点击这里成为作者 · 更新于 2017-08-20 12:00:07

Super 程序题

题目一

class Base{
    Base(){
        System.out.println("Base");
    }
}

public class Checket extends Base{
    Checket(){
        System.out.println("Checket");
        super();
    }
    public static void main(String argv[]){
        Checket a = new Checket();
    }
}

输出是什么? 是 compile time error. super() 必须放在前面.

放在前面之后,输出为 Base Checket

题目二

import java.util.Date;

public class Test extends Date{

    public static void main(String[] args) {
       new Test().test();
    }

    public void test(){
       System.out.println(super.getClass().getName());
    }
}

返回的结果是 Test

因为super.getClass().getName() 调用了父类的 getClass() 方法, 返回当前类

如果想得到父类的名称,应该用如下代码:

getClass().getSuperClass().getName()

题目三

public abstract class Car {

    String name = "Car";

    public String getName(){
        return name;
    }

    public abstract void demarre();
}

public class B extends Car{
    String name = "B";

    public String getName(){
        return name;
    }

    public void demarre() {
        System.out.println(getName() + " demarre");
    }
}

public class C extends B{
    String name = "C";

    public String getName(){
        return name;
    }

    public void demarreWithSuper() {
        System.out.println(super.getName() + " demarre");
    }

    public void demarreNoSuper() {
        System.out.println(getName() + " demarre");
    }
}

public class D extends B{
    public String getName(){
        return name;
    }

    public void demarreNoSuper() {
        System.out.println(getName() + " demarre");
    }
}

public class Test {
    public static void main(String[] args) {
        B b = new B();
        b.demarre();

        Car bCar = new B();
        bCar.demarre();

        C c = new C();
        c.demarre(); // c 里并没有定义这个函数
        c.demarreWithSuper();
        c.demarreNoSuper();

        D d = new D();
        d.demarre();

        transfer(c);    // TransferC
        transfer((B)c); // TransferB
        transfer(d);    // TransferB
    }

        public static void transfer(B b){
            System.out.println("TransferB");
            b.demarre();
        }

        public static void transfer(C c){
            System.out.println("TransferC");
            c.demarre();
        }
    }
}

输出是 B demarre B demarre C demarre B demarre C demarre B demarre TransferC C demarre TransferB C demarre TransferB B demarre

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