Java集合Map集合之TreeMap

//TreeMap的自然排序是字典排序
Map<Integer,String> map = new TreeMap<Integer,String>();
map.put(4,"a");
map.put(3,"a");
map.put(2,"a");
map.put(1,"a");
System.out.println(map);

Map<String,String> map1 = new TreeMap<String,String>();
map1.put("A","B");
map1.put("C","C");
map1.put("B","D");
map1.put("D","E");
System.out.println(map1);