《大话设计模式》Java代码示例（十六）之迭代器模式

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。

package iterator;

/**
 * 迭代器模式(Iterator)
 * 抽象类
 */
public abstract class Iterator {

    public abstract Object first();
    public abstract Object next();
    public abstract boolean isDone();
    public abstract Object currentItem();

}

package iterator;

/**
 * 迭代器模式(Iterator)
 * 聚集抽象类
 */
public abstract class Aggregate {

    public abstract Iterator createIterator();

}

package iterator;

/**
 * 迭代器模式(Iterator)
 * 具体迭代器
 */
public class ConcreteIterator extends Iterator {

    private ConcreteAggregate aggregate;
    private int current = 0;

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

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

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

    @Override
    public boolean isDone() {
        return current >= aggregate.count() ? true : false;
    }

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

}

package iterator;

import java.util.ArrayList;
import java.util.List;

/**
 * 迭代器模式(Iterator)
 * 具体聚集类
 */
public class ConcreteAggregate extends Aggregate {

    private List<Object> items = new ArrayList<>();

    @Override
    public Iterator createIterator() {
        return new ConcreteIterator(this);
    }

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

    public Object get(int index) {
        return items.get(index);
    }

    public void set(int index, Object object) {
        items.add(index, object);
    }

}

package iterator;

/**
 * 迭代器模式(Iterator)
 * 客户端main方法
 */
public class Client {

    public static void main(String[] args) {
        ConcreteAggregate aggregate = new ConcreteAggregate();

        aggregate.set(0, "大鸟");
        aggregate.set(1, "小菜");
        aggregate.set(2, "行李");
        aggregate.set(3, "老外");
        aggregate.set(4, "公交内部员工");
        aggregate.set(5, "小偷");

        Iterator iterator = new ConcreteIterator(aggregate);
        Object item = iterator.first();
        while (!iterator.isDone()) {
            System.out.println(iterator.currentItem() + " 请买车票！");
            iterator.next();
        }
    }

}

《大话设计模式》Java代码示例（十六）之迭代器模式

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