CODEWITHSUNDEEP
javaeclipse
Sacha
Sacha

Reputation: 111

Eclipse just runs forever in the middle of a program execution

I observe a really weird behavior. I'm pretty sure there's a bug in my code, but Eclipse's behavior is so strange that I cannot figure anything out.

First, here's my code: http://pastebin.com/JCaW53GM.

I'm trying to solve Project Euler's problem 96, i.e., I'm trying to build a Sudoku solver using Knuth's Dancing Links. After a lot of preparation, this procedure is supposed to solve the problem:

    private static void search(int k) {
            System.out.println("start search");
            if (masterHeader.right == masterHeader) {
                    return;
            }

            // choose column
            Column c = new Column("");
            int s = Integer.MAX_VALUE;
            for (Column j = (Column) masterHeader.right; j != masterHeader;
                            j = (Column) j.right) {
                    if (j.size < s) {
                            c = j;
                            s = j.size;
                    }
            }

            // dancing links
            c.cover();

            for (Datum r = c.bottom; r != c; r = r.bottom) {
                    o[k] = r;
                    for (Datum j = r.right; j != r; j = r.right) {
                            j.column.cover();
                    }
                    System.out.println("before calling search(" + k + " + 1)");
                    search(k + 1);
                    r = o[k];
                    c = r.column;
                    for (Datum j = r.left; j != r; j = j.left) {
                            j.uncover();
                    }
            }

            c.uncover();
    }

Whenever I run the program, I get the following output:

start search
before calling search(0 + 1)
start search
before calling search(1 + 1)
start search
before calling search(2 + 1)
start search
before calling search(3 + 1)
start search
before calling search(4 + 1)
start search
before calling search(5 + 1)
start search
before calling search(6 + 1)
start search
before calling search(7 + 1)
start search
before calling search(8 + 1)
start search

After that---nothing. There is no error, no overflow, Eclipse just continues running forever. I have no clue at all what this means. I'm pretty sure the fact that it stops at search(9) has something to do with the many nines in my code. But there is no error, and I'm at a loss.

Can anybody enlighten me? What does Eclipse want? What did I do wrong?

Edit: Gaaah! I completely overlooked that last "start search" of the output. That was what was confusing me. Guess I was just too tired... anyway, sorry to everyone for bothering you. Yes, it is clearly just a simple case of infinite loop. I hope I'll be able to debug that myself.

Upvotes: 1

Views: 357

Answers (1)

Makoto
Makoto

Reputation: 106508

r != c; is an expression that only makes sense if you're talking about the exact same instance of an object. Since both r and c are Datum objects, it will not evaluate to true unless they are the exact same instance.

What you probably want to do is define .equals instead on the Datum class. Then, you can call !r.equals(c) instead.

You could also do with a rename of those variables, as row and column are far more straightforward than r and c.

Upvotes: 2

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