HashMap, LinkedHashMap和TreeMap在Java中的区别是什么?
我在输出中没有看到任何不同，因为这三个都有keySet和values。什么是哈希表?
Map m1 = new HashMap();
m1.put("map", "HashMap");
m1.put("schildt", "java2");
m1.put("mathew", "Hyden");
m1.put("schildt", "java2s");
print(m1.keySet());
print(m1.values());
SortedMap sm = new TreeMap();
sm.put("map", "TreeMap");
sm.put("schildt", "java2");
sm.put("mathew", "Hyden");
sm.put("schildt", "java2s");
print(sm.keySet());
print(sm.values());
LinkedHashMap lm = new LinkedHashMap();
lm.put("map", "LinkedHashMap");
lm.put("schildt", "java2");
lm.put("mathew", "Hyden");
lm.put("schildt", "java2s");
print(lm.keySet());
print(lm.values());
三者中最重要的是如何保存条目的顺序。
HashMap -不保存条目的顺序。
如。
public static void main(String[] args){
HashMap<String,Integer> hashMap = new HashMap<>();
hashMap.put("First",1);// First ---> 1 is put first in the map
hashMap.put("Second",2);//Second ---> 2 is put second in the map
hashMap.put("Third",3); // Third--->3 is put third in the map
for(Map.Entry<String,Integer> entry : hashMap.entrySet())
{
System.out.println(entry.getKey()+"--->"+entry.getValue());
}
}
LinkedHashMap:它保存条目的顺序。例如:
public static void main(String[] args){
LinkedHashMap<String,Integer> linkedHashMap = new LinkedHashMap<>();
linkedHashMap.put("First",1);// First ---> 1 is put first in the map
linkedHashMap.put("Second",2);//Second ---> 2 is put second in the map
linkedHashMap.put("Third",3); // Third--->3 is put third in the map
for(Map.Entry<String,Integer> entry : linkedHashMap.entrySet())
{
System.out.println(entry.getKey()+"--->"+entry.getValue());
}
}
TreeMap:按键的升序保存条目。例如:
public static void main(String[] args) throws IOException {
TreeMap<String,Integer> treeMap = new TreeMap<>();
treeMap.put("A",1);// A---> 1 is put first in the map
treeMap.put("C",2);//C---> 2 is put second in the map
treeMap.put("B",3); //B--->3 is put third in the map
for(Map.Entry<String,Integer> entry : treeMap.entrySet())
{
System.out.println(entry.getKey()+"--->"+entry.getValue());
}
}
