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How to check if my string is equal to null?

Asked 2010-04-08T17:15:11.227
196

I want to perform some action ONLY IF my string has a meaningful value. So, I tried this.

if (!myString.equals("")) {
doSomething
}

and this

if (!myString.equals(null)) {
doSomething
}

and this

if ( (!myString.equals("")) && (!myString.equals(null))) {
doSomething
}

and this

if ( (!myString.equals("")) && (myString!=null)) {
doSomething
}

and this

if ( myString.length()>0) {
doSomething
}

And in all cases my program doSomething in spite on the fact that my string IS EMPTY. It equals to null. So, what is wrong with that?

ADDED:

I found the reason of the problem. The variable was declared as a string and, as a consequence, null assigned to this variable was transformed to "null"! So, if (!myString.equals("null")) works.

java string null equals conditional-operator
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2 Answers

7

You need to check that the myString object is null:

if (myString != null) {
    doSomething
}
answered 2010-04-08T17:17:08.643
3

This should work:

if (myString != null && !myString.equals(""))
    doSomething
}

If not, then myString likely has a value that you are not expecting. Try printing it out like this:

System.out.println("+" + myString + "+");

Using the '+' symbols to surround the string will show you if there is extra whitespace in there that you're not accounting for.

answered 2010-04-08T17:21:31.590

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