HashMap,LinkedHashMap,TreeMap对比

相同点：

HashMap,LinkedHashMap,TreeMap都属于Map；用于存储键值对（key-value），根据键得到值。键不允许重复，值允许重复。

不同点：

HashMap根据键的HashCode为索引存储数据。键值对取出时是随机的。
TreeMap键值对取出是排序的。
LinkedHashMap是HashMap的子类。键值对输入顺序和取出顺序是相同的。
测试代码：

public class MapTest {

public static void main(String[] args) {
try {
hashMapTest();
treeMapTest();
likedHashMapTest();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

public static void hashMapTest() throws Exception {
System.out.println("--------HashMap--------");
Map<String, String> map = new HashMap<String, String>();
map.put("1", "map test 1");
map.put("2", "map test 2");
map.put("3", "map test 3");
map.put("a", "map test a");
map.put("b", "map test b");
map.put("c", "map test c");
Iterator<Entry<String, String>> it = map.entrySet().iterator();
while (it.hasNext()) {
Entry<String, String> entry = it.next();
System.out.println("Key: " + entry.getKey() + "   Value: "
+ entry.getValue());
}
}

public static void treeMapTest() throws Exception {
System.out.println("--------TreeMap--------");
Map<String, String> map = new TreeMap<String, String>();
map.put("1", "map test 1");
map.put("2", "map test 2");
map.put("3", "map test 3");
map.put("a", "map test a");
map.put("b", "map test b");
map.put("c", "map test c");
Iterator<Entry<String, String>> it = map.entrySet().iterator();
while (it.hasNext()) {
Entry<String, String> entry = it.next();
System.out.println("Key: " + entry.getKey() + "   Value: "
+ entry.getValue());
}
}

public static void likedHashMapTest() throws Exception {
System.out.println("--------LikedHashMap--------");
Map<String, String> map = new LinkedHashMap<String, String>();
map.put("1", "map test 1");
map.put("2", "map test 2");
map.put("3", "map test 3");
map.put("a", "map test a");
map.put("b", "map test b");
map.put("c", "map test c");
Iterator<Entry<String, String>> it = map.entrySet().iterator();
while (it.hasNext()) {
Entry<String, String> entry = it.next();
System.out.println("Key: " + entry.getKey() + "   Value: "
+ entry.getValue());
}
}
}

结果：
--------HashMap--------

Key: 1   Value: map test 1

Key: a   Value: map test a

Key: 2   Value: map test 2

Key: b   Value: map test b

Key: 3   Value: map test 3

Key: c   Value: map test c

--------TreeMap--------

Key: 1   Value: map test 1

Key: 2   Value: map test 2

Key: 3   Value: map test 3

Key: a   Value: map test a

Key: b   Value: map test b

Key: c   Value: map test c

--------LikedHashMap--------

Key: 1   Value: map test 1

Key: 2   Value: map test 2

Key: 3   Value: map test 3

Key: a   Value: map test a

Key: b   Value: map test b

Key: c   Value: map test c