Java—Map浅入

Posted 2022-07-13 michaelcnblogs

写支付签名的时候遇到了Map一家，就简单的比较了一下，于是乎先打印看看结果

Map<String,String> hashMap1 = new HashMap<>();
hashMap1.put("d","1");
hashMap1.put("e","2");
hashMap1.put("c","3");
hashMap1.put("b","4");
hashMap1.put("a","5");
for (Map.Entry<String, String> entry : hashMap1.entrySet()) 
    System.out.println("hashMap1:     Key = " + entry.getKey() + ", Value = " + entry.getValue());

System.out.println("------------------------------------------------------------------------------------------");
Map<String,String> linkedHashMap = new LinkedHashMap<>();
linkedHashMap.put("d","1");
linkedHashMap.put("e","2");
linkedHashMap.put("c","3");
linkedHashMap.put("b","4");
linkedHashMap.put("a","5");
for (Map.Entry<String, String> entry : linkedHashMap.entrySet()) 
    System.out.println("linkedHashMap:     Key = " + entry.getKey() + ", Value = " + entry.getValue());

System.out.println("------------------------------------------------------------------------------------------");


Map<String,String> treeMap = new TreeMap<>();
treeMap.put("d","1");
treeMap.put("e","2");
treeMap.put("c","3");
treeMap.put("b","4");
treeMap.put("a","5");
for (Map.Entry<String, String> entry : treeMap.entrySet()) 
    System.out.println("treeMap:     Key = " + entry.getKey() + ", Value = " + entry.getValue());



打印结果如下

hashMap1: Key = a, Value = 5
hashMap1: Key = b, Value = 4
hashMap1: Key = c, Value = 3
hashMap1: Key = d, Value = 1
hashMap1: Key = e, Value = 2
------------------------------------------------------------------------------------------
linkedHashMap: Key = d, Value = 1
linkedHashMap: Key = e, Value = 2
linkedHashMap: Key = c, Value = 3
linkedHashMap: Key = b, Value = 4
linkedHashMap: Key = a, Value = 5
------------------------------------------------------------------------------------------
treeMap: Key = a, Value = 5
treeMap: Key = b, Value = 4
treeMap: Key = c, Value = 3
treeMap: Key = d, Value = 1
treeMap: Key = e, Value = 2

 

 

乍一看 hashMap 与 treeMap貌似没啥区别，可能是值设置的太简单了存在偶然性，于是乎

改了一下

 

Map<String,Object> hashMap2 = new HashMap<String,Object>();
hashMap2.put("1a", "a");
hashMap2.put("2", "b");
hashMap2.put("4a", "d");
hashMap2.put("3", "c");
hashMap2.put("2a", "d");
hashMap2.put("3a", "c");
for(Map.Entry<String, Object> entry : hashMap2.entrySet())
    System.out.println("hashMap2:     Key = " + entry.getKey() + ", Value = " + entry.getValue());

System.out.println("------------------------------------------------------------------------------------------");

Map<String,Object> linkedHashMap2 = new LinkedHashMap<>();
linkedHashMap2.put("1a", "a");
linkedHashMap2.put("2", "b");
linkedHashMap2.put("4a", "d");
linkedHashMap2.put("3", "c");
linkedHashMap2.put("2a", "d");
linkedHashMap2.put("3a", "c");
for(Map.Entry<String, Object> entry : linkedHashMap2.entrySet())
    System.out.println("linkedHashMap2:     Key = " + entry.getKey() + ", Value = " + entry.getValue());


System.out.println("------------------------------------------------------------------------------------------");
Map<String,Object> treeMap2 = new TreeMap<>();
treeMap2.put("1a", "a");
treeMap2.put("2", "b");
treeMap2.put("4a", "d");
treeMap2.put("3", "c");
treeMap2.put("2a", "d");
treeMap2.put("3a", "c");
for(Map.Entry<String, Object> entry : treeMap2.entrySet())
    System.out.println("treeMap2:     Key = " + entry.getKey() + ", Value = " + entry.getValue());

打印结果果然不一样了

hashMap2: Key = 1a, Value = a
hashMap2: Key = 2, Value = b
hashMap2: Key = 3, Value = c
hashMap2: Key = 4a, Value = d
hashMap2: Key = 3a, Value = c
hashMap2: Key = 2a, Value = d
------------------------------------------------------------------------------------------
linkedHashMap2: Key = 1a, Value = a
linkedHashMap2: Key = 2, Value = b
linkedHashMap2: Key = 4a, Value = d
linkedHashMap2: Key = 3, Value = c
linkedHashMap2: Key = 2a, Value = d
linkedHashMap2: Key = 3a, Value = c
------------------------------------------------------------------------------------------
treeMap2: Key = 1a, Value = a
treeMap2: Key = 2, Value = b
treeMap2: Key = 2a, Value = d
treeMap2: Key = 3, Value = c
treeMap2: Key = 3a, Value = c
treeMap2: Key = 4a, Value = d

 

 

综上简单的来看，只有treeMap做了排序

hashMap看心情排序

linkedHashMap按照插入顺序排序

简单的理解就这么多，代码是写完了，有时间深入

欢迎留言，指正不足