Write a program that use a loop to display the integers entered by the user from smallest to larger

where the user enter a series of integers in a loop. The user enter -99 to signal the end of the series.Where all of the integer will be save in a file. After all the numbers have been entered, the program should read all of the integers save in the file and display all of numbers from smallest to largest.

I been trying but I just cant figure out, how to display the integers in order.Now I'm stuck. Please help! and thank you, I'm still a beginner.

package chapter4;

import java.util.Scanner;

import java.io.*;

import java.util.Random;

public class ProChallenge10 {

    public static void main(String[]args) throws IOException{

        int integer =0; //Integer enter by the user.

        boolean signal = false; // To end the loop.

        Scanner keyboard = new Scanner(System.in);

        //Created the file for the integers entered. 
        PrintWriter outputFile = new PrintWriter("ProChallenge10.txt"); 

        //Let the user enter a series of numbers.
        while(signal == false){

            System.out.println("Enter an integer");
            integer = keyboard.nextInt();

            outputFile.println(integer);

        //To end the program.
        if(integer == -99){
            signal = true;
            //Close the outputFile.
            outputFile.close();
            } 
        }

         //Open the file and read input from the file.
         File file = new File("ProChallenge10.txt");
         Scanner inputFile = new Scanner(file);

         //Read all of the values from the file and display their numbers. 
         while(inputFile.hasNext()){

            int number = inputFile.nextInt();

           }
         //Close the InputFile.
         inputFile.close();
    }
}