HashMap通过value反查key

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;

  }

}