为什么我的 count 方法不应该返回 false ？

Question

I have coded a class where you have a start and an end as inputs, and where a counter counts either up or down depending on whether the start value is smaller or bigger than the end value. When the counter has reached the end value, it should return false, if not it should return true.

When I run this in a junit test my professor has made, it says "After reaching the end value, the count() method should return false". I don't understand what is wrong with code.

public class UpOrDownCounter {

    private int end;
    private int counter;
    private int start;
    private int increment;

    UpOrDownCounter(int start, int end){
        this.start = start;
        this.end = end;
        this.counter = start;

        isValid();

        if(start<end) {
            this.increment = 1;
        }
        else {
            this.increment = (-1);
        }
    }

    public void isValid() throws IllegalArgumentException{
        if(this.start == this.end) {
            throw new IllegalArgumentException("the start value can't be the same as the end value");
        }
    }

    public int getCounter() {
        return counter;
    }

    public boolean count() {
        counter += increment;
        if(this.counter == end) {
            this.counter == 0;
            return false;
        }
        else {
            return true;
        }
    }

    public String toString() {
        return "[counter = " + counter + "]";
    }

    public static void main(String [] args){
        UpOrDownCounter c = new UpOrDownCounter(3, 5);
        System.out.println(c.toString());
}

Answer 1

What happens to this.increment if start == end ? We need to call isValid(), so that the counter doesn't blow past either end of the range. Change your constructor to:

UpOrDownCounter(int start, int end) throws IllegalArgumentException {
    this.start = start;
    this.end = end;
    this.counter = start;

    isValid();

    if(start<end) {
        this.increment = 1;
    } else {
        this.increment = (-1);
    }
}