Java

So I'm writing a Rock Papper Scissors program for my programming class.

/*
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package lab4;

/**
 *
 * @author LAPPY
 */
// ****************************************************************
//   Rock.java
//
//   Play Rock, Paper, Scissors with the user
//
// ****************************************************************
import java.util.Scanner;
import java.util.Random;

public class Rock
{
    public static void main(String[] args)
    {
    String personPlay;    //User's play -- "R", "P", or "S"

    String computerPlay = null;  //Computer's play -- "R", "P", or "S"
                          //Randomly generated number used to determine
    int computerInt;      //Randomly generated number used to determine
                          //computer's play

        Scanner scan = new Scanner(System.in);
    Random generator = new Random();




    computerInt = generator.nextInt (3); //Generate computer's play (0,1,2)





    //Translate computer's randomly generated play to string
    switch (computerInt)


        {
            case 0:
                computerPlay = "R";
                break;
            case 1:
                computerPlay = "P";
                break;
            case 2:
                computerPlay = "S";
                break;

    }


        //Get player's play from input-- note that this is stored as a string
        System.out.println ("Enter your play: R, P, or S");

        personPlay = scan.nextLine();



    //Make player's play uppercase for ease of comparison
        personPlay.toUpperCase();



    //Print computer's play
        System.out.println ("Computer play is " + computerPlay);



    //See who won.  Use nested ifs instead of &&.
    if (personPlay.equals(computerPlay))
        System.out.println("It's a tie!");
    else if (personPlay.equals("R"))
        if (computerPlay.equals("S"))
        System.out.println("Rock crushes scissors.  You win!!");
            else if(computerPlay.equals("P"))
                System.out.println("Paper covers rock. You lose!!");
        if(personPlay.equals("P"))
            if (computerPlay.equals("S"))
                System.out.println("Scissors cut paper. You lose!!");
            else if(computerPlay.equals("R"))
                System.out.println("Paper covers rock. You win!!");
       if (personPlay.equals("S"))
            if (computerPlay.equals("R"))
                System.out.println("Rock crushes scissors.  You lose!!");
            else if(computerPlay.equals("P"))
                System.out.println("Scissors cut paper. You win!!");


    }
}

The problem is, the "personPlay.toUpperCase();" won't do anything at all. I have to enter an uppercase letter as if that command isn't there.

What am I missing?

Oh hi I done your homework.

import java.util.*;

public class RPS {
    public static void main(String[] args) {
        RPS rps = new RPS();
        while(rps.run());
    }
    private static final int ROCK = 0;
    private static final int PAPER = 1;
    private static final int SCISSORS = 2;
    private int[][] adjacency = new int[][]{
        {0, 2, 1},
        {1, 0, 2},
        {2, 1, 0}
    };
    private String[] names = new String[]{"Rock", "Paper", "Scissors"};
    private String[] actions = new String[]{"Crushes", "Covers", "Cut"};
    private String[] results = new String[]{"It's a tie!", "You win!!", "You lose!!"};
    private Random r;
    private Scanner sc;
    private Map<String, Integer> m;
    public RPS() {
        r = new Random();
        sc = new Scanner(System.in);
        m = new HashMap<String, Integer>();
        m.put("R", ROCK);
        m.put("P", PAPER);
        m.put("S", SCISSORS);
    }
    public boolean run() {
        System.out.println("Enter your play: R, P, or S");
        Integer player = null;
        while(player == null) player = m.get(sc.nextLine().trim().toUpperCase());
        int computer = r.nextInt(3);
        System.out.println("Computers play is: " + names[computer]);
        if(adjacency[player][computer] == 0) System.out.println(results[0]);
        else if(adjacency[player][computer] == 1) System.out.println(names[player] + " " + actions[player] + " " + names[computer] + ". " + results[1]);
        else System.out.println(names[computer] + " " + actions[computer] + " " + names[player] + ". " + results[2]);
        return true;
    }
}