Common Gotchas

 

In the same spirit of other platforms, it seemed logical to follow up with this question: What are common non-obvious mistakes in Java? Things that seem like they ought to work, but don't.

I won't give guidelines as to how to structure answers, or what's "too easy" to be considered a gotcha, since that's what the voting is for.

See also:

  • Perl - Common gotchas
  • .NET - Common gotchas

    • Comparing equality of objects using == instead of .equals() -- which behaves completely differently for primitives.

    This gotcha ensures newcomers are befuddled when "foo" == "foo" but new String("foo") != new String("foo") . 

    "a,b,c,d,,,".split(",").length

    returns 4, not 7 as you might (and I certainly did) expect. split ignores all trailing empty Strings returned. That means: 

    ",,,a,b,c,d".split(",").length

    returns 7! To get what I would think of as the "least astonishing" behaviour, you need to do something quite astonishing: 

    "a,b,c,d,,,".split(",",-1).length

    to get 7.

    Overriding equals() but not hashCode()

    It can have really unexpected results when using maps, sets or lists.

    链接地址: http://www.djcxy.com/p/17898.html

    上一篇: 用PHP替换JAVA以实现PKCS5加密

    下一篇: 共同的问题