遍历
第一种:通过Map.keySet()遍历key和value
Map<String, Object> map = new HashMap<String, Object>();
map.put("aaa", 111);
map.put("bbb", 222);
map.put("ccc", 333);
map.put("ddd", 444);
System.out.println("第一种:通过Map.keySet()遍历key和value:");
//keySet获取map集合key的集合 然后在遍历key即可
for(String key:map.keySet()){
String value = map.get(key).toString();//
System.out.println("key:"+key+" vlaue:"+value);
}
第二种:通过Map.entrySet使用iterator遍历key和value
Iterator<Entry<String, Object>> it = map.entrySet().iterator();
while(it.hasNext()){
Entry<String, Object> entry = it.next();
System.out.println("key:"+entry.getKey()+" key:"+entry.getValue());
}
第三种:通过Map.entrySet遍历key和value ( 数据量大时推荐使用)
for (Map.Entry<String, Object> m : map.entrySet()) {
System.out.println("key:" + m.getKey() + " value:" + m.getValue());
}
第四种:通过Map.values()遍历所有的value,但不能遍历key
for(Object m:map.values()){
System.out.println(m);
}
排序
Map<String, String> tm=new TreeMap<String, String>();
tm.put("a", "ddd");
tm.put("b", "ccc");
tm.put("c", "bbb");
tm.put("d", "aaa");
//这里将map.entrySet()转换成list
List<Map.Entry<String,String>> list = new ArrayList<Map.Entry<String,String>>(tm.entrySet());
//然后通过比较器来实现排序
Collections.sort(list,new Comparator<Map.Entry<String,String>>() {
//降序排序
@Override
public int compare(Entry<String, String> o1,
Entry<String, String> o2) {
return o2.getValue().compareTo(o1.getValue());
}
});
for(Map.Entry<String,String> mapping:list){
System.out.println(mapping.getKey()+":"+mapping.getValue());
}