PK Cycle class

Cycle.java

public class Cycle
{
	private int elem;
	private Cycle next;

	public Cycle(int value, Cycle cycle) {
		elem = value;
		if (cycle == null) {
			next = this;
		} else {
			next = cycle.next;
			cycle.next = this;
		}
	}

	// Hilfsmethode
	public void add(int i) {
		Cycle walk = this.next;
		while (walk.next != this) {
			walk = walk.next;
		}

		walk.next = new Cycle(i, walk);
	}

	// Aufgabe 2
	@Override
	public String toString() {
		String ret = "[" + elem;
		Cycle walk = this.next;
		while (walk != this) {
			ret += ", " + walk.elem;
			walk = walk.next;
		}
		return ret + "]";
	}

	// Aufgabe 3
	@Override
	public boolean equals(Object o) {
		if (o == null)
			return false;
		else if (!this.getClass().equals(o.getClass()))
			return false;

		Cycle other = (Cycle)o;
		if (this.elem != other.elem) {
			return false;
		}

		Cycle walkMe = this.next;
		Cycle walkOther = other.next;

		while (walkMe != this) {
			if (walkMe.elem != walkOther.elem) {
				return false;
			}
			walkMe = walkMe.next;
			walkOther = walkOther.next;
		}

		// Bin ich auch beim anderen Zyklus wieder am Anfang?
		return (walkOther == other);
	}

	// Aufgabe 4
	public int getFirst() {
		return this.elem;
	}

	public int getIndex(int n) {
		if (n == 0) {
			// das bin ich!
			return this.elem;
		} else {
			return next.getIndex(n - 1);
		}
	}

	public int getLast() {
		Cycle walk = this.next;
		while (walk.next != this) {
			walk = walk.next;
		}
		return walk.elem;
	}

	// Aufgabe 5
	public int fold() {
		int sum = this.elem;
		Cycle walk = this.next;
		while (walk != this) {
			sum += walk.elem;
			walk = walk.next;
		}
		return sum;
	}

	// Aufgabe 6
	public Cycle map() {
		Cycle ret = new Cycle(this.elem % 5, null);
		Cycle walk = this.next;
		while (walk != this) {
			ret.add(walk.elem % 5);
			walk = walk.next;
		}
		return ret;
	}

	// Aufgabe 7
	public Cycle reduce() {
		if (this.elem < 0) {
			// Ich selbst bin negativ; mit dem nächsten Element weitermachen.
			// (Vorsicht: Endlosrekursion wenn alle Elemente negativ sind.)
			return next.reduce();
		}
		Cycle ret = new Cycle(this.elem, null);
		Cycle walk = this.next;
		while (walk != this) {
			if (walk.elem >= 0)
				ret.add(walk.elem);
			walk = walk.next;
		}
		return ret;
	}

	// Aufgabe 8
	public static void main(String[] args) {
		Cycle one = new Cycle(13, null);
		one.add(99);
		one.add(-12);
		one.add(-18);
		one.add(2);

		Cycle two = new Cycle(13, null);
		two.add(99);
		two.add(-66);
		two.add(-18);
		two.add(2);

		System.out.println(one.equals(two));
		// false

		Cycle m1 = one.map();
		Cycle m2 = two.map();
		System.out.println(m1.equals(m2));
		// false

		Cycle mr1 = m1.reduce();
		Cycle mr2 = m2.reduce();
		System.out.println(mr1.equals(mr2));
		// true

		int mrf1 = mr1.fold();
		int mrf2 = mr2.fold();
		System.out.println(mrf1 == mrf2);
		// true

		//zusatztests();
	}

	private static void zusatztests() {
		// ggf. aus der main-Methode aufrufen

		Cycle one = new Cycle(1, null);
		System.out.println(one);
		// [1]

		Cycle eqOne = new Cycle(10, null);
		eqOne.add(15);
		Cycle eqTwo = new Cycle(10, null);
		eqTwo.add(15);
		System.out.println(eqOne.equals(eqTwo));
		// true

		Cycle eq3 = new Cycle(10, null);
		eq3.add(15);
		eq3.add(10);
		System.out.println(eqOne.equals(eq3));
		// false

		System.out.println(eqOne.getFirst());
		// 10

		System.out.println(eqOne.getIndex(0));
		// 10

		System.out.println(eqOne.getIndex(1));
		// 15

		System.out.println(eqOne.getIndex(2));
		// 10

		System.out.println(eqOne.getIndex(3));
		// 15

		System.out.println(eqOne.getLast());
		// 15

		System.out.println(eqOne.fold());
		// 25

		Cycle testMap = new Cycle(3, null);
		testMap.add(14);
		System.out.println(testMap.map());
		// [3, 4]
		System.out.println(testMap);
		// [3, 14]

		System.out.println(eqOne.reduce());
		// [10, 15]
		System.out.println(eqOne);
		// [10, 15]

		Cycle negatives = new Cycle(-5, null);
		negatives.add(-10);
		negatives.add(13);
		negatives.add(-18);
		System.out.println(negatives.reduce());
		// [13]
		System.out.println(negatives);
		// [-5, -10, 13, -18]
	}
}