program guesses the number you're thinking of between 1000-9999

I'm doing a program which has to guess the number you're thinking of between 1000-9999 in less than 20 guesses. So far, this is what I've got. It gives me the error:

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 4500, Size: 4500
at java.util.ArrayList.rangeCheck(Unknown Source)
at java.util.ArrayList.get(Unknown Source)
at GuessingGame.updateMyGuess(GuessingGame.java:52)
at GuessingGame.main(GuessingGame.java:124)
not sure why!

this is my program:

import java.util.ArrayList;
import javax.swing.JOptionPane;
public class GuessingGame {
  
  public int total; // keeps track of number of guesses made
  public static int myguess = 0; 
  public ArrayList<String> guesses; // creat the arraylist
  
  
  public GuessingGame ( ) {
	  
	//initialize array with capacity 9000 
	guesses = new ArrayList<String>(9000); 
    
	//fills up array list with numbers 1000 through to 9999 
    for(int i = 0; i < 9000; i++) {
       guesses.add(Integer.toString(1000+i));
  }
  }
  
  public int myGuessIs() {
    
	 //guess is invalid when the array list is empty (i.e. the size is 0) 
    if(guesses.size()==0){
      return -1;
    }
    //randomly picks a number thats left in the array list
    int guess1 = Integer.parseInt(guesses.get((int)(Math.random()*guesses.size())));
    
    total++;
    return guess1;
  }
  
  public int totalNumGuesses() {
    //returns the number of guesses made
    return total;
  }
  
  public void updateMyGuess(int nmatches) {
    //removes the guess itself, and other impossible numbers from the ArrayList
   

	 String  myGuess2= Integer.toString(myguess);
	 int matches = 0; 
	  for(int i = 0; i<guesses.size(); i++) {
		 //for(int j = 0; j<guesses.size(); j++ ){
		  
		  if(nmatches!=matches||((guesses.get(i)).equals(myGuess2))){
			  guesses.remove(i);
			
		  		}
			 for(int k = 0; k<4; k++){
				 if(myGuess2.charAt(k)==(guesses.get(i)).charAt(k)){
					  matches++; 
					 			}
			 }
			  
		  }
			  
		 
	  }

  
	

  
 
 
  
  public static void main(String[] args) {
    
    GuessingGame gamer = new GuessingGame();
    
    JOptionPane.showMessageDialog(null, "Think of a number between 1000 and 9999.\n Click OK when you are ready...", "Let's play a game", JOptionPane.INFORMATION_MESSAGE);
    int numMatches = 0;
    
    
    do {
      myguess = gamer.myGuessIs();
      if (myguess == -1) {
        JOptionPane.showMessageDialog(null, "I don't think your number exists.\n I could be wrong though...", "Mistake", JOptionPane.INFORMATION_MESSAGE);
        System.exit(0);
      }
      String userInput = JOptionPane.showInputDialog("I guess your number is " + myguess + ". How many digits did I guess correctly?");
      // quit if the user input nothing (such as pressed ESC)
      if (userInput == null)
        System.exit(0);
      // parse user input, pop up a warning message if the input is invalid
      try {
        numMatches = Integer.parseInt(userInput.trim());
      }
      catch(Exception exception) {
        JOptionPane.showMessageDialog(null, "Your input is invalid. Please enter a number between 0 and 4", "Warning", JOptionPane.WARNING_MESSAGE);
        continue;
      }
      // the number of matches must be between 0 and 4
      if (numMatches < 0 || numMatches > 4) {
        JOptionPane.showMessageDialog(null, "Your input is invalid. Please enter a number between 0 and 4", "Warning", JOptionPane.WARNING_MESSAGE);
        continue;
      }
      if (numMatches == 4)
        break;
      // update based on user input
      gamer.updateMyGuess(numMatches);
      
    } while (true);
    
    // the game ends when the user says all 4 digits are correct
    System.out.println("Aha, I got it, your number is " + myguess + ".");
    System.out.println("I did it in " + gamer.totalNumGuesses() + " turns.");
    
  }
}