迭代器模式（Iterator）

迭代器模式（Iterator），提供一种方法顺序访问一个聚合对象中的各个元素，而又不暴露该对象的内部表示。

主方法

import java.util.ArrayList;
import java.util.List;
public class main {
    public static void main(String[] args) {
        ConcreteAggregate a = new ConcreteAggregate();
        List<Object> items = new ArrayList<Object>();
        items.add("大鸟");
        items.add("小菜");
        items.add("行李");
        items.add("老外");
        items.add("公交内部员工");
        items.add("小偷");
        a.setItems(items);

        Iterator i = new ConcreteIterator(a);
        while (!i.isDone()) {
            System.out.println(String.format("{%s}请买车票！", i.currentItem()));
            i.next();
        }
    }
}

抽象类

/**
 * 迭代器抽象类
 */
public abstract class Iterator {
    public abstract Object first();
    public abstract Object next();
    public abstract boolean isDone();
    public abstract Object currentItem();
}

/**
 * 聚集抽象类
 */
public abstract class Aggregate {
    public abstract Iterator createIterator();
}

实现类

public class ConcreteIterator extends Iterator {
    private ConcreteAggregate aggregate;
    private int current = 0;

    public ConcreteIterator(ConcreteAggregate aggregate) {
        this.aggregate = aggregate;
    }

    public Object first() {
        return aggregate.getItems().get(0);
    }

    public Object next() {
        Object ret = null;
        current++;
        if (current < aggregate.count()) {
            ret = aggregate.getItems().get(current);
        }
        return ret;
    }

    public boolean isDone() {
        return current >= aggregate.getItems().size() ? true : false;
    }

    public Object currentItem() {
        return aggregate.getItems().get(current);
    }
}

import java.util.ArrayList;
import java.util.List;
public class ConcreteAggregate extends Aggregate {
    private List<Object> items = new ArrayList<Object>();
    public Iterator createIterator() {
        return new ConcreteIterator(this);
    }

    public int count() {
        return items.size();
    }

    public List<Object> getItems() {
        return items;
    }

    public void setItems(List<Object> items) {
        this.items = items;
    }
}