When “” == s is false but “”.equals( s ) is true

Question

EDIT Thanks for the prompt responses. Please see what the real question is. I have made it bold this time.

I do understand the difference between ==

Answer 1

If you use google code search, you can find lots of places where people make this same error: google for file:.java \=\=\ \"\" Of course, this can be a correct idiom in carefully controlled circumstances, but usually, its just a bug.

Answer 2

Check this reference: http://mindprod.com/jgloss/string.html#COMPARISON at the excellent Canadian Mind Products Java & Internet Glossary. Worth a bookmark.

Answer 3

Would you expect "abcde".substring(1,2) and "zbcdefgh".substring(1,2) to yield the same String object?

They both yield "equal" sub-strings extracted from two different Strings, but it seems quite reasonable that tehy are different objects, so == sees them as different.

Now consider when the substring has length 0, substring(1, 1). It yields a zero length String, but it's not surprising that the "abcde".substring(1,1) is a different object from "zbcdefgh".substring(1,2) and hence at least one of them is a different object from "".

Answer 4

You should try considering String.length() == 0.