Java - null instanceof Object的计算结果为true和false

Question

当我编译并运行此代码时:

public class Testing {
    public static void main(String... args) {
        Object obj = null;
        if (obj instanceof Object) {
            System.out.println("returned true"); 
        } else {
            System.out.println("returned false"); 
        }
        System.out.println(" " + obj instanceof Object);
    }
}

我在命令行上看到了这个:

C:\Users\xxxxxx\Desktop>java Testing
returned false
true

不应该"null instanceof someType"总是返回false？

Answer 1

这个:

" " + obj instanceof Object

被评估为:

(" " + obj ) instanceof Object

并且" " + obj确实是一个非空字符串,它是一个实例Object.