Java String Comparison: style choice or optimization?

Question

I've been taking a look at some GWT code written by various people and there are different ways of comparing strings. I'm curious if this is just a style choice, or if one is more optimized than another:

"".equals(myString);

myString.equals("");

myString.isEmpty();

Is there a difference?

Answer 1

"".equals(myString);

will not throw a NullPointerException if myString is null. That is why a lot of developers use this form.

myString.isEmpty();

is the best way if myString is never null, because it explains what is going on. The compiler may optimize this or myString.equals(""), so it is more of a style choice. isEmpty() shows your intent better than equals(""), so it is generally preferred.

Answer 2

Both of the options using "" may require the creation of a temporary String object but the .isEmpty() function shouldn't.

If they bothered to put the .isEmpty() function in I say it is probably best to use it!

Answer 3

apache StringUtils provides some convenience methods for, well, String manipulation.

http://commons.apache.org/lang/api/org/apache/commons/lang/StringUtils.html#isBlank(java.lang.CharSequence)

check out that method and associated ones.

Answer 4

Beware that isEmpty() was added in Java 6, and, unfortunately, there are still people who complain pretty loudly if you don't support Java 1.4.

Answer 5

myString.isEmpty() is probably best if you are working on a recent version of Java (1.6). It is likely to perform better than myString.equals("") as it only needs to examine one string.

"".equals(myString) has the property of not throwing a null pointer exception if myString is null. However for that reason alone I'd avoid it as it is usually better to fail fast if you hit an unexpected condition. Otherwise some little bug in the future will be very difficult to track down.....

myString.equals("") is the most natural / idiomatic approach for people wanting to keep compatibility with older Java versions, or who just want to be very explicit about what they are comparing to.