Swing integer division with error dialogs

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.Locale;

public class Main {

javax.swing supplies buttons, labels, panels and frames. java.awt supplies layouts, colours and fonts. java.awt.event supplies listener/event types. Locale is available where text formatting needs it. Main matches the source filename.

    static JPanel root(String title) {
        for(String key:new String[]{"Label.font","Button.font","RadioButton.font","CheckBox.font","TextField.font","TextArea.font","ComboBox.font"})UIManager.put(key,new Font(Font.SANS_SERIF,Font.PLAIN,18));

root configures the selected UIManager font keys to an 18-point sans-serif font before creating the form’s components. This affects the Java application, not the website’s CSS.

        JPanel panel=new JPanel(new BorderLayout(12,12));panel.setBorder(BorderFactory.createEmptyBorder(20,20,20,20));
        JLabel heading=new JLabel(title);heading.setFont(new Font(Font.SANS_SERIF,Font.BOLD,24));panel.add(heading,BorderLayout.NORTH);return panel;
    }

BorderLayout places the heading in NORTH and leaves CENTER for each experiment’s form. The empty border adds padding; the heading uses a larger bold font. Return the JPanel for further assembly.

    static void show(String title,JPanel panel) {
        JFrame frame=new JFrame(title);frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);frame.setContentPane(panel);frame.pack();frame.setLocationRelativeTo(null);frame.setVisible(true);
    }

show creates a JFrame, installs its content, packs it to component sizes, centres it and makes it visible. EXIT_ON_CLOSE ends this demonstration application when its window closes. The desktop main calls this helper on the event-dispatch thread.

    static int divide(String a,String b){return Integer.parseInt(a.trim())/Integer.parseInt(b.trim());}

Trim each field and use Integer.parseInt, then integer division. Invalid or out-of-int-range text throws NumberFormatException; a zero divisor throws ArithmeticException. An ordinary result such as 7/2 is 3.

    // The flag is used by off-screen tests; normal main always enables dialogs.
    public static JPanel createPanel(){return createPanel(true);}
    static JPanel createPanel(boolean dialogs){

The public no-argument createPanel calls createPanel(true). The boolean overload can suppress modal error dialogs for off-screen tests while leaving computation and field updates in the same listener.

        JPanel panel=root("Integer Division"),form=new JPanel(new GridLayout(0,2,10,12));
        JTextField first=new JTextField(20),second=new JTextField(20),result=new JTextField(20);first.setName("num1");second.setName("num2");result.setName("result");result.setEditable(false);
        form.add(new JLabel("Num1"));form.add(first);form.add(new JLabel("Num2"));form.add(second);form.add(new JLabel("Result"));form.add(result);panel.add(form,BorderLayout.CENTER);
        JButton button=new JButton("Divide");panel.add(button,BorderLayout.SOUTH);

Create labelled Num1/Num2 fields, a named result field and Divide. result.setEditable(false) prevents manual edits but permits updates by the program.

        button.addActionListener(e->{
            try{result.setText(Integer.toString(divide(first.getText(),second.getText())));}

The lambda reads current field text, calls divide and writes its successful integer result. Creating the listener itself does not perform the division.

            catch(NumberFormatException error){result.setText("");if(dialogs)JOptionPane.showMessageDialog(panel,"NumberFormatException: enter valid 32-bit integers.","Invalid input",JOptionPane.ERROR_MESSAGE);}
            catch(ArithmeticException error){result.setText("");if(dialogs)JOptionPane.showMessageDialog(panel,"ArithmeticException: division by zero.","Division error",JOptionPane.ERROR_MESSAGE);}

Both error paths clear old output. Show the appropriate JOptionPane only when dialogs is true. Catch order keeps the two different causes and their messages clear.

        });return panel;
    }

The callback closes, then createPanel returns the assembled UI. Later button clicks use the captured field references.

    public static void main(String[] args){SwingUtilities.invokeLater(()->show("Integer Division",createPanel()));}

}

SwingUtilities.invokeLater schedules the lambda on Swing’s event-dispatch thread. The lambda creates the panel and calls show. This main needs a graphical desktop; the panel and its event handlers are separate from console input.