Find the Largest Number Using Comparator in Java

A program that I wrote that will arrange the given series of numbers and find the largest in terms of value using comparator library in Java. 

I hope you will find my work useful and beneficial. If you have some questions about programming, about my work please send mu an email at jakerpomperada@gmail.com and jakerpomperada@yahoo.com. People here in the Philippines can contact me at  my mobile number 09173084360.

Thank you very much and Happy Programming.

Program Sample Output

Program Listing

Solution.java

package exam;

import java.util.*;

public class Solution {

    private static Comparator<Integer> sorter = new Comparator<Integer>(){

        @Override

        public int compare(Integer a, Integer b){

            String a1 = a.toString();

            String b1 = b.toString();

            if(a1.length() == b1.length()){

                return b1.compareTo(a1);

            }

            int mlen = Math.max(a1.length(), b1.length());

            while(a1.length() < mlen * 2) a1 += a1;

            while(b1.length() < mlen * 2) b1 += b1;

            return b1.compareTo(b1);

        }

    };

    public static String join_all(List<?> things){

        String output = "";

        for(Object obj:things){

            output += obj;

        }

        return output;

    }

    public static void main(String[] args){

        List<Integer> num_values1 = new ArrayList<Integer>(Arrays.asList(2,1,3));

        List<Integer> num_values2 = new ArrayList<Integer>(Arrays.asList(1,4,7));

        List<Integer> num_values3 = new ArrayList<Integer>(Arrays.asList(4,8,3));

        List<Integer> num_values4 = new ArrayList<Integer>(Arrays.asList(4,6,3));

        

        System.out.println();

        System.out.print("Find the Largest Number Using Comparator in Java");

        System.out.println("\n\n");

        Collections.sort(num_values1, sorter);

        System.out.println(join_all(num_values1));

        

        System.out.println();

        Collections.sort(num_values2, sorter);

        System.out.println(join_all(num_values2));

        

        System.out.println();

        Collections.sort(num_values3, sorter);

        System.out.println(join_all(num_values3));

        

        System.out.println();

        Collections.sort(num_values4, sorter);

        System.out.println(join_all(num_values4));

        

    }

}