23种设计模式之迭代器模式

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

package designMode.iterator;

interface Aggregate {
    
    Iterator createIterator();
}

package designMode.iterator;

interface Iterator {
    
    Object first();
    
    Object next();
    
    boolean isDone();
    
    Object currentItem();
}

package designMode.iterator;

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

class ConcreteAggregate implements Aggregate{
    
    private List<Object> items = new ArrayList<Object>();

    @Override
    public Iterator createIterator() {
        return new ConcreteIterator(this);
    }
    
    public int count(){
        return items.size();
    }
    
    public Object getCurrent(int index){
        return items.get(index);
    }
    public void setCurrent(int index,Object value){
        items.add(index, value);
    }
}

package designMode.iterator;

class ConcreteIterator implements Iterator{
    
    private ConcreteAggregate aggregate;
    private int current;
    
    public  ConcreteIterator(ConcreteAggregate aggregate) {
        this.aggregate = aggregate;
    }

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

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

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

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

}

package designMode.iterator;

class Test {
    public static void main(String[] args) {
        ConcreteAggregate a = new ConcreteAggregate();
        a.setCurrent(0, "张三");
        a.setCurrent(1, "李四");
        a.setCurrent(2, "王五");
        a.setCurrent(3, "马六");
        a.setCurrent(4, "田七");
        a.setCurrent(5, "茅八");
        Iterator iter = new ConcreteIterator(a);
        Object firstItem = iter.first();
        System.out.println("第一个是："+firstItem);
        while(!iter.isDone()){
            System.out.println(iter.currentItem()+"已通过！");
            iter.next();
        }
    }
}