java - 字符串比较

Question

有人知道为什么 String.compareTo 没有被编程为对 null 参数表现得更友好吗？

在我看来，下一个序列应该返回“1”，或者至少 javadoc 对于 NPE 应该更加具体。在这种情况下，equals() 返回 false，我猜 equals 和 compareTo 应该是一致的。

例如

String nullString = null;
System.out.println ("test".equals(nullString));
System.out.println ("test".compareTo(nullString));

正在抛出 NPE:

false
Exception in thread "main" java.lang.NullPointerException
    at java.lang.String.compareTo(String.java:1177)

添加到它。如果您要在代码中进行此比较，您会验证空值吗？

Answer 1

因为它是documented behavior of compareTo() (强调):

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.

至于.equals()返回false而不是NPEing，同样，它在the documentation中:

For any non-null reference value x, x.equals(null) should return false.