how to get the text from a text field to a variable?

Question

i want to get the value from the txt field val1 and val2 and store it in the variables n1 and n2. then n1 and n2 will be parsed to get the value for the calculator. here is the code:

    public class CalcUI extends javax.swing.JFrame {
    String n1 = val1.getText();
    String n2 = val2.getText();
    double num1 = Double.parseDouble(n1);
    double num2 = Double.parseDouble(n2); 

/**
 * Creates new form CalcUI
 */
public CalcUI() {

    initComponents();
}

/**
 * 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() {

    val1 = new javax.swing.JTextField();
    val2 = new javax.swing.JTextField();
    plus = new javax.swing.JButton();
    multiply = new javax.swing.JButton();
    clr = new javax.swing.JButton();
    exit = new javax.swing.JButton();
    minus = new javax.swing.JButton();
    divide = new javax.swing.JButton();
    ans = new javax.swing.JLabel();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

    plus.setText("+");
    plus.setMaximumSize(new java.awt.Dimension(41, 41));
    plus.setMinimumSize(new java.awt.Dimension(41, 41));
    plus.setPreferredSize(new java.awt.Dimension(41, 41));
    plus.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            plusActionPerformed(evt);
        }
    });

    multiply.setText("*");
    multiply.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            multiplyActionPerformed(evt);
        }
    });

    clr.setText("Clear");
    clr.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            clrActionPerformed(evt);
        }
    });

    exit.setText("Exit");
    exit.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            exitActionPerformed(evt);
        }
    });

    minus.setText("-");
    minus.setMaximumSize(new java.awt.Dimension(41, 41));
    minus.setMinimumSize(new java.awt.Dimension(41, 41));
    minus.setPreferredSize(new java.awt.Dimension(41, 41));
    minus.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            minusActionPerformed(evt);
        }
    });

    divide.setText("/");
    divide.setMaximumSize(new java.awt.Dimension(41, 41));
    divide.setMinimumSize(new java.awt.Dimension(41, 41));
    divide.setPreferredSize(new java.awt.Dimension(41, 41));
    divide.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            divideActionPerformed(evt);
        }
    });

    ans.setBorder(javax.swing.BorderFactory.createEtchedBorder());

    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()
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(val1)
                .addComponent(val2)
                .addGroup(layout.createSequentialGroup()
                    .addComponent(clr)
                    .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                    .addComponent(exit)))
            .addContainerGap())
        .addGroup(layout.createSequentialGroup()
            .addGap(134, 134, 134)
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING, false)
                .addComponent(multiply, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addComponent(plus, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
            .addGap(77, 77, 77)
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(minus, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                .addComponent(divide, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
            .addGap(143, 143, 143))
        .addGroup(layout.createSequentialGroup()
            .addContainerGap()
            .addComponent(ans, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
            .addContainerGap())
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(layout.createSequentialGroup()
            .addGap(46, 46, 46)
            .addComponent(val1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addGap(18, 18, 18)
            .addComponent(val2, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
            .addComponent(ans, javax.swing.GroupLayout.PREFERRED_SIZE, 23, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addGap(26, 26, 26)
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(plus, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addComponent(minus, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
            .addGap(34, 34, 34)
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(multiply, javax.swing.GroupLayout.PREFERRED_SIZE, 41, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addComponent(divide, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 31, Short.MAX_VALUE)
            .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(clr)
                .addComponent(exit))
            .addContainerGap())
    );

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

private void plusActionPerformed(java.awt.event.ActionEvent evt) {                                     
    double add = num1 + num2;
    ans.setText(Double.toString(add));
         // TODO add your handling code here:
}                                    

private void minusActionPerformed(java.awt.event.ActionEvent evt) {                                      
    double min = num1 - num2;
    ans.setText(Double.toString(min));                                     
   // TODO add your handling code here:
}                                     

private void divideActionPerformed(java.awt.event.ActionEvent evt) {                                       
    double div = num1 / num2;
    ans.setText(Double.toString(div));
       // TODO add your handling code here:
}                                      

private void exitActionPerformed(java.awt.event.ActionEvent evt) {                                     
    System.exit(0);
      // TODO add your handling code here:
}                                    

private void clrActionPerformed(java.awt.event.ActionEvent evt) {                                    
       val1.setText("");
        val2.setText("");
           ans.setText("");
        // TODO add your handling code here:
}                                   

private void multiplyActionPerformed(java.awt.event.ActionEvent evt) {                                         
    double mult = num1 * num2;
    ans.setText(Double.toString(mult));   
        // TODO add your handling code here:
}                                        

/**
 * @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 ("Nimbus".equals(info.getName())) {
                javax.swing.UIManager.setLookAndFeel(info.getClassName());
                break;
            }
        }
    } catch (ClassNotFoundException ex) {
        java.util.logging.Logger.getLogger(CalcUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(CalcUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(CalcUI.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(CalcUI.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 CalcUI().setVisible(true);
        }
    });
}
// Variables declaration - do not modify
private javax.swing.JLabel ans;
private javax.swing.JButton clr;
private javax.swing.JButton divide;
private javax.swing.JButton exit;
private javax.swing.JButton minus;
private javax.swing.JButton multiply;
private javax.swing.JButton plus;
private javax.swing.JTextField val1;
private javax.swing.JTextField val2;
// End of variables declaration

}

the problem is that in the declaration

String n1 = val1.getText();
String n2 = val2.getText();

i get an error whioch says illegal forward reference. how do i fix this?

this was fixed.

now when i use the following code:

    public class CalcUI extends javax.swing.JFrame {

Double num1 ; Double num2 ;

/**
 * Creates new form CalcUI
 */

public CalcUI(){
    val1 = new javax.swing.JTextField();
    val2 = new javax.swing.JTextField();

    num1 = Double.parseDouble(val1.getText());
    num2 = Double.parseDouble(val2.getText()); 

    initComponents();
}

i get a build error which says:

    Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: empty String
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1011)
at java.lang.Double.parseDouble(Double.java:540)
at CalcUI.<init>(CalcUI.java:24)
at CalcUI$7.run(CalcUI.java:227)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:701)
at java.awt.EventQueue.access$000(EventQueue.java:102)
at java.awt.EventQueue$3.run(EventQueue.java:662)
at java.awt.EventQueue$3.run(EventQueue.java:660)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:671)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)

how do i fix this? what is wrong with the code?

Answer 1

If you use this code you will see what your input is.

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

JOptionPane.showMessageDialog(null,yourTextField.getText());

}

So, this should store your data to n1.

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

String n1;                                   
n1 = yourTextField.getText();

}

Answer 2

You're missing the "equals" button that will do the computation. Add a listener to that button, and in the listener's actionPerformed() you getText() and then compute the calculation. Also, I guess there's no need to have n1 and n2 as class-level variables.

Answer 3

I imagine your JTextField components will not have been initialised by the time you are calling:

String n1 = val1.getText();
String n2 = val2.getText();