Comparing two strings in Java

Question

Possible Duplicate:
Java String.equals versus ==

I know it' a dumb question but why this code doesn't work.

boolean correct = "SampleText"  == ((EditText)findViewById(R.id.editText1)).getText().toString();
    if(correct) ((TextView)findViewById(R.id.textView1)).setText("correct!");
    else ((TextView)findViewById(R.id.textView1)).setText("uncorrect!");

The point is to check if content of "editText1" is equal to "Sample Text"

you are actually do a identity check with two `String` instances. — Genzer, Jun 17 '12 at 16:29
use == for primitive data types only, use equals() method for objects and strings — David Kroukamp, Jun 17 '12 at 16:30
Look into [How do I compare strings in Java?](http://stackoverflow.com/questions/513832/how-do-i-compare-strings-in-java) — Luca Geretti, Jun 17 '12 at 16:32
@RicardoE http://developer.android.com/reference/android/widget/EditText.html — Dave Newton, Jun 17 '12 at 21:26
So what is the output of: System.out.println(R.id.editText1); ? — RicardoE, Jun 18 '12 at 22:47

score 26 · Accepted Answer · edited Sep 27 '18 at 13:50

26

In Java, two strings (and in general, two objects) must be compared using equals(), not ==. The == operator tests for identity (meaning: testing if two objects are exactly the same in memory), whereas the method equals() tests two objects for equality (meaning: testing if two objects have the same value), no matter if they're two different objects. Almost always you're interested in equality, not in identity.

To fix your code, do this:

String str = ((EditText)findViewById(R.id.editText1)).getText().toString();
boolean correct = "SampleText".equals(str);

Also notice that it's a good practice to put the string literal first in the call to equals(), in this way you're safe in case the second string is null, avoiding a possible NullPointerException.

edited Sep 27 '18 at 13:50

Taufiq Rahman

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answered Jun 17 '12 at 16:28

Óscar López

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*"Also notice that it's a good practice to put the string literal first in the call to `equals()`, in this way you're safe in case the second string is null, avoiding a possible `NullPointerException`."* In robust code, that's actually an argument **against** putting the literal first. You **want** the NPE if your logic fails to handle that situation prior to the comparison, most of the time, so you can fix the logic before release. – T.J. Crowder Jun 17 '12 at 16:39
@T.J.Crowder that's open to discussion. Some static-analysis checkers will generate a warning if you _don't_ compare strings as I suggested above. One could argue that comparing strings in this way handles a corner case better than explicitly testing at all places to see if a string is null – Óscar López Jun 17 '12 at 16:47
@T.J.Crowder for example, look at the `EqualsAvoidNull` check in [Checkstyle](http://checkstyle.sourceforge.net/config_coding.html) – Óscar López Jun 17 '12 at 16:50
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@ Óscar: As you say, it's something people can disagree on. I **never** check with the literal first, because it reads poorly (to native English speakers and indeed native speakers of most other western languages) and because, again, I want the NPE if I've done something stupid. So far? Precisely *zero* production bugs related to it. Some nice bugs caught in testing, which I then was able to fix. But again, it's something reasonable people can, and do, disagree on. :-) – T.J. Crowder Jun 17 '12 at 16:50

score 1 · Answer 2 · answered Jun 17 '12 at 16:31

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In Java Strings have to be compared with their equals() method:

String foo = "foo";
String bar = "bar";
if (foo.equals(bar)) System.out.println("correct");
else System.out.println("incorrect");

answered Jun 17 '12 at 16:31

nkr

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score 1 · Answer 3 · answered Jun 17 '12 at 16:37

to compare the values for two strings (for equality), you need to use equals, not == (or use equalsIgnoreCase if you do not care about case sensitivity).
Using equals will check the contents/values of the strings (as opposed to "==" which will only check if the two variables point to the same object - not the same value).

score 1 · Answer 4 · answered Jun 17 '12 at 17:28

The correct way to compare 2 objects in java is using equals() method of Object class And as String is an object in java, it should be compared in same way.

The correct way to compare a String is with,

s1.equals(s2)

So you can use this,

boolean correct = "SampleText".equals(((EditText)findViewById(R.id.editText1)).getText().toString());

score 0 · Answer 5 · answered Jun 17 '12 at 16:33

((TextView)findViewById(R.id.textView1)).setText("SampleTest".equals(((EditText)findViewById(R.id.editText1)).getText().toString()) ? "correct!" : "incorrect!");

It's a bit long and theres probably a better way you could do this. The .toString() feels weird!

Comparing two strings in Java

5 Answers5