史上最完整的集合类总结及hashMap遍历

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());
}
}

}