Java Elo

Elo.java

import java.lang.Math;

public class Elo {
  public int k;
  
  public Elo(int k) {
    this.k = k;
  }
  
  public double expectedScoreForDifference(int difference) {
    return 1 / (1 + Math.pow(10, (difference / 400)));
  }
  
  public double expectedScore(int playerElo, int opponentElo) {
    return this.expectedScoreForDifference(opponentElo - playerElo);
  }
  
  public int update(int playerElo, int opponentElo, boolean playerWon) {
    double actualScore = 0.0;
    if (playerWon) {
      actualScore = 1.0;
    }
    double expectedScore = this.expectedScore(playerElo, opponentElo);
    return (int)Math.round(playerElo + this.k * (actualScore-expectedScore));
  }

  public static void main(String[] args) {
    Elo e = new Elo(32);
    System.out.println("Player[1200] vs. Opponent[1200], player wins: " +
      e.update(1200, 1200, true));
    System.out.println("Player[1200] vs. Opponent[1600], player wins: " +
      e.update(1200, 1600, true));
    System.out.println("Player[1600] vs. Opponent[1200], oponent wins: " +
      e.update(1600, 1200, false));
    System.out.println("Player[1200] vs. Opponent[2000], player wins: " +
      e.update(1200, 2000, true));
  }
}

output.txt

Downloads:$ javac Elo.java && java Elo
Player[1200] vs. Opponent[1200], player wins: 1216
Player[1200] vs. Opponent[1600], player wins: 1229
Player[1600] vs. Opponent[1200], oponent wins: 1571
Player[1200] vs. Opponent[2000], player wins: 1232