Java，不显示输出？

任务是显示用户的全名、随机偶数和首字母

比如说。约书亚·伊桑·保罗·史密斯

史密斯JEPS320

当我按下“获取代码”按钮时，什么也没发生，这是为什么

package pack;
import javax.swing.JOptionPane;
import java.math.*;



public class saf extends javax.swing.JFrame {



    public saf() {
        initComponents();
    }


    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        btnfullname = new javax.swing.JButton();
        txaDisplay = new javax.swing.JScrollPane();
        TxaDisplay = new javax.swing.JTextArea();
        btnrandomGenerator = new javax.swing.JButton();
        btnCode = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        btnfullname.setText("Enter");
        btnfullname.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnfullnameActionPerformed(evt);
            }
        });

        TxaDisplay.setEditable(false);
        TxaDisplay.setColumns(20);
        TxaDisplay.setRows(5);
        txaDisplay.setViewportView(TxaDisplay);

        btnrandomGenerator.setText("Generate Random Number");
        btnrandomGenerator.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnrandomGeneratorActionPerformed(evt);
            }
        });

        btnCode.setText("Get Code!");
        btnCode.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnCodeActionPerformed(evt);
            }
        });

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap(54, Short.MAX_VALUE)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                        .addComponent(txaDisplay, javax.swing.GroupLayout.PREFERRED_SIZE, 353, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addGap(40, 40, 40))
                    .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                        .addComponent(btnrandomGenerator)
                        .addGap(112, 112, 112))
                    .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                        .addComponent(btnCode)
                        .addGap(165, 165, 165))
                    .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                        .addComponent(btnfullname)
                        .addGap(177, 177, 177))))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(19, 19, 19)
                .addComponent(btnfullname)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addComponent(txaDisplay, javax.swing.GroupLayout.PREFERRED_SIZE, 142, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addComponent(btnrandomGenerator)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addComponent(btnCode)
                .addContainerGap(28, Short.MAX_VALUE))
        );

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

    private void btnfullnameActionPerformed(java.awt.event.ActionEvent evt) {                                            
    String fullname = JOptionPane.showInputDialog("Enter your full name:");

    TxaDisplay.append(fullname);
    }                                           

    private void btnrandomGeneratorActionPerformed(java.awt.event.ActionEvent evt) {                                                   
    int randnum; //Code for a 3 digit even number
    do
    {
       randnum=(int)(Math.random()*900)+100; 
    }
    while(randnum%2!=0);
    TxaDisplay.append("" + randnum);
    }                                                  

    private void btnCodeActionPerformed(java.awt.event.ActionEvent evt) {                                        
    int randnum = 0 ;
    String fullname = "" ;
    String initials ="";
    int posSpc = fullname.lastIndexOf(" ");
    String surname = fullname.substring(posSpc+1, fullname.length());
    initials = initials + fullname.charAt(0);
    for(int i =0; i< fullname.length() ; i++)
    {
        char ch=fullname.charAt(i);
            if(ch==' ')
            {
                initials = initials + fullname.charAt(i+1);

            }
    }
    String code = surname + initials + "" + randnum;
    TxaDisplay.append(fullname+"\n");
    TxaDisplay.append(code);

    }                                       

    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 ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(saf.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(saf.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(saf.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(saf.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 saf().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JTextArea TxaDisplay;
    private javax.swing.JButton btnCode;
    private javax.swing.JButton btnfullname;
    private javax.swing.JButton btnrandomGenerator;
    private javax.swing.JScrollPane txaDisplay;
    // End of variables declaration                   
}

包装；
导入javax.swing.JOptionPane；
导入java.math.*；
公共类saf扩展了javax.swing.JFrame{
公共安全部队（）{
初始化组件（）；
}
@抑制警告（“未选中”）
//                           
私有组件（）{
btnfullname=newjavax.swing.JButton（）；
txaDisplay=newjavax.swing.JScrollPane（）；
TxaDisplay=newjavax.swing.JTextArea（）；
btnrandomGenerator=newjavax.swing.JButton（）；
btnCode=newjavax.swing.JButton（）；
setDefaultCloseOperation（javax.swing.WindowConstants.EXIT_ON_CLOSE）；
btnfullname.setText（“输入”）；
btnfullname.addActionListener（新java.awt.event.ActionListener（）{
public void actionPerformed（java.awt.event.ActionEvent evt）{
btnfullnameActionPerformed（evt）；
}
});
TxaDisplay.setEditable（false）；
TxaDisplay.setColumns（20）；
TxaDisplay.setRows（5）；
setViewportView（txaDisplay）；
setText（“生成随机数”）；
btnrandomGenerator.addActionListener（新java.awt.event.ActionListener（）{
public void actionPerformed（java.awt.event.ActionEvent evt）{
btnrandomGeneratorActionPerformed（evt）；
}
});
setText（“获取代码！”）；
btnCode.addActionListener（新的java.awt.event.ActionListener（）{
public void actionPerformed（java.awt.event.ActionEvent evt）{
执行的BTN决策（evt）；
}
});
javax.swing.GroupLayout=newjavax.swing.GroupLayout（getContentPane（））；
getContentPane（）.setLayout（布局）；
layout.setHorizontalGroup(
createParallelGroup（javax.swing.GroupLayout.Alignment.LEADING）
.addGroup（layout.createSequentialGroup（）
.addContainerGap（54，简称最大值）
.addGroup（layout.createParallelGroup（javax.swing.GroupLayout.Alignment.LEADING）
.addGroup（javax.swing.GroupLayout.Alignment.TRAILING，layout.createSequentialGroup（）
.addComponent（txaDisplay，javax.swing.GroupLayout.PREFERRED_SIZE，353，javax.swing.GroupLayout.PREFERRED_SIZE）
.addGap（40,40,40））
.addGroup（javax.swing.GroupLayout.Alignment.TRAILING，layout.createSequentialGroup（）
.add组件（btnrandomGenerator）
.addGap（112、112、112））
.addGroup（javax.swing.GroupLayout.Alignment.TRAILING，layout.createSequentialGroup（）
.addComponent（btnCode）
.addGap（165、165、165））
.addGroup（javax.swing.GroupLayout.Alignment.TRAILING，layout.createSequentialGroup（）
.addComponent（btnfullname）
.addGap（177177177）））
);
layout.setVerticalGroup(
createParallelGroup（javax.swing.GroupLayout.Alignment.LEADING）
.addGroup（layout.createSequentialGroup（）
.addGap（19,19,19）
.addComponent（btnfullname）
.addPreferredGap（javax.swing.LayoutStyle.ComponentPlacement.RELATED）
.addComponent（txaDisplay，javax.swing.GroupLayout.PREFERRED_SIZE，142，javax.swing.GroupLayout.PREFERRED_SIZE）
.addPreferredGap（javax.swing.LayoutStyle.ComponentPlacement.UNRELATED）
.add组件（btnrandomGenerator）
.addPreferredGap（javax.swing.LayoutStyle.ComponentPlacement.RELATED）
.addComponent（btnCode）
.addContainerGap（28，简称最大值））
);
包装（）；
}//                         
私有void btnfullnameActionPerformed（java.awt.event.ActionEvent evt）{
String fullname=JOptionPane.showInputDialog（“输入您的全名：”）；
TxaDisplay.append（全名）；
}                                           
private void btnrandomGeneratorActionPerformed（java.awt.event.ActionEvent evt）{
int randnum；//3位偶数的代码
做
{
randnum=（int）（Math.random（）*900）+100；
}
而（随机数%2！=0）；
TxaDisplay.append（“+randnum”）；
}                                                  
私有void btnCodeActionPerformed（java.awt.event.ActionEvent evt）{
int randnum=0；
字符串fullname=“”；
字符串首字母=”；
int posSpc=fullname.lastIndexOf（“”）；
字符串姓氏=fullname.substring（posSpc+1，fullname.length（））；
缩写=缩写+全名.charAt（0）；
对于（int i=0；iint randnum = 0 ;
String fullname = "" ;// Here empty string !!!
String initials ="";
int posSpc = fullname.lastIndexOf(" "); // this is always -1
String surname = fullname.substring(posSpc+1, fullname.length()); // This is the empty string
initials = initials + fullname.charAt(0); // That throws a StringIndexOutOfBoundsException

public class saf extends javax.swing.JFrame {

    private String fullname;


    public saf() {
        initComponents();
    }


    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        btnfullname = new javax.swing.JButton();
        txaDisplay = new javax.swing.JScrollPane();
        TxaDisplay = new javax.swing.JTextArea();
        btnrandomGenerator = new javax.swing.JButton();
        btnCode = new javax.swing.JButton();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        btnfullname.setText("Enter");
        btnfullname.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnfullnameActionPerformed(evt);
            }
        });

        TxaDisplay.setEditable(false);
        TxaDisplay.setColumns(20);
        TxaDisplay.setRows(5);
        txaDisplay.setViewportView(TxaDisplay);

        btnrandomGenerator.setText("Generate Random Number");
        btnrandomGenerator.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnrandomGeneratorActionPerformed(evt);
            }
        });

        btnCode.setText("Get Code!");
        btnCode.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnCodeActionPerformed(evt);
            }
        });

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap(54, Short.MAX_VALUE)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                        .addComponent(txaDisplay, javax.swing.GroupLayout.PREFERRED_SIZE, 353, javax.swing.GroupLayout.PREFERRED_SIZE)
                        .addGap(40, 40, 40))
                    .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                        .addComponent(btnrandomGenerator)
                        .addGap(112, 112, 112))
                    .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                        .addComponent(btnCode)
                        .addGap(165, 165, 165))
                    .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                        .addComponent(btnfullname)
                        .addGap(177, 177, 177))))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(19, 19, 19)
                .addComponent(btnfullname)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addComponent(txaDisplay, javax.swing.GroupLayout.PREFERRED_SIZE, 142, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addComponent(btnrandomGenerator)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
                .addComponent(btnCode)
                .addContainerGap(28, Short.MAX_VALUE))
        );

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

    private void btnfullnameActionPerformed(java.awt.event.ActionEvent evt) {                                            
    fullname = JOptionPane.showInputDialog("Enter your full name:");

    TxaDisplay.append(fullname);
    }                                           

    private void btnrandomGeneratorActionPerformed(java.awt.event.ActionEvent evt) {                                                   
    int randnum; //Code for a 3 digit even number
    do
    {
       randnum=(int)(Math.random()*900)+100; 
    }
    while(randnum%2!=0);
    TxaDisplay.append("" + randnum);
    }                                                  

    private void btnCodeActionPerformed(java.awt.event.ActionEvent evt) {                        
    if(fullname==null||fullname.trim().isEmpty()) {
          return;
    }
    int randnum = 0 ;
    String initials =;
    int posSpc = fullname.lastIndexOf(" ");
    String surname = fullname.substring(posSpc+1, fullname.length());
    initials = fullname.charAt(0);
    for(int i =0; i< fullname.length() ; i++)
    {
        char ch=fullname.charAt(i);
            if(ch==' ')
            {
                initials = initials + fullname.charAt(i+1);

            }
    }
    String code = surname + initials + "" + randnum;
    TxaDisplay.append(fullname+"\n");
    TxaDisplay.append(code);

    }                                       

    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 ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(saf.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(saf.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(saf.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(saf.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 saf().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JTextArea TxaDisplay;
    private javax.swing.JButton btnCode;
    private javax.swing.JButton btnfullname;
    private javax.swing.JButton btnrandomGenerator;
    private javax.swing.JScrollPane txaDisplay;
    // End of variables declaration                   
}