + y);}
            public void m3() {System.out.println("Bm3-> " + "called");}
     }
     class C extends B {
            public int y = x + 1;
            public void m2() {System.out.println("Cm2-> " + super.x);}
            public void m4() {System.out.println("Cm4-> " + super.super.x); }} //can't do super.super
            public void m5() {System.out.println("Cm5-> " + y);}
     }
     class D {
        public static void main (String[] args) {
            // B a0 = new A(); Dynamic type must be B or subclass of B
            // a0.m1(); cascading: prev line failed, so a0 can't be initialized
            // a0.m2(16); cascading: prev line failed, so a0 can't be initialized
            A b0 = new B();
            System.out.println(b0.x); [prints "5"]
            b0.m1(); //[prints "Am1-> 5"]
            b0.m2(); //[prints "Bm2-> 5"]
            // b0.m2(61); m2 (int y) not defined in static type of b0
            B b1 = new B();
            b1.m2(61); //[prints "Bm2y-> 61"]
            b1.m3(); //[prints "Bm3-> called"]
            A c0 = new C();
            c0.m2(); //[prints "cm2-> 5"]
            // C c1 = (A) new C(); Can't assign c1 to an A
            A a1 = (A) c0;
            C c2 = (C) a1;
            c2.m3(); [print Bm3-> called]
            // c2.m4(); C.m4() is invalid
            c2.m5(); //[print Cm5-> 6]
            ((C) c0).m3(); //[print Bm3-> called]
            Inheritance
            //(C) c0.m3(); NOT RUNTIME ERROR This would case the result of what the method returns and it returns void therefore compile-time error
            b0.update();
            b0.m1(); [print Am1-> 99]
        }
     }