Map集合的两种遍历方式

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

public class MapTest {
	
	public static void main(String[] args) {
		
		HashMap map = new HashMap();
		
		map.put("a", "张三");
		map.put("b", "李四");
		map.put("c", "王五");
		map.put("a", "赵六");
		map.put("d", null);

		System.out.println("---遍历方式一---");
		
		Set set = map.keySet();	//返回key的集合，key是不能重复的  对应于set集合内容是不能重复的！
		
		for(Iterator iter = set.iterator(); iter.hasNext();){
			
			String key = (String)iter.next();
			String value = (String)map.get(key);
			
			System.out.println(key + "----" + value);
		}
		
		
		System.out.println("---遍历方式二---");
		
		Set set2 = map.entrySet();
		
		for(Iterator iter = set2.iterator(); iter.hasNext();){
		
			Map.Entry entry = (Map.Entry)iter.next();
			
			String key = (String)entry.getKey();
			String value = (String)entry.getValue();
			
			System.out.println(key + "---" + value);
		}
		
	}
}