How to transfer a value from one JLabel to another?

Question

I have this calculator working, but I can\'t figure out how to get the value in the resultpane to the first textbox when you click the \"finish\" button.

Answer 1

Give your ResultPane a new public method that allows you to extract the text from its JLabel, something like:

  public String getResultText() {
     return result.getText();
  }

And then call it when you want to get the text of that field:

  public class ToText1Action extends AbstractAction {
     public ToText1Action() {
        putValue(NAME, "Finish");
     }

     @Override
     public void actionPerformed(ActionEvent e) {
         String resultText = resultPane.getResultText();
         double number = // extract number from resultText
         firstNumberField.setText(number);
     }
  }

Better still, simply store the latest result value in a double variable that is an instance field of the class, say called lastResult and set the firstNumberField with that.

Note that you should not have empty catch blocks.

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Edit

For example:

public class CalculatorPane extends JPanel {
  private final ResultPane resultPane;
  private final JLabel firstNumberLabel = new JLabel("First Number:");
  private final JLabel secondNumberLabel = new JLabel("Second Number:");
  private final JTextField firstNumberField = new JTextField(5);
  private final JTextField secondNumberField = new JTextField(5);

  private double result = 0.0;   // ****** declared here

  // ***** etc..... *****

  public class DivideAction extends AbstractAction {

     public DivideAction() {
        putValue(NAME, "/");
     }

     @Override
     public void actionPerformed(ActionEvent e) {
        try {
           double num1 = Double.parseDouble(firstNumberField.getText());
           double num2 = Double.parseDouble(secondNumberField.getText());

           result = num1 / num2; // ****** note variable not declared
           resultPane.setResult(result);
        } catch (NumberFormatException exp) {
           // show error message
           // set text fields to "0"
        }
     }

  }

  public class ToText1Action extends AbstractAction {
     public ToText1Action() {
        super("Finish");
        putValue(MNEMONIC_KEY, KeyEvent.VK_F);
     }

     @Override
     public void actionPerformed(ActionEvent e) {
        firstNumberField.setText(String.format("%.2f", result));
     }
  }