[Java] Check the number of occurrences of characters

table of contents

--Introduction --Premise ――What you want to achieve ――What I tried --Problem


Suddenly, I want to study Map and List! !! I thought </ b>, so I thought about the issues and made it. I stumbled upon the roles of Map and List and conversion. Even if I searched online, I couldn't find any good results, so I've put together my own, so I'll write an article.


――What you want to achieve --Identification of the most frequently used string for n arbitrary string type inputs (n_1 n_2 n_3 ... ... n). ――What I tried --Implemented [key: input string, value: number of appearances] as Map <String, Integer> map = Map () ;. --Sort the map by [value] and retrieve the very first [key]!

--Problem --Map system [HashMap, LinkedHashMap, TreeMap] basically has no order of elements. --Like map [0], you cannot retrieve the value by index.

  • Solution --You can get the combination of map key and value by using Map.Entry class. --You can store Entry objects in List and sort by Entry value of List [i].

Implementation details

The contents implemented based on the solution are as follows.


import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Scanner;

public class CountMain {

	public static void main(String[] args) {

		//Input detection
		Scanner sc = new Scanner(System.in);
		String count = sc.nextLine();
		String[] line = sc.nextLine().split(" ");

		//Map making
		Map<String, Integer> map = new HashMap<String, Integer>();
		for(int i=0; i<line.length; i++){
				map.put(line[i], 1);
			} else {
				int tmp = map.get(line[i]);
				map.put(line[i], tmp+1);

		//Get map entry → store in list
		List<Entry<String, Integer>> list = new ArrayList<Entry<String, Integer>>();
		for (Map.Entry<String, Integer> entry : map.entrySet()){

		//Compare the value of entry in list → sort
		for (int i = 0; i < list.size(); i++){
			for (int j = list.size()-1; j > i; j--){
				if (list.get(j).getValue() > list.get(j-1).getValue()){
					Map.Entry<String, Integer> tmpEntry = list.get(j-1);
					list.set(j-1, list.get(j));
					list.set(j, tmpEntry);
		try {
			int i = 1;
			while( list.get(i).getValue() == list.get(i-1).getValue() ){
				System.out.print(" " + list.get(i).getKey());
		} catch (IndexOutOfBoundsException e){
		} finally {

At the end

--Summary ――It is important to be aware of the role of each class --Map throws a function to List when an associative array or an ordered array is needed ――Because I couldn't do this, I didn't understand when I first tried to sort the Map.

  • Future tasks --The sort in the list is done by human-powered bubble sort, but it seems that Collection.sort () can be used. --Something like Comparator <> seems to be useful. --Reference link below
    • https://www.sejuku.net/blog/16176
    • http://lovedvoraklayout.hatenablog.com/entry/java-map-value-sort-2
    • https://teratail.com/questions/117328

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