设计模式 - 行为型模式 - 迭代器模式

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//抽象聚合类
abstract class AbstractObjectList {
    protected List<Object> objects = new ArrayList<Object>();

    public AbstractObjectList(List objects) {
        this.objects = objects;
    }

    public void addObject(Object obj) {
        this.objects.add(obj);
    }

    public void removeObject(Object obj) {
        this.objects.remove(obj);
    }

    public List getObjects() {
        return this.objects;
    }

    //声明创建迭代器对象的抽象工厂方法
    public abstract AbstractIterator createIterator();
}

//商品数据类：具体聚合类
class ProductList extends AbstractObjectList {
    public ProductList(List products) {
        super(products);
    }

    //实现创建迭代器对象的具体工厂方法
    public AbstractIterator createIterator() {
        return new ProductIterator(this);
    }
}

//抽象迭代器
interface AbstractIterator {
    public void next(); //移至下一个元素
    public boolean isLast(); //判断是否为最后一个元素
    public void previous(); //移至上一个元素
    public boolean isFirst(); //判断是否为第一个元素
    public Object getNextItem(); //获取下一个元素
    public Object getPreviousItem(); //获取上一个元素
}

//商品迭代器：具体迭代器
class ProductIterator implements AbstractIterator {
    private ProductList productList;
    private List products;
    private int cursor1; //定义一个游标，用于记录正向遍历的位置
    private int cursor2; //定义一个游标，用于记录逆向遍历的位置

    public ProductIterator(ProductList list) {
        this.productList = list;
        this.products = list.getObjects(); //获取集合对象
        cursor1 = 0; //设置正向遍历游标的初始值
        cursor2 = products.size() - 1; //设置逆向遍历游标的初始值
    }

    public void next() {
        if (cursor1 < products.size()) {
            cursor1++;
        }
    }

    public boolean isLast() {
        return (cursor1 == products.size());
    }

    public void previous() {
        if (cursor2 > -1) {
            cursor2--;
        }
    }

    public boolean isFirst() {
        return (cursor2 == -1);
    }

    public Object getNextItem() {
        return products.get(cursor1);
    }

    public Object getPreviousItem() {
        return products.get(cursor2);
    }
}

class Client {
    public static void main(String args[]) {
        List products = new ArrayList();
        products.add("倚天剑");
        products.add("屠龙刀");
        products.add("断肠草");
        products.add("葵花宝典");
        products.add("四十二章经");
        AbstractObjectList list;
        AbstractIterator iterator;
        list = new ProductList(products); //创建聚合对象
        iterator = list.createIterator(); //创建迭代器对象
        System.out.println("正向遍历：");
        while (!iterator.isLast()) {
            System.out.print(iterator.getNextItem() + "，");
            iterator.next();
        }
        System.out.println();
        System.out.println("-----------------------------");
        System.out.println("逆向遍历：");
        while (!iterator.isFirst()) {
            System.out.print(iterator.getPreviousItem() + "，");
            iterator.previous();
        }
    }
}