Strings == operator compares refrences or not?

Question

public class Test
{
    public static void main(String args[])
    {
        String a="meow";
        String b=a+"deal";
        String c="meowdeal";
        System.out.println(b==c);
    }
}

According to me == operators compares refrences . So b==c should print "true" But it prints "false" . I checked by printing hashcode of "b"and "c" .

Hashcode of both are same

The hashcodes of strings are based on the _content_, like `equals`, not the _references_, like `==` . — khelwood, Mar 23 '17 at 11:03
*According to me == operators compares refrences* then why are you using it to compare values? — Tim, Mar 23 '17 at 11:03
*According to me == operators compare references* and it does. `b` and `c` refer to completely different objects. — D.Shawley, Mar 23 '17 at 11:04
You are correct that the `==` operators compares refrences. You are not setting `c` to refer to the same string object as `b`. So `b == c` should return false. Which it seems it does. — Ole V.V., Mar 23 '17 at 11:17

score 1 · Answer 1 · answered Mar 23 '17 at 11:01

1

== compares references, but the reference to b and c are different - they're two different String instances although the contain the same content.

If you want to compare the content of both Strings, use equals().

answered Mar 23 '17 at 11:01

Malt

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If refrences are different, how come hashcode of both are sa – user6664723 Mar 23 '17 at 11:07
1

Hashcode is calculated on the content of the strings. – Markus Benko Mar 23 '17 at 11:08
1

The `hashCode()` is based on the content of the Strings, not their reference. – Malt Mar 23 '17 at 11:09

Stephen C · Answer 2 · 2017-03-23T11:38:15.930

1

According to me == operators compares refrences .

That is correct. The == operator compares references if both operands are reference types. (It is not correct if either operand is a primitive type ... but that's a different topic.)

So b==c should print "true" But it prints "false" . I checked by printing hashcode of "b"and "c" .

Your reasoning is incorrect.

   String a = "meow";
   String b = a + "deal";
   String c = "meowdeal";

In fact, when that code has finished b and c refer to different string objects that have the same value. In fact, the JLS states that the + operator creates a new string objext ... unless the expression is a constant expression. (And it doesn't qualify as a constant expression in this case, because a is a variable.)

So b == c is false ... BECAUSE == is comparing references, and the references are different.

edited Mar 23 '17 at 11:38

answered Mar 23 '17 at 11:05

Stephen C

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If refrences are different how come hashcode of both are same? – user6664723 Mar 23 '17 at 11:08
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The hashcodes of strings are based on the string's value, NOT on its identity (reference). Read the javadoc for `String.hashCode()` – Stephen C Mar 23 '17 at 11:09
Hashcode is calculated on the content of the strings. – Markus Benko Mar 23 '17 at 11:09

score 0 · Answer 3 · answered Mar 23 '17 at 11:02

0

You should use b.equals(c) for objects and == for primitive types

answered Mar 23 '17 at 11:02

shmakova

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Strings == operator compares refrences or not?

3 Answers3