CODEWITHSUNDEEP
java
shdw
shdw

Reputation: 87

Why is this while loop infinite?

int MATCH_LENGTH = 0;
int FINAL_MATCH_LENGTH = 0;
int FINAL_MATCH_POS = 0;

while (window.contains(next)) {
    int MATCH_POS = window.indexOf(next);
    boolean nextMatches = true;
    while (nextMatches = true) {
        int index = window.indexOf(next);
        index++;
        int positionOfNext = fileArray.indexOf(next);
        positionOfNext++;
        MATCH_LENGTH++;
        char afterNext = fileArray.get(positionOfNext);
        char afterNextInWindow = window.get(index);
        if (afterNext != afterNextInWindow) {
            nextMatches = false;
            if (MATCH_LENGTH > FINAL_MATCH_LENGTH) {
                FINAL_MATCH_POS = MATCH_POS;
                FINAL_MATCH_LENGTH = MATCH_LENGTH;
                MATCH_LENGTH = 0;
            }
            window.remove(window.indexOf(next));
        }
    }
}

I am running into an infinite loop here. I think it is because of the nextMatches boolean variable. However, I am not sure how that affects the program, as I have the condition for the while loop as while (window.contains(next)). However, I am removing the occurrences of next one by one, so eventually while (window.contains(next)) will have to return false and the while loop will have to break. My reasoning here might be flawed though with the remove line window.remove(window.indexOf(next));.

Or is some other part of my reasoning flawed?

Upvotes: 2

Views: 184

Answers (4)

Azodious
Azodious

Reputation: 13872

while (nextMatches == true) {

This condition will be false iff nextMatches is assigned with false.

The only place you are assigning it false, is in following code block:

if (afterNext != afterNextInWindow) {
    nextMatches = false;
    ...

Since, while is running infinite for you, it means nextMatches is never assigned with false when code executes, i.e if condition is always false.

This means, that in every iteration of while; afterNext is always equals to afterNextInWindow.

Upvotes: 2

daniel gratzer
daniel gratzer

Reputation: 53881

You made the classic = vs == mistake

while (nextMatches = true)

should be

while(nextMatches)

As a general rule, don't compare booleans to true and false. It just leads to these sort of weird bugs and makes the code less legible in my opinion. If you name your variables properly, Java conventions has booleans sound like a conditional. For example: isEmpty or isFull. This way things read like english: while(isFull)

I'm a bit confused on your logic, especially since int index = window.indexof(next) will not change anything. index will be redefined.

Upvotes: 7

shdw
shdw

Reputation: 87

I found the problem. It was this line: int index = window.indexOf(next);. I kept on redefining index as the same number over and over again, which caused the infinite loop. Problem solved!

Upvotes: 2

Subodh Ghulaxe
Subodh Ghulaxe

Reputation: 18651

The problem is here while (nextMatches = true) try put instead 

while (nextMatches == true)

Upvotes: 4

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