Rps.java

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Rps extends JFrame
        implements ActionListener {

    private final char moves[] = {'R', 'P', 'S'};
    private JRadioButton rock, paper, scissors;
    private JTextField display;

    public Rps() {
        super("Rock, paper, Scissors");

        rock = new JRadioButton("   Rock   ", true);
        paper = new JRadioButton("   Paper  ");
        scissors = new JRadioButton(" Scissors ");

        ButtonGroup rpsButtons = new ButtonGroup();
        rpsButtons.add(rock);
        rpsButtons.add(paper);
        rpsButtons.add(scissors);

        JButton go = new JButton("         Go         ");
        go.addActionListener(this);

        display = new JTextField(25);
        display.setEditable(false);
        display.setBackground(Color.yellow);

        Container c = getContentPane();
        c.setLayout(new FlowLayout());
        c.add(rock);
        c.add(paper);
        c.add(scissors);
        c.add(go);
        c.add(display);
    }

    /**
     * returns -1 if the player wins, 0 if it's a tie, and 1 if the computer
     * wins
     */
    private int nextPlay(char computerMove, char playerMove) {
        switch (computerMove) {
            case 'R':
                switch (playerMove) {
                    case 'R':
                        return 0;
                    case 'P':
                        return -1;
                    case 'S':
                        return 1;
                }
            case 'P':
                switch (playerMove) {
                    case 'R':
                        return 1;
                    case 'P':
                        return 0;
                    case 'S':
                        return -1;
                }
            case 'S':
                switch (playerMove) {
                    case 'R':
                        return -1;
                    case 'P':
                        return 1;
                    case 'S':
                        return 0;
                }
        }
        return 0;
    }

    public void actionPerformed(ActionEvent e) {
        char playerMove, computerMove;
        if (rock.isSelected()) {
            playerMove = 'R';
        } else if (paper.isSelected()) {
            playerMove = 'P';
        } else // if (scissors.isSelected())
        {
            playerMove = 'S';
        }

        int k = (int) (Math.random() * 3);
        computerMove = moves[k];
        int result = nextPlay(computerMove, playerMove);

        String msg = "  You said " + makeWord(playerMove) + ", I said "
                + makeWord(computerMove);
        if (result < 0) {
            msg += " -- you win.";
        } else if (result == 0) {
            msg += " -- tie.";
        } else // if (result > 0)
        {
            msg += " -- I win.";
        }
        display.setText(msg);
    }

    private String makeWord(char move) {
        String word = "";

        switch (move) {
            case 'R':
                word = "ROCK";
                break;
            case 'P':
                word = "PAPER";
                break;
            case 'S':
                word = "SCISSORS";
                break;
        }
        return word;
    }

    public static void main(String[] args) {
        Rps window = new Rps();
        window.setBounds(300, 300, 300, 140);
        window.setDefaultCloseOperation(EXIT_ON_CLOSE);
        window.setVisible(true);
    }
}