迭代器模式

迭代器UML.png

public  interface Iterator<T>{
    boolean hasNext();
    T next();
}

迭代器接口

public class ConcreteIterator<T> implements Iterator<T> {
    private List<T> list = new ArrayList<T>();
    private int cursor = 0;
    
    public ConcreteIterator(List<T> list){
        this.list = list;
    }
    
    public boolean hasNext(){
        return cursor != list.size();
    }
    
    public T next(){
        T obj = null;
        if(this.next()){
            obj = this.list.get(cursor++);
        }
        return obj;
    }
}

具体迭代器类

public interface Aggregate<T>{
    void add(T obj);
    void remove(T obj);
    Iterator<T> iterator();
}

容器接口

public class    ConcreteAggregate<T> implements Aggregate<T>{
    private List<T> list = new ArrayList<>();
    public void add(T obj){
        list.add(obj);
    }
    public void remove(T obj){
        list.remove(obj);
    }
    public Iterator<T> iterator(){
        return new ConcreteIterator<T>(list);
    }
}

具体容器类

public class Client{
    public static void main(String args[]){
        Aggregate<String> data = new ConcreteAggregate<>();
        data.add("1");
        data.add("2");
        data.add("3");
        data.add("4");
        Iterator<String> i = data.iterator();
        whihe(i.hasNext()){
            System.out.print(i.next());
        }
    }
}

客户端

个人理解

在java中的集合是迭代器模式的最好体现。在Android中数据库查询所用到的Cursor，用query方法查询数据库会返回一个Cursor游标，用它来遍历数据。