Stuck In Infinite While Loop (with switch statement)

Question

I haven't used Java in a while and am having a simple yet frustrating error. My code is something like this:

public static void main(String[] args) throws IOException{
    String input = "";
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    while(input != "Q"){
        input = in.readLine().toUpperCase();
        switch(input){
            default: break;
            case "A": //do stuff break;
            case "B": //do stuff break;
        }
    }
    System.out.println("Out of the loop!"); //never reaches this statement
}

I ran the eclipse debugger and it clearly shows the input variable being changed to "Q" when entered by the user, but the while loop keeps restarting.

Do you want to `break` out of the switch statement or do you want to jump to the end of the `while` loop? Because in the latter case, the `break` targets the `switch` and needs an explicit label to work correctly. — Clashsoft, Sep 27 '15 at 19:58

singhakash · Accepted Answer · 2015-09-27T19:59:40.507

3

Change while to

while(!input.equals("Q"))

compare string with equals() not with ==

In addition use a break; after each case otherwise you would have a fallthrough.

edited Sep 27 '15 at 19:59

answered Sep 27 '15 at 19:56

singhakash

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.equals()! of course. thank you so much, ive been doing a lot of python recently and it's messing me up lol – P. Jindra Sep 27 '15 at 19:57
1

If you know that question is duplicate you should vote it as such instead of answering it. We don't really need thousand-th answer about that subject. I know that new users may not know it but you already have 5k, so use your *closing/flagging* privilege. – Pshemo Sep 27 '15 at 20:04
1

@Pshemo I keep that in mind next time – singhakash Sep 27 '15 at 20:10

score 0 · Answer 2 · answered Sep 27 '15 at 19:57

You should compare the strings using equals (values comparison) instead of == (which compares references):

while (!"Q".equals(input))

Hint: if you call equals on the string literal, it will not fail with NullPointerException in case input is, by some chance, null - in such case it would just return false

score 0 · Answer 3 · edited Sep 27 '15 at 20:17

0

You have to use input.equals("Q") when comparing strings.

edited Sep 27 '15 at 20:17

mmking

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answered Sep 27 '15 at 19:57

Joel Min

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Stuck In Infinite While Loop (with switch statement)

3 Answers3