如何遍历TreeMap的一部分？

Question

我正在做一个分配，我必须搜索TreeMap中的键（映射到它们被发现的文件。基本上，这个TreeMap是一个反转索引），它以一个查询单词开始，程序在查询文件中。但是，为了提高效率，我们的教授不希望在查找以查询词开头的键时遍历TreeMap中的所有键，而是希望我们只遍历我们需要遍历的键。例如，如果查询词以C开头，那么我们应该只遍历以C开头的键。有关如何处理这个问题的任何想法？

Answer 1

使用TreeMap的subMap()方法来获取SortedMap，其中只包含您想要检查的键的范围。然后遍历SortedMap。

Answer 2

下面是基本实现什么@ottomeister建议：

public class Tester{ 
    public static void main(String a[]){ 
     TreeMap<CustomObject,String> tm = new TreeMap<CustomObject,String>(); 
     tm.put(new CustomObject(4,"abc"),"abc"); 
     tm.put(new CustomObject(7,"bcd"),"bcd"); 
     tm.put(new CustomObject(25,"cde"),"cde"); 
     tm.put(new CustomObject(18,"def"),"def"); 
     tm.put(new CustomObject(2,"efg"),"efg"); 
     tm.put(new CustomObject(8,"fgh"),"fgh"); 
     tm.put(new CustomObject(3,"aab"),"aab"); 
     tm.put(new CustomObject(13,"aab"),"abb"); 

     Map<CustomObject, String> sub = tm.subMap(new CustomObject(9,""),new CustomObject(20,"")); 

     for(Map.Entry<CustomObject,String> entry : sub.entrySet()) { 
      CustomObject key = entry.getKey(); 
      String value = entry.getValue(); 

      System.out.println(key.getId() + " => " + value); 
     } 
    } 
} 

class CustomObject implements Comparable<CustomObject>{ 
    private int id; 
    private String Name; 
    CustomObject(int id, String Name){ 
     this.id = id; 
     this.Name = Name; 
    } 
    @Override 
    public int compareTo(@NotNull CustomObject o) { 
     return this.id - o.id; 
    } 
    public int getId(){ 
     return this.id; 
    } 
} 

输出： 13 => ABB 18 =>高清