D&A Aufgabensatz 4 - Dequeue

Dequeue.java

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * Primitive Dequeue-Klasse, die ohne Generics implementiert wurde.
 * 
 * @author Andy Villiger
 */
public class Dequeue {
    
    public class DequeueIterator implements Iterator {

        private Dequeue queue;
        private Element current;
        
        public DequeueIterator(Dequeue queue) {
            this.queue = queue;
            this.current = queue.front;
        }
        
        @Override
        public boolean hasNext() {
            return (current.next.value != null);
        }

        @Override
        public Object next() {
            current = current.next;
            if (current.value != null) {
                return current.value;
            }
            
            throw new NoSuchElementException();
        }

        @Override
        public void remove() {
            queue.remove(current.value);
        }
        
        public Element getCurrent() {
            return current;
        }
        
    }
    
    public class Element {
        public Element prev;
        public Element next;
        public Object value;
    }
    
    private Element front;
    private Element back;
    
    public Dequeue() {
        front = new Element();
        back = new Element();
        front.next = back;
        back.prev = front;
    }
    
    public void pushBack(Object object) {
        Element element = new Element();
        element.value = object;
        element.prev = back.prev;
        element.next = back;
        element.prev.next = element;
        back.prev = element;
    }
    
    public void pushFront(Object object) {
        Element element = new Element();
        element.value = object;
        element.next = front.next;
        element.prev = front;
        element.next.prev = element;
        front.next = element;
    }
    
    public Object popBack() {
        Object value = back.prev.value;
        if (value != null) {
            back.prev = back.prev.prev;
            back.prev.next = back;
        }
        
        return value;
    }
    
    public Object popFront() {
        Object value = front.next.value;
        if (value != null) {
            front.next = front.next.next;
            front.next.prev = front;
        }
        
        return value;
    }
    
    public Object back() {
        return back.prev.value;
    }
    
    public Object front() {
        return front.next.value;
    }
    
    public DequeueIterator iterator() {
        return new DequeueIterator(this);
    }
    
    public void remove(Object object) {
        DequeueIterator it = iterator();
        while(it.hasNext()) {
            Object current = it.next();
            if (current.equals(object)){
                Element prev = it.getCurrent().prev;
                Element next = it.getCurrent().next;
                prev.next = next;
                next.prev = prev;
                
                return;
            }
        }
    }
    
    @Override
    public String toString() {
        String result = new String();
        DequeueIterator it = iterator();
        while(it.hasNext()) {
            Object current = it.next();
            if (result.length() > 0) {
                result += ", ";
            }
            
            result += current;
        }
        
        return result;
    }
    
    public static void main(String[] args) {
        Dequeue queue = new Dequeue();
        queue.pushBack("Hello");
        queue.pushBack("World");
        queue.pushFront("Mega");
        System.out.println(queue);
        
        queue.remove("Mega");
        System.out.println(queue);
        
        queue.popBack();
        System.out.println(queue);
    }
}