Java - Common Gotchas [closed]

Question

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

Answer 1

"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.