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
Java的for(Obj obj : Iterator)就是迭代器模式
//创建聚集类 保存列表 获取列表属性
public class ConcreteAggregate {
private List<Object> items = new ArrayList<Object>();
public int getCount() {
return items.size();
}
public Object getItem(int index) {
return items.get(index);
}
public void addItem(Object object) {
items.add(object);
}
}
//声明迭代器需要实现的接口
interface Iterator {
public Object first();
public Object next();
public boolean isDone();
public Object currentItem();
}
//具体的迭代类
public class ConcreteIterator implements Iterator {
private ConcreteAggregate aggregate;
private int current = 0;
//需要聚集类的引用,保存item到列表
public ConcreteIterator(ConcreteAggregate aggregate) {
this.aggregate = aggregate;
}
@Override
public Object first() {
return aggregate.getItem(0);
}
@Override
public Object next() {
Object obj = null;
current++;
if (current < aggregate.getCount()) {
obj = aggregate.getItem(current);
}
return obj;
}
@Override
public boolean isDone() {
return current >= aggregate.getCount() ? true : false;
}
@Override
public Object currentItem() {
return aggregate.getItem(current);
}
}
//客户代码
public static void main(String[] args) {
// TODO Auto-generated method stub
ConcreteAggregate a = new ConcreteAggregate();
a.addItem("Tom");
a.addItem("Jerry");
a.addItem("Jack");
a.addItem("Rose");
Iterator i = new ConcreteIterator(a);
Object item = i.first();
while(!i.isDone()) {
System.out.println("Hello " + i.currentItem());
i.next();
}
}
//输出
Hello Tom
Hello Jerry
Hello Jack
Hello Rose
迭代器分离了集合对象的遍历行为,抽象出一个迭代器负责。这既可以不暴露内部结构,也让外部代码透明地访问集合内部数据