java设计模式之迭代器模式

 

一、定义

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。

二、代码实例

1. 需求

   自己写一个iterator迭代器，遍历list。

2. 代码实现

迭代器接口：

public interface Iterator {
    public Object first();

    public Object next();

    public boolean isDone();

    public Object currentItem();
}

具体迭代类型接口：

public interface Aggregate {
    public Iterator createIterator();
}

迭代器实现类：

public class ConcreteIterator implements 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 result = null;
        current++;
        if (current < aggregate.count()) {
            result = aggregate.get(current);
        }
        return result;
    }

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

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

list迭代器实现类：

public class ConcreteAggregate implements Aggregate {

    private List