Super 程序题

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

super 程序题

Super 程序题