null value in java

Question

hello, i am getting an string from using swing and i need to validate if it is not null i use this code

if(site.equals(null)) {
    System.out.println("null");
} else  {
    System.out.println("notnull");
}

it always show "notnull" if there is null also

Answer 1

To test for actual nullity, use == like this:

if (site == null)

Or indeed the conditional operator, for situations like the one shown:

System.out.println(site == null ? "null" : "notnull");

Note that a null reference is not the same as an empty string. How do you want an empty string to behave? If you truly had a null reference, then your current code would have thrown a NullPointerException.

The simplest way for testing an empty string is with the isEmpty method:

System.out.println(site.isEmpty() ? "empty" : "not empty");

Note:

• This will throw an exception if site really is null
• This will treat whitespace as irrelevant

If you want to test for null/empty/empty-or-whitespace there are various third-party libraries which have that functionality.

Answer 2

Are you sure that the string is being assigned null the value, and not "null" the string?

Answer 3

The problem is probably related to the textbox you are using will always return a string, just an empty one.

Change your check to the following and see if it works.

if(site.equals(""))

Note that this won't stop them from simply putting a space in though. you would need to trim the input first.

Answer 4

The String.equals() method only returns true if the argument is not null, and then only if the argument is an identical String. See the documentation.

You should initially be using a direct comparison to find out if either string is null, before you do a further check for equivalence.

   if (site == null) ...

Answer 5

Have you tried stringutils class? Here is the link --> http://commons.apache.org/lang/api/org/apache/commons/lang/StringUtils.html

You can check for string "nullness" and "emptiness" in a null-safe way and act accordingly