Strings look the same but test says they are different

Question

I have some code which is effectively the following:

String a;
String b;
a = get_string_from_complex_procedure_1();
b = get_string_from_complex_procedure_2();
if (a != b)
{
    put_up_error_dialog("["+a+"] != ["+b+"]");
}

The code is designed such that a and b should end up identical, and indeed most of the time they are, but occasionally I get the error dialog appearing. The confusing thing though, is that the two strings appear identical to me when reported by the dialog. I'm wondering what sort of things can cause this problem?

Duplicate of *lots* of posts comparing strings using `==` or `!=`. Those only compare *references*. Use `equals` instead. — Jon Skeet, Sep 07 '12 at 09:50
possible duplicate of [How do I compare strings in Java?](http://stackoverflow.com/questions/513832/how-do-i-compare-strings-in-java) — MByD, Sep 07 '12 at 09:52
Sorry for the duplicate. I guess you will always get lots of duplicates for this question because it is not obvious what to search for. I was suspecting all sorts of subtle things like unicode vs ASCII characters or some such. — Mick, Sep 07 '12 at 10:12

score 5 · Accepted Answer · answered Sep 07 '12 at 09:52

5

Rewrite like this:

String a;
String b;
a = get_string_from_complex_procedure_1();
b = get_string_from_complex_procedure_2();
if (!a.equals(b))
{
    put_up_error_dialog("["+a+"] != ["+b+"]");
}

The == and != operators compare references, not values.

answered Sep 07 '12 at 09:52

Bart Friederichs

33,050
15
95
195

score 1 · Answer 2 · edited Sep 07 '12 at 09:53

1

You cannot use == and != on Strings. To compare two Strings use a.equals(b) and !a.equals(b)

edited Sep 07 '12 at 09:53

Baz

36,440
11
68
94

answered Sep 07 '12 at 09:52

slezadav

6,104
7
40
61

score 0 · Answer 3 · edited Sep 07 '12 at 09:54

0

Use of == or != in case of String compares reference (memory location) so better you use equals() method.

edited Sep 07 '12 at 09:54

Baz

36,440
11
68
94

answered Sep 07 '12 at 09:53

kanhai shah

1,193
10
14

score 0 · Answer 4 · answered Sep 07 '12 at 09:54

0

use

       a.equals(b); or  a.equalsIgnoreCase(b) to compare String.

answered Sep 07 '12 at 09:54

Rajendra

1,700
14
17

Strings look the same but test says they are different

4 Answers4