Comparable 和 (MyClass)null

Question

说我有

public class MyClass 
     implements Comparable<MyClass>
{
    public int compareTo(MyClass mc)
    {
        //<implementation ommited>...
    }
}

Comparable 的文档说 "The natural ordering for a class C is said to be consistent with equals if and only if e1.compareTo(e2) == 0 has the same boolean value as e1.equals(e2) for every e1 and e2 of class C. Note that null is not an instance of any class, and e.compareTo(null) should throw a NullPointerException even though e.equals(null) returns false."

它说“e.compareTo(null) 应该抛出 NullPointerException”。

它是否也应该在执行 e.compareTo((MyClass)null) 时抛出 NullPointerException？

Answer 1

写e.compareTo(null)或e.compareTo((MyClass)null)有什么区别？

两个代码是一样的，如null is null. Even if you cast it to any type, it will be null only。

Answer 2

是的，它应该抛出 NullPointerException。

null 在运行时是 null，不管你在编译时给它什么类型。

您的代码无法判断您是调用了 e.compareTo((MyClass)null) 还是 e.compareTo(null)。一样的。

Comparable 和 (MyClass)null

Comparable and (MyClass)null

java

null

compare

nullpointerexception

comparable