Super 程序題

題目一

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();
    }
}

輸出是什么？ 是 compile time error. super() 必須放在前面.

放在前面之后,輸出為 Base Checket

題目二

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());
    }
}

返回的結(jié)果是 Test

因為super.getClass().getName() 調(diào)用了父類的 getClass() 方法, 返回當前類

如果想得到父類的名稱，應該用如下代碼：

getClass().getSuperClass().getName()

題目三

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 里并沒有定義這個函數(shù)
        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();
        }
    }
}

輸出是 B demarre B demarre C demarre B demarre C demarre B demarre TransferC C demarre TransferB C demarre TransferB B demarre