为什么我的 Java 程序会打开两个实例/窗口？

Question

I am trying to make a simple BlackJack game/project for school. So far when I run it - everything goes well, but two instances / JFrame windows are opened instead of just one. Here is the code for the gameloop which is in a class called (BlackJackProject). Below this code i have also put the code for the JFrame form/file which is opening two windows.

public class BlackJackProject {

public static int final_total_cards = 0;
public static int total_cards = 0;

/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
    // TODO code application logic here

   int turns = 3;

   boolean isGameOver = false;
       while(isGameOver = true){
           turns --;
           if (turns > 0){
               Hit_Or_Stand.main(null);
           }
           else{
               break;
           }
       }
   }
}

Here is the code for the file which is opening two windows

public class Hit_Or_Stand extends javax.swing.JFrame {

   int turns = 3;

   String name = null;
   int balance = 5000;
   int bet_amount = 0;
   String name_and_choice_question = JOptionPane.showInputDialog(null, "What is your name?");
   String ask_bet_amount = JOptionPane.showInputDialog(null, "Your balance is: " + balance + "Enter your bet amount");

public Hit_Or_Stand() {
    initComponents();
     lblOption.setText(name_and_choice_question + ", what would you like to do?");
}

/**
 * This method is called from within the constructor to initialize the form.
 * WARNING: Do NOT modify this code. The content of this method is always
 * regenerated by the Form Editor.
 */
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">                          
private void initComponents() {

    jPanel1 = new javax.swing.JPanel();
    lblOption = new javax.swing.JLabel();
    btn_Hit = new javax.swing.JButton();
    btn_Stand = new javax.swing.JButton();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

    lblOption.setText("da");

    btn_Hit.setFont(new java.awt.Font("Tahoma", 0, 14)); // NOI18N
    btn_Hit.setText("Hit");
    btn_Hit.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            btn_HitActionPerformed(evt);
        }
    });

    javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
    jPanel1.setLayout(jPanel1Layout);
    jPanel1Layout.setHorizontalGroup(
        jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(jPanel1Layout.createSequentialGroup()
            .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING)
                .addGroup(jPanel1Layout.createSequentialGroup()
                    .addContainerGap()
                    .addComponent(btn_Hit, javax.swing.GroupLayout.PREFERRED_SIZE, 97, javax.swing.GroupLayout.PREFERRED_SIZE))
                .addGroup(javax.swing.GroupLayout.Alignment.LEADING, jPanel1Layout.createSequentialGroup()
                    .addGap(175, 175, 175)
                    .addComponent(lblOption)))
            .addContainerGap(299, Short.MAX_VALUE))
    );
    jPanel1Layout.setVerticalGroup(
        jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(jPanel1Layout.createSequentialGroup()
            .addGap(35, 35, 35)
            .addComponent(lblOption)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 308, Short.MAX_VALUE)
            .addComponent(btn_Hit, javax.swing.GroupLayout.PREFERRED_SIZE, 52, javax.swing.GroupLayout.PREFERRED_SIZE))
    );

    btn_Stand.setFont(new java.awt.Font("Tahoma", 0, 14)); // NOI18N
    btn_Stand.setText("Stand");

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addComponent(btn_Stand, javax.swing.GroupLayout.PREFERRED_SIZE, 97, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addGap(0, 81, Short.MAX_VALUE))
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING)
                .addComponent(btn_Stand, javax.swing.GroupLayout.PREFERRED_SIZE, 52, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addComponent(jPanel1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
            .addGap(0, 101, Short.MAX_VALUE))
    );

    pack();
}// </editor-fold>                        

private void btn_HitActionPerformed(java.awt.event.ActionEvent evt) {                                        


    if (final_total_cards < 21){ 
       int card_draw = (int)(Math.random() * 6 + 1);
       total_cards = total_cards + card_draw;
       final_total_cards = total_cards + card_draw;
       JOptionPane.showMessageDialog(null, "Your total card value is: " + final_total_cards);


    }else if (final_total_cards == 21){

        JOptionPane.showMessageDialog(null, "Your total card value is: " + final_total_cards);
        JOptionPane.showMessageDialog(null, "You win!");

        balance = balance + Integer.parseInt(ask_bet_amount);
        JOptionPane.showMessageDialog(null, "Your final balance is : " + balance);
            this.dispose();





    }

    else if (final_total_cards > 21){

        JOptionPane.showMessageDialog(null, "Your total card value is: " + final_total_cards);
        JOptionPane.showMessageDialog(null, "You lose!");

        balance = balance - Integer.parseInt(ask_bet_amount);
        JOptionPane.showMessageDialog(null, "Your final balance is: " + balance);




    }

}                                       

/**
 * @param args the command line arguments
 */
public static void main(String args[]) {
    /* Set the Nimbus look and feel */
    //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
    /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
     * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
     */
    try {
        for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
            if ("Windows".equals(info.getName())) {
                javax.swing.UIManager.setLookAndFeel(info.getClassName());
                break;
            }
        }
    } catch (ClassNotFoundException ex) {
        java.util.logging.Logger.getLogger(Hit_Or_Stand.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(Hit_Or_Stand.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(Hit_Or_Stand.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(Hit_Or_Stand.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }
    //</editor-fold>



    /* Create and display the form */
    java.awt.EventQueue.invokeLater(new Runnable() {
        public void run() {
            new Hit_Or_Stand().setVisible(true);
        }
    });





}



// Variables declaration - do not modify                     
private javax.swing.JButton btn_Hit;
private javax.swing.JButton btn_Stand;
private javax.swing.JPanel jPanel1;
public static javax.swing.JLabel lblOption;
// End of variables declaration                   

}

Answer 1

The problem is this block:

   while(isGameOver = true){
       turns --;
       if (turns > 0){
           Hit_Or_Stand.main(null);
       }
       else{
           break;
       }
   }

A couple of issues:

while (isGameOver = true)

You're not comparing but assigning isGameOver to true . This should be == but in that case you'd never enter the loop because you instantiated the variable to false and never change the value.

       turns --;
       if (turns > 0){
           Hit_Or_Stand.main(null);
       }
       else{
           break;
       }

You start with turns = 3 and decrease it (new value 2 ). Hit_Or_Stand.main(null) will return immediately after it's setting up the JFrame . So you will have the next iteration immediately, decrease turns again (now it's 1 ), open another window. After that turns is decreased again (new value is now 0 ) and because turns is now no longer > 1 you leave the while -loop.

To tell you more about how to solve that problem, depends on what you actually want to achieve, so you might edit your question accordingly.