If statement in while loop doesn't work

Question

public static void main(String[] args) {
    int i = 0;
    while(i==0){
        System.out.println("Possibilities: R, T, O and X.\nYour choice: ");
        Scanner scan = new Scanner(System.in);
        String bla = scan.nextLine();
        System.out.println(bla);
        if(bla=="R"){
            System.out.println("S or B?\n Your choice: ");
            String derp = scan.nextLine();
            if(derp=="S"){
                String rekeningNummer = spaarRekening.getRekeningNummer();
                }
        }
        if(bla=="T"){
            System.out.println("dit is T");
        }
        if(bla=="O"){

        }
        if(bla=="X"){

        }
        else{
            System.out.println("Impossible. Try again.");
        }
    i+=1;
    }

}

I was trying to run this program, but when it comes across an if statement it ignores it. I don't know why and I am running out of ideas.

score 9 · Accepted Answer · edited May 23 '17 at 12:21

9

To compare String instance, use equals() since it is an Object

See

Java String.equals versus ==

edited May 23 '17 at 12:21

Community

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answered Jun 12 '12 at 11:30

jmj

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thanks i appreciate it, doesn't state it anywhere in the: _Introduction to Java programming_ – Rick Overkleeft Jun 12 '12 at 11:34
You are welcome, It must be mentioned somewhere in introduction books – jmj Jun 12 '12 at 11:35
Couldn't find it anywhere, but its not always easy to find things in a book with close to 1500 pages. – Rick Overkleeft Jun 12 '12 at 11:43
1

:) then may be change the book – jmj Jun 12 '12 at 11:45
check appendix for `equals()` it must be there – jmj Jun 12 '12 at 11:47

score 5 · Answer 2 · edited Jun 12 '12 at 12:59

5

Use .equals() .Don't use == because it compares Strings refrences and not Strings characters.

 if (bla.equals("T")) {
     System.out.println("dit is T");
 }
 if (bla.equals("O")) {

 }

edited Jun 12 '12 at 12:59

sloth

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answered Jun 12 '12 at 11:30

Samir Mangroliya

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thanks i appreciate it, doesn't state it anywhere in the: _Introduction to Java programming_ – Rick Overkleeft Jun 12 '12 at 11:34

score 4 · Answer 3 · answered Jun 12 '12 at 11:30

4

== is not a String comparison operator.

You should use .equals() to compare Strings.

answered Jun 12 '12 at 11:30

Autar

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thanks i appreciate it, doesn't state it anywhere in the: _Introduction to Java programming_ – Rick Overkleeft Jun 12 '12 at 11:34

Ahmad · Answer 4 · 2012-06-12T12:04:21.880

Let's assume we have two strings. String str1= "blah"; String str2= new String("blah");

There are two levels of equality chacking in Java.

You may want to test whether the two referance variable str1 and str2 points to the same String object. we usually do this check by str1==str2.
You may want to test whether Strings referenced by str1 and str2 are equal in their meaning. we usually do this by invoking equals method i.e. str1.equals(str2) or str2.equals(str1).

To be more clear, your statement "bla=="R"" checks whether referances returned by ""R"" and and bla point to the same object or not, which is not actually the thing you want. You want to check whether String referanced by bla is equal to "R" by meaning or not. So If you want to compare objects by meaning in java, you will have to call equals() method on that object.

score 0 · Answer 5 · answered Jun 12 '12 at 11:48

0

Don't use == use .equals() since it is an String Object

answered Jun 12 '12 at 11:48

chaitu

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If statement in while loop doesn't work

5 Answers5