I am to make a simple calculator but I am having issues with this:

When the button is pressed it should do the following:

• Get the text from the two JTextFields and convert them to Doubles. Use Double.parseDouble(String input) to turn a String into a Double. (Not sure where to put this?)
• Get the text from the JComboBox. Use the getSelectedItem() method to get the currently selected string. (Not sure if I did this correctly)
• Calculate the result based on the string from the JComboBox This determines if you will use the operator, - operator, * operator or / operator. (do not know how to do this)
• Set the result to the JLabel Use the .setText() method to construct a String

These are my 4 problems.

class MyFrame extends JFrame {

public JTextField firstNumber;
public JTextField secondNumber;
public JButton calc;
public JLabel result;
public JComboBox combo;

public MyFrame() {
    super();
    init();
}

private void init() {
    
    JButton calc = new JButton("Calculate");
    calc.addActionListener(new MyButtonListener(this));
    firstNumber = new JTextField();
    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    this.add(calc);
    this.add(firstNumber);
    this.add(secondNumber);
    this.pack();
    this.setVisible(true);
}
}

class MyButtonListener implements ActionListener {
MyFrame fr;

public MyButtonListener(MyFrame frame)
{
    fr = frame;
    fr.firstNumber.getText();
    fr.secondNumber.getText();
    fr.combo.getSelectedItem();
}


public void actionPerformed(ActionEvent e) 
{
    JButton btn = (JButton) e.getSource();
    
}
}

private static void constructGUI() {

JFrame.setDefaultLookAndFeelDecorated(true);

JTextField firstNumber = new JTextField();
JTextField secondNumber = new JTextField();
JButton calc = new JButton("Calculate"); 
JLabel result = new JLabel();
JFrame frame = new JFrame();

frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setTitle("Simple Calculator");


 String[] arth = { "Add", "Subtract", "Multiple", 
 "Divide" };
 JComboBox combo = new JComboBox(arth);
 combo.setSelectedIndex(0);

frame.setLayout(new GridLayout(5, 2));
frame.add(new JLabel("First Number:"));
frame.add(firstNumber);
frame.add(new JLabel("Second Number:"));
frame.add(secondNumber);
frame.add(combo);
frame.add(calc);
frame.add(new JLabel("Result:"));
frame.pack();
frame.setSize(200, 200);
frame.setVisible(true);
}   


public static void main(String[] args) 
{
SwingUtilities.invokeLater(new Runnable() 
{
    public void run() 
    {
        constructGUI();
    }   
});
}
}

CodePudding user response：

Your MyFrame is not connected with the rest of the code invoked in main.

1. Added listener to your result field (also included in JFrame because it was not used) - code from lambda can be extracted for better visibility

2. Added only "ADD" rest will be similar

   private static void constructGUI() {

   JFrame.setDefaultLookAndFeelDecorated(true);
   
   JTextField firstNumber = new JTextField();
   JTextField secondNumber = new JTextField();
   JButton calc = new JButton("Calculate");
   JLabel result = new JLabel("Result:");
   JFrame frame = new JFrame();
   
   frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   frame.setTitle("Simple Calculator");
   
   String[] arth = {"Add", "Subtract", "Multiple", "Divide"};
   JComboBox combo = new JComboBox(arth);
   combo.setSelectedIndex(0);
   
   frame.setLayout(new GridLayout(5, 2));
   frame.add(new JLabel("First Number:"));
   frame.add(firstNumber);
   frame.add(new JLabel("Second Number:"));
   frame.add(secondNumber);
   frame.add(combo);
   frame.add(calc);
   frame.add(result);
   frame.pack();
   frame.setSize(200, 200);
   frame.setVisible(true);
   
   calc.addActionListener(
       e -> {
         var first = Double.parseDouble(firstNumber.getText());
         var secound = Double.parseDouble(secondNumber.getText());
         double res = 0;
   
         switch (Objects.requireNonNull(combo.getSelectedItem()).toString()) {
           case "Add":
             res = first   secound;
             break;
         }
         result.setText(String.valueOf(res));
       });
   

   }

Simplified main:

public static void main(String[] args) {
    SwingUtilities.invokeLater(Main2::constructGUI);
  }