java – 当方法之间的差异是参数子类型时,将null传递给重写方法

参见英文答案 > Which overload will get selected for null in Java?3个
> Strange Java null behavior in Method Overloading 4个
OUTPUT：乙

为什么虚拟机调用此方法f(null){System.out.println(“B”);}？

为什么不f(null){System.out.println(“A”);}

public class Test{

    public static class A {}
    public static class B extends A {}

    public void f(A a) {System.out.println("A");}
    public void f(B a) {System.out.println("B");}

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

解决方法

If more than one member method is both accessible and applicable to a method invocation,it is necessary to choose one to provide the descriptor for the run-time method dispatch. The Java programming language uses the rule that the most specific method is chosen.

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