Map集合相关

导入包
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Set;
1.循环打印键和值
        System.out.println("*****循环map集合,并打印键和值****");
        Map<Long, Object> map= new HashMap<Long, Object>();
        map.put(1L, 1);
        map.put(2L, "二");
        map.put(3L, new ArrayList<String>());
        for(Long key : map.keySet()){
        	System.out.println("key:"+key +" "+"value:"+map.get(key));
        } 
打印结果
*****循环map集合,并打印键和值****
key:1 value:1
key:2 value:二
key:3 value:[]


2.获取键的集合并转化成List(循环打印)
        
        System.out.println("*****获取map键并转化成list集合****");
        List<Long> keyList= new ArrayList<Long>(map.keySet());
        for(Long key : keyList) {
        	System.out.println("key:"+key);
        }

打印结果
*****获取map键并转化成list集合****
key:1
key:2
key:3
3.循环获取mapkey和value的类型
System.out.println("*****循环获取mapkey和value的类型****");
        Set keys  = map.keySet();
        Iterator it = keys.iterator();
        while (it.hasNext()){
	        Object key  = it.next();
	        Object value = map.get(key);
	        System.out.println("key类型:"+key.getClass().getName());
	        System.out.println("值类型:"+value.getClass().getName());
        }

打印结果
*****循环获取mapkey和value的类型****
key类型:java.lang.Long
值类型:java.lang.Integer
key类型:java.lang.Long
值类型:java.lang.String
key类型:java.lang.Long
值类型:java.util.ArrayList





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转载自blog.csdn.net/sunnyxie1/article/details/80912411