Question 5-3

Define a class NumberIterator for iterating through a sequence of numbers. It should support the following methods.

NumberIterator(int start, int stop)

(Constructor method) Constructs an object for iterating through the integers beginning at start and going up to stop. The constructor assumes that start is less than stop.

boolean hasMoreNumbers()

Returns true if there are more numbers remaining in the sequence.

int nextNumber()

Returns the current number in the sequence and steps the iterator forward, so that the next call to this method returns the following number in the sequence. This method initiates a NoSuchElementException if the sequence has no more elements remaining.

public class NumberIteratorTest {
    public static void run() {
        NumberIterator it = new NumberIterator(5, 8);
        IO.print(it.nextNumber());
        while(it.hasMoreNumbers()) {
            int i = it.nextNumber();
            IO.print(" " + i);
        }
    }
}

Solution

public class NumberIterator {
    private int current;
    private int last;

    public NumberIterator(int start, int stop) {
        current = start;
        last = stop;
    }

    public boolean hasMoreNumbers() {
        return current <= last;
    }

    public int nextNumber() throws NoSuchElementException {
        if(current <= last) {
            current++;
            return current - 1;
        } else {
            throw new NoSuchElementException();
        }
    }
}