Question

I’m very new to Java, so I’m sorry if this is a bit too stupid for you. So, I have a class called Construct that has an instance variable previousState. I have a setter in that class, with the signature setPreviousState.

Then, in an other class I set the previous State of a Construct object with this code :

    ArrayList<Construct> sequence = new ArrayList<Construct>();
    do {
        Construct minimum = priorityQueue.delMin();
        for (Construct neighbor : minimum.neighbors()) {
            neighbor.setPreviousState(minimum);
            priorityQueue.insert(neighbor);
        }
        System.out.println(minimum);
        if (minimum.isGoalState()) {

            // Construct sequence backwards and return it
            sequence.add(minimum);
            while(minimum.previousState() != null) {
                sequence.add(0, minimum.previousState());
            }
            return sequence;
        }
    } while (true);

But while(minimum.previousState() != null) is an infinite loop because previousState() always references the same object. Why?

Answer 1

You never change the value of minimum in this loop, and it seems that the value of minimum.previousState() is also constant for each object [no side affects to method previousState()], you might want to add minimum = minimum.previousState(); to your while loop:

while(minimum.previousState() != null) {
   sequence.add(0, minimum.previousState());
   minimum = minimum.previousState();
}