map集合转换

1.map转list:

List<String> mapKeyList = new ArrayList<String>(map.keySet());
List<String> mapValuesList = new ArrayList<String>(map.values());

2.map转set:

 Set<String> mapKeySet = map.keySet();
 Set<String> mapValuesSet = new HashSet<String>(map.values());

3.数组-set:

Set<String> set = new HashSet<String>(Arrays.asList(list))

反之:

 set.toArray(setList)

4.排序:

key排序:TreeMap treemap = new TreeMap(map); 升序

 Map<String, String> map = new TreeMap<String, String>(
                new Comparator<String>() {
                    public int compare(String obj1, String obj2) {
                        // 降序排序
                        return obj2.compareTo(obj1);
                    }
                });

value排序:

 //这里将map.entrySet()转换成list
        List<Map.Entry<String,String>> list = new ArrayList<Map.Entry<String,String>>(map.entrySet());
        //然后通过比较器来实现排序
        Collections.sort(list,new Comparator<Map.Entry<String,String>>() {
            //升序排序
            public int compare(Entry<String, String> o1,
                    Entry<String, String> o2) {
                return o1.getValue().compareTo(o2.getValue());
            }
            
        });

5.取值:

for(Map.Entry<String,String > entry:map.entrySet()){

System.out.println("key=" +entry.getKey() +" and value="+entry.getValue());

}

6.java8取值:

map.forEach((k,v)->System.out.println("key : " + k + "; value : " + v));

猜你喜欢