设计模式之---迭代器模式

现在很多编程语言都通过发语法糖来支持这种模式了，比如Java的for-each，但我们对这个模式做个了解还是有必要的。

package iterator;

public interface Iterator {  
    public Object next();  
    public boolean hasNext();  
}  

package iterator;

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

public class ConcreteIterator implements Iterator {

	private List list = new ArrayList();
    private int cursor =0;  
    
    public ConcreteIterator(List list){  
        this.list = list;  
    }  
	@Override
	public Object next() {
		// TODO Auto-generated method stub
		Object obj = null;  
        if(this.hasNext()){  
            obj = this.list.get(cursor++);
        }  
        return obj;
	}

	@Override
	public boolean hasNext() {
		// TODO Auto-generated method stub
		return list.size()==cursor?false:true;
	}

}

package iterator;

public interface Aggregate {
	public void add(Object obj);  
    public void remove(Object obj);  
    public Iterator iterator();
}

package iterator;

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

public class ConcreteAggregate implements Aggregate {

	private List list = new ArrayList();
	@Override
	public void add(Object obj) {
		// TODO Auto-generated method stub
		list.add(obj);
	}

	@Override
	public void remove(Object obj) {
		// TODO Auto-generated method stub
		list.remove(obj);
	}

	@Override
	public Iterator iterator() {
		// TODO Auto-generated method stub
		return new ConcreteIterator(list);
	}

}

package iterator;

public class Client {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Aggregate ag = new ConcreteAggregate();  
        ag.add("小明");  
        ag.add("小红");  
        ag.add("小刚");  
        Iterator it = ag.iterator();  
        while(it.hasNext()){  
            String str = (String)it.next();  
            System.out.println(str);  
        } 
	}

}

迭代器模式 的优缺点：