Why this java code gives different answers?

Question

Why the following java code gives answer as:

not equal
equal.

Code:

    String a=new String("abc");
    String b=new String("abc");
    String c="abc";
    String d="abc";


    if(a==b){
        System.out.println("equal");
    }else{
        System.out.println("not equal");
    }

    if(c==d){
        System.out.println("equal");
    }else{
        System.out.println("not equal");
    }

I am confused as to what is the way the two statements

        String a=new String("abc");
        String c="abc";

differ in ?
In simple words what is the difference between the two assignments ?
Any help will be appreciated.
Thanks

This has been asked **many** times before. Here is one explanation: http://stackoverflow.com/a/334613/367273 — NPE, Apr 12 '13 at 19:33
You should look at [String.intern()](http://docs.oracle.com/javase/6/docs/api/java/lang/String.html#intern%28%29) and research it carefully. `All literal strings and string-valued constant expressions are interned.` — OldCurmudgeon, Apr 12 '13 at 19:34

score 3 · Accepted Answer · answered Apr 12 '13 at 19:34

When you use a string literal to directly initialize a string variable, Java will intern the Java literal string, so that both string variables refer to the same actual string object.

When you use the new operator, you get a different object, even if the contents of the new string is the same as the string literal.

And as has been pointed out many times, the == operator compares object references to see if they point to the same object, and does not compare string contents.

score 2 · Answer 2 · answered Apr 12 '13 at 19:33

2

Don't use == to compare strings; use equals() method.

if(a.equals(b)) {
    System.out.println("equal");
}else{
    System.out.println("not equal");
}

answered Apr 12 '13 at 19:33

duffymo

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4

That doesn't answer why they are equal the second time. – 11684 Apr 12 '13 at 19:34
Yes, it does. They are the same reference, so == returns true. – duffymo Apr 12 '13 at 19:35
Does not really answer the question but is a good advice :) – atamanroman Apr 12 '13 at 19:37
It's not obvious that they are the same reference. Especially to a new programmer. – Shaded Apr 12 '13 at 19:37
It's obvious to anyone who's read how the equals method and the == operator work. And I'd argue that you shouldn't be programming or asking questions here if you haven't read the material. – duffymo Apr 12 '13 at 19:52

score 1 · Answer 3 · answered Apr 12 '13 at 19:34

1

Assigning a string literal will utilize the string pool (hence the equal reference), newing a String will always create a new instance which results in different objects.

answered Apr 12 '13 at 19:34

atamanroman

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Why this java code gives different answers?

3 Answers3