See if file reads something in Java

Question

I created a document called doc.txt, and in it I wrote "blaha". I wrote a program to see if it says blaha.

    File file = new File("C:/Users/Public/doc.txt");
    if (file.exists()){
     FileReader fr = new FileReader(file);
     LineNumberReader ln = new LineNumberReader(fr);
        while (ln.getLineNumber() == 0){
          String s = ln.readLine();
          System.out.println(s);
          if(s=="blaha"){
              System.out.println("Match");
          }else{
              System.out.println("Nomatch");
          }
    }
    }

And when I run the program, it always says Nomatch. Why is this?

Compare `String` values with `String`'s `equals` method, not with the `==` operator. — rgettman, Nov 25 '13 at 20:57

Óscar López · Answer 1 · 2013-11-25T21:04:11.043

6

To compare strings for value equality (whether two objects have the same value) do this:

s.equals("blaha")

The == operator tests for reference identity (whether two objects are one and the same). Most of the time, you're interested in equality.

edited Nov 25 '13 at 21:04

answered Nov 25 '13 at 20:57

Óscar López

232,561
37
312
386

1

Also, for more jargon, `==` for reference equality, `.equals()` for value equality. – Sotirios Delimanolis Nov 25 '13 at 21:02

score 1 · Answer 2 · answered Nov 25 '13 at 20:58

1

Because blaha != trollface. Also, you're going to want to make that more robust to handle trailing white space. You probably want to use trim() on the string. Also, use String.equals() or string.contains().

answered Nov 25 '13 at 20:58

Dodd10x

3,344
1
18
27

Sorry, when I originally used trollface, but didn't want to post that on the internet. – user1797443 Nov 25 '13 at 21:00

score 0 · Answer 3 · answered Nov 25 '13 at 21:06

0

First of all always use .equals. No ifs and no buts. Read this for details: http://www.coderanch.com/how-to/java/AvoidTheEqualityOperator

answered Nov 25 '13 at 21:06

systemhalted

818
9
24

See if file reads something in Java

3 Answers3