原文： https://beginnersbook.com/2014/07/how-to-get-the-sub-map-from-treemap-example-java/

在这个例子中，我们将看到如何从TreeMap获取子映射。我们正在使用TreeMap类的subMap()方法。有关详细信息，请参阅以下程序中的注释。

示例

  1. import java.util.*;
  3. class TreeMapDemo {
  4.   public static void main(String args[]) {
  6.     // Create a TreeMap
  7.     TreeMap<String, String> treemap = 
  8.             new TreeMap<String, String>();
  10.     // Put elements to the map
  11.     treemap.put("Key1", "Jack");
  12.     treemap.put("Key2", "Rick");
  13.     treemap.put("Key3", "Kate");
  14.     treemap.put("Key4", "Tom");
  15.     treemap.put("Key5", "Steve");
  16.     treemap.put("Key6", "Ram");
  18.     // Displaying TreeMap elements
  19.     System.out.println("TreeMap Contains : " + treemap);
  21.     // Getting the sub map
  22.     /* public SortedMap<K,V> subMap(K fromKey,K toKey): Returns 
  23.      * a view of the portion of this map whose keys range from 
  24.      * fromKey, inclusive, to toKey, exclusive. 
  25.      * (If fromKey and toKey are equal, the returned map is empty.) 
  26.      * The returned map is backed by this map, so changes in the 
  27.      * returned map are reflected in this map, and vice-versa. 
  28.      * The returned map supports all optional map operations that 
  29.      * this map supports.
  30.      */
  31.     SortedMap<String, String> sortedMap = treemap.subMap("Key2","Key5");
  32.     System.out.println("SortedMap Contains : " + sortedMap);
  34.     // Removing an element from Sub Map
  35.     sortedMap.remove("Key4");
  37.     /* Displaying elements of original TreeMap after 
  38.      * removing an element from the Sub Map. Since Sub Map is 
  39.      * backed up by original Map, the element should be removed
  40.      * from this TreeMap too.
  41.      */
  42.     System.out.println("TreeMap Contains : " + treemap);
  43.   }
  44. }

输出：

  1. TreeMap Contains : {Key1=Jack, Key2=Rick, Key3=Kate, Key4=Tom, Key5=Steve, Key6=Ram}
  2. SortedMap Contains : {Key2=Rick, Key3=Kate, Key4=Tom}
  3. TreeMap Contains : {Key1=Jack, Key2=Rick, Key3=Kate, Key5=Steve, Key6=Ram}

参考：

subMap()方法 - TreeMap javadoc)
SortedMap javadoc