Default value of Java String: null vs ""

Question

The default value of a Java String is 'null'. However, when I instantiate the string, it seems to be an empty string instead. Can somebody explain this please ?

class Stuff
{
    String a;
    String b = new String();
}

class Demo
{
    public static void main( String[] args )
    {
       Stuff s = new Stuff();
       System.out.println( s.a );
       System.out.println( s.b );

       if( s.b.equals( "" ) )
       {
            System.out.println( "true" );
       }
    }
}

I'm guessing String b = new String() is the same as String b = "". — Ben
– Ben, Commented May 18, 2015 at 3:39
@Ben: Not really. It does create a new instance (which assigning to "" will not) — Thilo
– Thilo, Commented May 18, 2015 at 3:41
Interesting, I just saw this too, learning something new everyday~ — Ben
– Ben, Commented May 18, 2015 at 3:44
in addition to the answers below, null is a language concept meaning "no reference to an object", so when a String, or any object for that matter, is constructed, it can't chose to be null, even if it wanted to be. Logically it can only be an empty string. An instance of a class might define some other way to say that's its empty or not defined, but it can't say "hey I'm actually null". Not at the object reference level. — slipperyseal
– slipperyseal, Commented May 18, 2015 at 4:46

Elliott Frisch · Accepted Answer · 2015-05-18 03:40:34Z

3

The String() constructor Javaodc says,

Initializes a newly created String object so that it represents an empty character sequence. Note that use of this constructor is unnecessary since Strings are immutable.

Which matches your observed behavior.

answered May 18, 2015 at 3:40

Elliott Frisch

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Forseth11 · Accepted Answer · 2015-05-18 03:44:24Z

2

In java a default string or a string set as null has no value. By setting a string with "" or with new String() it will create a new instance of the String class. A string which is initiated with "" or new String() is just a String ready to be used. I guess you can think of it as a cup. If something is null you have no cup, but if something, such as this string, is initiated as new String() or "" you now have an empty cup.

answered May 18, 2015 at 3:44

Forseth11

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2 Comments

Ben Over a year ago

I like the cup analogy ^

Ben Over a year ago

Though according to @Thilo's response on the original question and this thread, String b = "" doesn't necessarily create a new instance of the String object, it may refer to an existing item in the intern pool.

Community · Accepted Answer · 2020-06-20 09:12:55Z

0

Well, the string b is not null anymore because you created a String and assigned it to the variable.

If you use the default constructor of String, you will get an empty String:

public String()

Initializes a newly created String object so that it represents an empty character sequence. Note that use of this constructor is unnecessary since Strings are immutable.

http://docs.oracle.com/javase/6/docs/api/java/lang/String.html#String()

edited Jun 20, 2020 at 9:12

CommunityBot

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answered May 18, 2015 at 3:40

TimoStaudinger

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