史上最完整的集合类总结及hashMap遍历

一.java集合类的比较：

二、HashMap的遍历共有两种：

1.利用entrySet 键值对映射：

Map map = new HashMap();

Iterator it = map.entrySet().iterator();

while(it.hashNext()){

    Map.Entry s = (Map.Entry)it.next();

    System.out.println(s.getKey());

    System.out.println(s.getValue());

}

2.利用keySet：

Map map = new HashMap();

Iterator it = map.keySet().iterator();

while(it.hasNext()){

      Object key = it.next();

      System.out.println(key);

      System.out.println(map.get(key));

}

LinkedHashMap的遍历,保证读取数据的顺序和put的顺序一致：

/**
 * LinkedHashMap倒序
 * @author zzw
 *
 */
public class LinkedHashMapSort {
 
    public static void main(String[] args) {
        LinkedHashMap <String,String > linkedhashmap = new LinkedHashMap<String,String>();
        linkedhashmap.put("1","a");
        linkedhashmap.put("2","b");
        linkedhashmap.put("3","c");
        linkedhashmap.put("4","d");
        ListIterator<Map.Entry<String,String>> i=new ArrayList<Map.Entry<String,String>>
            (linkedhashmap.entrySet()).listIterator(linkedhashmap.size());
        while(i.hasPrevious()) {
            Map.Entry<String, String> entry=i.previous();
            System.out.println(entry.getKey()+":"+entry.getValue());
        }
    }
 
}