简介：提供一种方法顺序访问一个聚合对象中各个元素, 而又不需暴露该对象的内部表示。

目的：

总结：使用Iterator避免二次迭代

 

组成：

1，举例

package com.design.q.iterator.standard;import java.util.Iterator;@SuppressWarnings("unchecked")public class ArrayList
     
       implements Iterable
      
       {        private E[] array = (E[]) new Object[10];  //集合    private static final int INCREMENT = 10;   //集合扩展大小    private int size = 0;                      //集合实时大小    /**     * 集合元素添加     * @param e     */    public void add(E e){        if(size < array.length){            array[size ++] = e;        }else{            //集合大小不足时进行扩容            E[] copy = (E[]) new Object[array.length + INCREMENT];            System.arraycopy(array, 0, copy, 0, size);            copy[size ++] = e;            array = copy;        }    }        /**     * 集合数组化     * @return     */    public Object[] toArray(){        Object[] copy = new Object[size];        System.arraycopy(array, 0, copy, 0, size);        return copy;    }        /**     * 返回集合大小     * @return     */    public int size(){        return size;    }    @Override    public Iterator
       
         iterator() {        return new Ite();    }            private class Ite implements Iterator
        
         {                int index = 0;        @Override        public boolean hasNext() {            return index != size();        }        @Override        public E next() {            return array[index ++];        }                public void remove(){                    }            }    }
        
       
      
     

LinkedList

package com.design.q.iterator.standard;import java.util.Iterator;public class LinkedList
     
       implements Iterable
      
       {    private Entry
       
         header = new Entry
        
         (null, null, null);    private int size;        public LinkedList() {        header.next = header.previous = header;    }    /**     * 集合新增元素     * @param e     */    public void add(E e){        Entry
         
           newEntry = new Entry
          
           (e, header, header.next); newEntry.previous.next = newEntry; newEntry.next.previous = newEntry; size ++; } /** * 集合数组化 * @return */ public Object[] toArray(){ Object[] result = new Object[size]; int i = size - 1; for(Entry
           
             e = header.next; e != header; e = e.next){ result[i --] = e.value; } return result; } /** * 返回集合大小 * @return */ public int size(){ return size; } private static class Entry
            
             { E value; Entry
             
               previous; Entry
              
                next; public Entry(E value, Entry
               
                 previous, Entry
                
                  next){ super(); this.value = value; this.previous = previous; this.next = next; } } @Override public Iterator
                 
                   iterator() { return new Ite(); } private class Ite implements Iterator
                  
                   { Entry
                   
                     index = header; @Override public boolean hasNext() { return index.previous != header; } @Override public E next() { E e = index.previous.value; index = index.previous; return e; } @Override public void remove() { // TODO Auto-generated method stub } }}
                   
                  
                 
                
               
              
             
            
           
          
         
        
       
      
     

HashSet

package com.design.q.iterator.standard;import java.util.HashMap;import java.util.Iterator;import java.util.Map;public class HashSet
     
       implements Iterable
      
       {    private static final Object NULL = new Object();    private Map
       
         map = new HashMap<>();    /**     * 集合元素新增     * @param e     */    public void add(E e){        map.put(e, NULL);    }        /**     * 集合数组化     * @return     */    public Object[] toArray(){        return map.keySet().toArray();    }        /**     * 集合大小     * @return     */    public int size(){        return map.size();    }    @Override    public Iterator
        
          iterator() {        return map.keySet().iterator();    }}
        
       
      
     

2，Main

package com.design.q.iterator.standard;import java.util.Iterator;/** * 17-迭代器模式 *  * 使用Iterator避免二次迭代 */public class MainTest {    public static void main(String[] args) {                /**         * ArrayList迭代         */        ArrayList
     
       arrayList = new ArrayList<>();        for(int i = 0; i < 10; i++){            arrayList.add(i);        }        System.out.println("ArrayList 大小=" + arrayList.size());        Iterator
      
        arrayListIterator = arrayList.iterator();        while(arrayListIterator.hasNext()){            System.out.print(arrayListIterator.next() + " ");        }//        for(Integer i : arrayList){//            System.out.print(i + " ");//        }                /**         * LinkedList迭代         */        LinkedList
       
         linkedList = new LinkedList<>();        for(int i = 0; i < 10; i ++){            linkedList.add(i);        }        System.out.println("\nLinkedList 大小=" + linkedList.size());        Iterator
        
          linkedListIterator = linkedList.iterator();        while(linkedListIterator.hasNext()){            System.out.print(linkedListIterator.next() + " ");        }//        for(Integer i : linkedList){//            System.out.print(i + " ");//        }                /**         * HashSet迭代         */        HashSet
         
           hashSet = new HashSet<>();        for(int i = 0; i < 10; i ++){            hashSet.add(i);        }        System.out.println("\nHashSet 大小=" + hashSet.size());        Iterator
          
            hashSetIterator = hashSet.iterator(); while(hashSetIterator.hasNext()){ System.out.print(hashSetIterator.next() + " "); }// for(Integer i : hashSet){// System.out.print(i + " ");// } }}
          
         
        
       
      
     

3，Result

ArrayList 大小=100 1 2 3 4 5 6 7 8 9 LinkedList 大小=100 1 2 3 4 5 6 7 8 9 HashSet 大小=100 1 2 3 4 5 6 7 8 9