java的一些例题

第一题  属性与多态无关

package com.yan.test01;

public class Test01 {

        public static void main(String[] args) {

                A a = new B();

                System.out.println(a.num);

                System.out.println(((B)a).num);

                System.out.println(((A)((B)a)).num);

                System.out.println("-------------------");

                B b = new B();

                System.out.println(b.num);

                System.out.println(((A)b).num);

                System.out.println(((B)((A)b)).num);

        }

}

class A{

        int num = 1;

}

class B extends A{

        int num = 2;

}

第二题  实例初始化方法，属性与多态无关

package com.yan.test02;

public class Test02 {

        public static void main(String[] args) {

                Father f = new Son();

                System.out.println(f.x);

        }

}

class Father{

        int x = 10;

        public Father(){

                this.print();

                x = 20;

        }

        public void print(){

                System.out.println("Father.x = " + x);

        }

}

class Son extends Father{

        int x = 30;

        public Son(){

                this.print();

                x = 40;

        }

        public void print(){

                System.out.println("Son.x = " + x);

        }

}

第三题  多态，重写，实例初始化过程

package com.yan.test03;

public class Test03 {

        public static void main(String[] args) {

                Base b1 = new Base();

                Base b2 = new Sub();

        }

}

class Base {

        Base() {

                method(100);

        }

        public void method(int i) {

                System.out.println("base : " + i);

        }

}

class Sub extends Base {

        Sub() {

                super.method(70);

        }

        public void method(int j) {

                System.out.println("sub : " + j);

        }

}

第四题  多态、重载、重写

public class Test04 {

        public static void main(String[] args) {

                A a1 = new A();

                A a2 = new B();

                B b = new B();

                C c = new C();

                D d = new D();

                System.out.println("(1)" + a1.show(b));

                System.out.println("(2)" + a2.show(d));

                System.out.println("(3)" + b.show(c));

                System.out.println("(4)" + b.show(d));

        }

}

class A{

        public String show(D obj){

                return ("A and D");

        }

        public String show(A obj){

                return "A and A";

        }

}

class B extends A{

        public String show(B obj){

                return "B and B";

        }

        public String show(A obj){

                return "B and A";

        }

}

class C extends B{

}

class D extends B{

}

第五题  多态、重载、重写

public class Test05 {

        public static void main(String[] args) {

                A a1 = new A();

                A a2 = new B();

                B b = new B();

                C c = new C();

                D d = new D();

                System.out.println("(1)" + a1.show(b));

                System.out.println("(2)" + a2.show(d));

                System.out.println("(3)" + b.show(c));

                System.out.println("(4)" + b.show(d));

        }

}

class A {

        public String show(C obj) {

                return ("A and C");

        }

        public String show(A obj) {

                return "A and A";

        }

}

class B extends A {

        public String show(B obj) {

                return "B and B";

        }

        public String show(A obj) {

                return "B and A";

        }

}

class C extends B {

}

class D extends B {

}

第六题  属性与多态无关

public class Test06 {

        public static void main(String[] args) {

                Base b = new Sub();

                System.out.println(b.x);

        }

}

class Base{

        int x = 1;

}

class Sub extends Base{

        int x = 2;

}