Sep. 5, 2006

What is the best way to check if a Java String object is empty?

Solution 1:

someString.equals("");

• Pros:
  • readable
• Cons:
  • possible null pointer exception if someString is null
  • create extra String object (""). Overhead can be reduced by using static final String EMPTY_STRING = "";
  • not very efficient because equals first does a string length comparison

Solution 2:

public boolean isNotNullAndEmpty(String str) {

	if((null != str) && (str.length() == 0)) {
		return true;
	}
	else {
		return false;
	}
	
	// ... or just
	// return (str == null) ? false : str.length() == 0;
}

• Pros:
  • tests for null string
  • efficient
  • abstraction
• Cons:
  • a bit more code to write

Solution 3:

"".equals(someString);

• Pros:
  • avoids the null pointer exception issue that Solution 1 has
  • readable but awkward at first. Maybe use EMPTY_STRING.equals(someString)
• Cons:
  • create extra String object (""). Overhead can be reduced by using static final String EMPTY_STRING = "";
  • not very efficient because equals first does a string length comparison

Conclusion

• Either use Solution 2 or Solution 3. If you use Solution 3, make sure that you use a static final empty string.