HashMap是无序的，TreeMap是有序的
HashMap添加和删除映射关系效率更高
代码片.

public class Demo3 {
	public static void main(String[] args) {
		Map<String, String> map=new HashMap<String, String>();
		 for (int i =10 ; i < 15; i++) {
		        map.put(i + "", i + "");
		    }
		    
		Set<String> set =map.keySet();
		Iterator<String> it=set.iterator();
		
		//关于Map的for 循环
		for (String key : map.keySet()) {
	        System.out.println(key);
	    }
		/*while(it.hasNext()){
			String str=it.next();
			System.out.println(str);
			//System.out.println(map.get(str));
		}*/
		/*map.remove("01");
		it=map.keySet().iterator();
		while(it.hasNext()){
			System.out.println(it.next());
		}*/
		System.out.println("------");
		TreeMap<String, String> tree = new TreeMap<String, String>();
		tree.putAll(map);
		it=tree.keySet().iterator();
		while(it.hasNext()){
			String str=it.next();
			System.out.println(str);
			//System.out.println(map.get(str));
			
	}
 
}
}