Java comparison with == of two strings is false? [duplicate]

Answer 1

The answer is very simple: when you compare strings through == operator, you actually compare if two different variables refer to a single String object. And they don't, the string in the array and newly created "231" are different String objects with the same contents.

The right thing to do is to use the folllowing expression: "231".equals(parts[0]) or "231".equalsIgnoreCase(parts[0]). This will give you what you need and return true if these String objects contain the same values.

Answer 2

I thought it might be helpful to express the answer in a test case:

public class String231Test extends TestCase {
    private String  a;
    private String  b;

    protected void setUp() throws Exception {
        a = "231";
        StringBuffer sb = new StringBuffer();
        sb.append("231");
        b = sb.toString();
    }

    public void testEquals() throws Exception {
        assertTrue(a.equals(b));
    }

    public void testIdentity() throws Exception {
        assertFalse(a == b);
    }
}

Answer 3

If the strings are not interned, then == checks reference identity. Use:

 "231".equals(parts[0]);

instead.

Answer 4

Use equals method: parts[0].equals("231"). == operator compares object references.

Answer 5

As many others have already explained, you try to compare with equality operator, but then it would relies on Object.equals() instead of String.equals().

So you can do the job by explicitly calling String.equals(), but instead of writing

parts[0].equals("blahblah")

I would prefer such :

"blahblah".equals(parts[0])

As it avoids testing potential nullity of parts[0] (but be careful that parts variable itself could be null...)

Another way is using String.intern() :

if (parts[0].intern() == "blahblah") ...

See http://java.sun.com/j2se/1.4.2/docs/api/java/lang/String.html#intern() for more info on that.

Answer 6

"==" compares object references, in your case "231" is a different object than parts[0].

You want to use String.equals.

parts[0].equals("231")