Может я слепой, но не вижу в упор ))
package com.javarush.task.task08.task0828;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.Map;
import java.util.HashMap;
import java.util.List;
import java.util.Set;
/*
Номер месяца
*/
public class Solution {
public static void main(String[] args) throws IOException {
BufferedReader hren = new BufferedReader(new InputStreamReader(System.in));
String fuker = hren.readLine();
HashMap<String, Integer> date = new HashMap<>();
date.put("January",1);
date.put("February",2);
date.put("Marсh",3);
date.put("April",4);
date.put("May",5);
date.put("June",6);
date.put("July",7);
date.put("August",8);
date.put("September",9);
date.put("October",10);
date.put("November",11);
date.put("December",12);
for (Map.Entry<String, Integer> hers : date.entrySet())
{
String s = hers.getKey();
int y = hers.getValue();
if (s.equalsIgnoreCase(fuker))
System.out.println(s + " is the " + y + " month");
}
}
}