Java继承基类使用派生类方法

Question

最近我偶然发现了 Java 测试并发现了一个奇怪的行为。

class MainOne {
    
    private int i = 5;
    
    public MainOne() {
        System.out.println("MainOne says that I is " + getI());
    }
    
    public int getI() {
        System.out.println("MainOne getI was used");
        return i;
    }
    
}

public class TheTest extends MainOne {

    private static int i = 10;
    
    public TheTest() {
        System.out.println("TheTest says that I is " + super.getI());
    }
    
    
    public int getI() {
        System.out.println("TheTest getI was used");
        return i;
    }
    
    public static void main(String[] args) {
        TheTest test = new TheTest();
    }
    
}

结果是:

TheTest getI was used

MainOne says that I is 10.

MainOne getI was used

TheTest says that I is 5

问题是，发生了什么？基类怎么用它的后代方法？

Answer 1

这都是关于执行顺序和构造函数继承的。 TheTest 构造函数隐式调用 super MainOne 构造函数。

所以

public TheTest() {
    System.out.println("TheTest says that I is " + super.getI());
}

通话

public MainOne() {
    System.out.println("MainOne says that I is " + getI());
}

由于多态性，它调用覆盖的 getI()。

public int getI() {
    System.out.println("TheTest getI was used");
    return i;
}

这里的i就是TheTest中声明的static i。最后

super.getI());

被调用，它使用 MainOne 的 i。

你因此得到

TheTest getI was used

MainOne says that I is 10.

MainOne getI was used

TheTest says that I is 5

请注意，多态性不适用于字段，并且字段(无论是 static 还是 instance)可能会隐藏父类中的同名字段。