如何遍历TreeMap的PORTION？

Posted 2021-04-08

我正在进行一项任务，我必须搜索TreeMap中的键（映射到它们所在的文件。基本上，这个TreeMap是一个倒置索引），它以我们在程序中指定的查询字开头。一个查询文件。但是，为了提高效率，我的教授不希望在查找以查询词开头的键时迭代TreeMap中的所有键，而是希望我们只迭代我们需要迭代的键。例如，如果查询单词以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想法吗？

答案

使用TreeMap的subMap()方法获取一个SortedMap，它只包含您要检查的键范围。然后遍历该SortedMap。

另一答案

以下是@ottomeister建议的基本实现：

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 => def