java HashMap通过value反查key的代码示例

import java.util.arraylist;
import java.util.hashmap;
import java.util.iterator;
import java.util.map;
import java.util.set;
public class mapvaluegetkey {
  public static void main(string[] args) {
    map map = new hashmap<>();
    map.put(1,"a");
    map.put(2,"a");
    map.put(3,"a");
    map.put(4,"a");
    map.put(5,"a");

    string value = "a";
    arraylist arr = valuegetkey(map, value);
    if(!arr.isempty()) {
      for(int i=0; i<arr.size(); i++) {
        system.out.println(arr.get(i));
      }
    }

  }
  private static arraylist valuegetkey(map map,string value) {
    set set = map.entryset();
    arraylist arr = new arraylist<>();
    iterator it = set.iterator();
    while(it.hasnext()) {
      map.entry entry = (map.entry)it.next();
      if(entry.getvalue().equals(value)) {
        int s = (int)entry.getkey();
        arr.add(s);
      }
    }
    return arr;
  }
}

结果如下：

1
2
3
4
5