简单介绍常用的三种Map：不足之处，欢迎指正！

HashMap：put数据是无序的；
TreeMap：key值按一定的顺序排序；数字做key，put数据是有序，非数字字符串做key，put数据无序；
LinkedHashMap：LinkedHashMap是有序的，且默认为插入顺序；

测试案例：

import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;public class day12 {public static void main(String[] args) {List<String> list1 = Arrays.asList("黄","河","之","水","天","上","来","奔","流","到","海","不","复","回");List<Integer> list2 = Arrays.asList(1  , 2  , 3 , 4  ,  5 , 6  ,7  ,  8 , 9  ,10  , 11 ,12 , 13 , 14);Map<String,Object> hashMap = new HashMap<>();Map<String,Object> treeMap = new TreeMap<>();Map<String,Object> linkedHashMap = new LinkedHashMap<>();Map<Integer,Object> treeMap2 = new TreeMap<>();for (int i = 0; i < list1.size(); i++) {hashMap.put(list1.get(i), list2.get(i));treeMap.put(list1.get(i), list2.get(i));linkedHashMap.put(list1.get(i), list2.get(i));treeMap2.put(list2.get(i), list1.get(i));}List<String> list5 = new ArrayList<>();List<String> list6 = new ArrayList<>();Iterator<Map.Entry<String, Object>> it = hashMap.entrySet().iterator();while(it.hasNext()){Map.Entry<String, Object> entry = it.next();String key = entry.getKey();String value = String.valueOf(entry.getValue());list5.add(key);list6.add(value);}System.out.println("hashMap:"+"无序案例");System.out.println("hashMap:"+hashMap);System.out.println("list5ap:"+list5);System.out.println("list6ap:"+list6);System.out.println("--------------------------------------------------");List<String> list7 = new ArrayList<>();List<String> list8 = new ArrayList<>();Iterator<Map.Entry<String, Object>> it2 = treeMap.entrySet().iterator();while(it2.hasNext()){Map.Entry<String, Object> entry = it2.next();String key = entry.getKey();String value = String.valueOf(entry.getValue());list7.add(key);list8.add(value);}System.out.println("treeMap:"+"无序案例");System.out.println("treeMap:"+treeMap);System.out.println("list7ap:"+list7);System.out.println("list8ap:"+list8);System.out.println("--------------------------------------------------");List<String> list9 = new ArrayList<>();List<String> list10 = new ArrayList<>();Iterator<Map.Entry<String, Object>> it3 = linkedHashMap.entrySet().iterator();while(it3.hasNext()){Map.Entry<String, Object> entry = it3.next();String key = entry.getKey();String value = String.valueOf(entry.getValue());list9.add(key);list10.add(value);}System.out.println("linkedHashMap:"+"有序案例");System.out.println("linkedHashMap:"+linkedHashMap);System.out.println("list9dHashMap:"+list9);System.out.println("list10dHashMap:"+list10);System.out.println("--------------------------------------------------");List<String> list11 = new ArrayList<>();List<String> list12 = new ArrayList<>();Iterator<Map.Entry<Integer,Object>> it4 = treeMap2.entrySet().iterator();while(it4.hasNext()){Map.Entry<Integer,Object> entry = it4.next();Integer key = entry.getKey();String value = String.valueOf(entry.getValue());list11.add(key.toString());list12.add(value);}System.out.println("treeMap2:"+"有序案例");System.out.println("treeMap2:"+treeMap2);System.out.println("list11ap:"+list11);System.out.println("list12ap:"+list12);}
}

测试输出：

hashMap:无序案例
hashMap:{流=9, 黄=1, 来=7, 天=5, 上=6, 之=3, 不=12, 复=13, 到=10, 河=2, 水=4, 奔=8, 海=11, 回=14}
list5ap:[流, 黄, 来, 天, 上, 之, 不, 复, 到, 河, 水, 奔, 海, 回]
list6ap:[9, 1, 7, 5, 6, 3, 12, 13, 10, 2, 4, 8, 11, 14]
--------------------------------------------------
treeMap:无序案例
treeMap:{上=6, 不=12, 之=3, 到=10, 回=14, 复=13, 天=5, 奔=8, 来=7, 水=4, 河=2, 流=9, 海=11, 黄=1}
list7ap:[上, 不, 之, 到, 回, 复, 天, 奔, 来, 水, 河, 流, 海, 黄]
list8ap:[6, 12, 3, 10, 14, 13, 5, 8, 7, 4, 2, 9, 11, 1]
--------------------------------------------------
linkedHashMap:有序案例
linkedHashMap:{黄=1, 河=2, 之=3, 水=4, 天=5, 上=6, 来=7, 奔=8, 流=9, 到=10, 海=11, 不=12, 复=13, 回=14}
list9dHashMap:[黄, 河, 之, 水, 天, 上, 来, 奔, 流, 到, 海, 不, 复, 回]
list10dHashMap:[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
--------------------------------------------------
treeMap2:有序案例
treeMap2:{1=黄, 2=河, 3=之, 4=水, 5=天, 6=上, 7=来, 8=奔, 9=流, 10=到, 11=海, 12=不, 13=复, 14=回}
list11ap:[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]
list12ap:[黄, 河, 之, 水, 天, 上, 来, 奔, 流, 到, 海, 不, 复, 回]