Java getText NullPointerException

Question

I spend about 2 hours trying to understand why my code keeps throwing runtime errors. It doesn't want to accept user inputs... I'm pretty sure my implementaion of getext is correct. Could you guys take a look at my code and help me see what I did wrong?

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

public class Mdt1 extends JFrame implements ActionListener{

/**
 * 
 */
private static final long serialVersionUID = 1L;
/**
 * @param args
 */
 JTextField twager, dcard1, dcard2, pcard1, pcard2;

public Mdt1()  {
    JFrame blackjack = new JFrame();
    Border wwager = BorderFactory.createTitledBorder("Wager");
    JPanel pwager = new JPanel();
    pwager.setBorder(wwager);
    JLabel lwager = new JLabel("Enter wager:");
    JTextField twager = new JTextField(6);
    twager.addActionListener(this);
    pwager.add(lwager);
    pwager.add(twager);

    JPanel pplayer = new JPanel();
    Border wayer = BorderFactory.createTitledBorder("Player");
    pplayer.setLayout(new BoxLayout(pplayer, BoxLayout.Y_AXIS));
    pplayer.setBorder(wayer);
    pplayer.setSize(100, 100);
    JTextField pcard1 = new JTextField(6);
    pcard1.setEditable(false);
    JTextField pcard2 = new JTextField(6);
    pcard2.setEditable(false);
    pplayer.add(pcard1);
    pplayer.add(pcard2);


    JPanel pdealer = new JPanel();
    Border wealer = BorderFactory.createTitledBorder("Dealer");
    pdealer.setLayout(new BoxLayout(pdealer, BoxLayout.Y_AXIS));
    pdealer.setBorder(wealer);
    pdealer.setSize(100, 100);
    JTextField dcard1 = new JTextField(6);
    dcard1.setEditable(false);
    JTextField dcard2 = new JTextField(6);
    dcard2.setEditable(false);
    pdealer.add(dcard1);
    pdealer.add(dcard2);

    JPanel cards = new JPanel();
    Border wards = BorderFactory.createTitledBorder("Cards");
    cards.setBorder(wards);
    cards.setSize(220, 80);
    cards.add(pplayer);
    cards.add(pdealer);

    JPanel pendgame = new JPanel();
    Border wesult = BorderFactory.createTitledBorder("Endgame");
    pendgame.setBorder(wesult);



    blackjack.setLayout(new BorderLayout());
    blackjack.setVisible(true);
    blackjack.setSize(200, 200);
    blackjack.setTitle("♣ Blackjack ♠");
    blackjack.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    blackjack.add(pwager, BorderLayout.NORTH);
    blackjack.add(cards);
    blackjack.pack();
    blackjack.setResizable(false);

}

public void actionPerformed(ActionEvent e) {
    String swager = twager.getText();
    double wager;
    int  dealer1, dealer2, player1, player2;
    int  dealervalue1, dealervalue2, playervalue1, playervalue2;
    int  dealerTotal, playerTotal;


    wager = Double.parseDouble(swager);

    Random r=new Random();
    // card faces
    dealer1=r.nextInt(13) + 1;
    String sdealer1 = Integer.toString(dealer1);
    dealer2=r.nextInt(13) + 1;
    String sdealer2 = Integer.toString(dealer2);
    player1=r.nextInt(13) + 1;
    String splayer1 = Integer.toString(player1);
    player2=r.nextInt(13) + 1;
    String splayer2 = Integer.toString(player2);
    // Show dealer's card faces
    switch(dealer1)
    {
    case 1: dcard1.setText("Ace "); break;
    case 11: dcard1.setText("Jack"); break;
    case 12: dcard1.setText("Queen"); break;
    case 13: dcard1.setText("King"); break;
    default: dcard1.setText(sdealer1); break; 
    } 
    switch(dealer2)
    {
    case 1: dcard2.setText("Ace"); break;
    case 11: dcard2.setText("Jack"); break;
    case 12: dcard2.setText("Queen"); break;
    case 13: dcard2.setText("King"); break;
    default: dcard2.setText(sdealer2); break;
    } 
    // Show player's card faces
    switch(player1)
    {
    case 1: System.out.print("Ace"); break;
    case 11: System.out.print("Jack"); break;
    case 12: System.out.print("Queen"); break;
    case 13: System.out.print("King"); break;
    default: System.out.print(splayer1); break;
    } 
    switch(player2)
    {
    case 1: System.out.println("Ace"); break;
    case 11: System.out.println("Jack"); break;
    case 12: System.out.println("Queen"); break;
    case 13: System.out.println("King"); break;
    default: System.out.println(splayer2); break;
    } 
    // Determine card values
    dealervalue1 = dealer1; 
    switch(dealer1)
    {
    case 1:  dealervalue1=11; break;
    case 11:  case 12:  case 13:
        dealervalue1=10;  break;
    } // switch
    dealervalue2 = dealer2; 
    switch(dealer2)
    {
    case 1:  dealervalue2=11; break;
    case 11:  case 12:  case 13:
        dealervalue2=10;  break;
    } // switch
    dealerTotal = dealervalue1+dealervalue2;
    if (dealerTotal == 22)      dealerTotal = 12;
    playervalue1 = player1; 
    switch(player1)
    {
    case 1:  playervalue1=11; break;
    case 11:  case 12:  case 13:
        playervalue1=10;  break;
    } // switch
    playervalue2 = player2; 
    switch(player2)
    {
    case 1:  playervalue2=11; break;
    case 11:  case 12:  case 13:
        playervalue2=10;  break;
    } // switch
    playerTotal = playervalue1+playervalue2;
    if (playerTotal == 22)
        playerTotal = 12;
    if (playerTotal == 21)
    { 
        wager = wager * 1.5;
        JOptionPane.showMessageDialog(null, "You have a Blackjack!!! \n You won: $" + wager);

        return;
    }
    if (playerTotal >= dealerTotal)
    {
        System.out.println("" + wager);
        return;
    }
    JOptionPane.showMessageDialog(null, "You lost: $" + wager, "You lost!",  JOptionPane.ERROR_MESSAGE);

    System.out.println(swager);
} 

public static void main(String[] args) {
    // TODO Auto-generated method stub
    /**
     * 2
     * 2-card Blackjack game
     */
    Mdt1 black = new Mdt1();
}// main

}

KV Prajapati · Accepted Answer · 2011-10-13 14:18:56Z

4

You have instance fields - JTextField twager, dcard1, dcard2, pcard1, pcard2; however in method Mdt1() you stored references of JTextField into local reference variable.

public Mdt1()  {
    JFrame blackjack = new JFrame();
    Border wwager = BorderFactory.createTitledBorder("Wager");
    JPanel pwager = new JPanel();
    pwager.setBorder(wwager);
    JLabel lwager = new JLabel("Enter wager:");
 //   JTextField twager = new JTextField(6); //<---  Local variable
    twager = new JTextField(6);              //<--- correction
    twager.addActionListener(this);
    pwager.add(lwager);
    pwager.add(twager);
    ....
}

answered Oct 13, 2011 at 14:18

KV Prajapati

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Comments

Perception · Accepted Answer · 2011-10-13 14:20:57Z

3

You hid your class instance variable twager with another variable with the same name in your constructor. In effect, you never initialized your class instance.

answered Oct 13, 2011 at 14:20

Perception

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Comments

Ewald · Accepted Answer · 2011-10-13 14:22:41Z

1

In your constructor, you are redeclaring the variables you have as class variables.

Your class variables are JTextField twager, dcard1, dcard2, pcard1, pcard2;

In the constructor called Mdt1(), where you initialize these variables, you create them locally.

For example, the line JTextField twager = new JTextField(6); should be changed to twager= new JTextField(6); if you want the problem fixed.

That should fix the problem.

answered Oct 13, 2011 at 14:22

Ewald

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