另一道关于继承的面试题

Question

题目描述

public class Base {

private String baseName = "base";

public Base() {
    callName();
}

public void callName() {
    System.out.println(baseName);
}

static class Sub extends Base {
    private String baseName = "sub";

    public void callName() {
        System.out.println(baseName);
    }
}

public static void main(String[] args) {
    Base b = new Sub();
}

}

你期待的结果是什么？实际看到的错误信息又是什么？

为什么会输出: null ????

Answer 1

public class Base {

private String baseName = "base";//1

public Base() {
    callName();//2
}

public void callName() {
    System.out.println(baseName);
}

static class Sub extends Base {
    private String baseName = "sub";

    public void callName() {
        System.out.println(baseName);//3
    }
}

public static void main(String[] args) {
    Base b = new Sub();
}
}

Base b = new Sub();先初始化父类，顺序如上面的1，2，3，进入callName方法时子类的属性还没有初始化执行代码，所以打印的是null.