Thread: GUI Not Loading

I'm trying to make a basic GUI program that computes interest based on a few user-specified values.

When I run the driver without adding a listener to my buttons, everything works properly, but when I go to add the listener to the button, the GUI doesn't show when I run the driver.

Driver class:

package calculator;
 
import javax.swing.JFrame;
import javax.swing.WindowConstants;
 
 
public class InterestGUI {
 
	public static void createAndShowGUI() {
		JFrame frame = new JFrame("Interest Calculator");
		frame.setContentPane(new calcGUI());
		frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
		frame.pack();
		frame.setVisible(true);
	}
 
	public static void main(String[] args) {
		javax.swing.SwingUtilities.invokeLater(new Runnable() {
			public void run() {
				createAndShowGUI();
			}
		});
	}
}

GUI Class

package calculator;
 
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JButton;
import javax.swing.JTextField;
 
 
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.text.NumberFormat;
 
public class calcGUI extends JPanel{
 
    private JButton simpleInterestButton = new JButton("Compute Simple Interest");
    private JButton compoundInterestButton = new JButton("Compute Compound Interest");
    private JLabel principal = new JLabel("Principal:");
    private JLabel rate = new JLabel("Rate(Percentage):");
    private JLabel years = new JLabel("Years:");
    private JTextField principalInput = new JTextField(7);
    private JTextField rateInput = new JTextField(7);
    private JTextField yearsInput = new JTextField(7);
    private JLabel interestResult = new JLabel(interestTotal);
    private static String interestTotal;
    private JPanel topPanel = new JPanel();
    private JPanel midPanel = new JPanel();
    private JPanel bottomPanel = new JPanel();
 
	public class simpleInterestButtonListener implements ActionListener {
		private String principalValStr = principalInput.getText();
		private double principalValInt = Integer.parseInt(principalValStr.trim());
		private String rateValStr = rateInput.getText();
		private double rateValInt = Integer.parseInt(rateValStr.trim());
		private String yearsValStr = yearsInput.getText();
		private double yearsValInt = Integer.parseInt(yearsValStr.trim());
		private double simpleInterest = 0;
		private String simpleInterestStr = "";
 
		public void actionPerformed(ActionEvent arg0) {
			simpleInterest = principalValInt + (principalValInt*(rateValInt/100)*yearsValInt);
			simpleInterestStr = NumberFormat.getCurrencyInstance().format(simpleInterest);
			interestTotal = "Computed simple interest is " + simpleInterestStr;
		}
	}
 
	public calcGUI() {
		topPanel.add(principal);
		topPanel.add(principalInput);
		topPanel.add(rate);
		topPanel.add(rateInput);
		topPanel.add(years);
		topPanel.add(yearsInput);
		add(topPanel);
		simpleInterestButton.addActionListener(new simpleInterestButtonListener());
		midPanel.add(simpleInterestButton);
 
		compoundInterestButton.addActionListener(new ActionListener() {
			private String principalValStr = principalInput.getText();
			private double principalValInt = Integer.parseInt(principalValStr.trim());
			private String rateValStr = rateInput.getText();
			private double rateValInt = Integer.parseInt(rateValStr.trim());
			private String yearsValStr = yearsInput.getText();
			private double yearsValInt = Integer.parseInt(yearsValStr.trim());
			private double compoundInterest = 0;
			private String compoundInterestStr = "";
 
			public void actionPerformed(ActionEvent arg0) {
				compoundInterest = (int) (principalValInt*Math.pow((1+rateValInt/100),yearsValInt));
				compoundInterestStr = NumberFormat.getCurrencyInstance().format(compoundInterest);
				interestTotal = "Computed simple interest is " + compoundInterestStr;
			}
		});
		midPanel.add(compoundInterestButton);
		add(midPanel);
		bottomPanel.add(interestResult);
		add(bottomPanel);
	}
}

Originally Posted by ADAMWD

Also, how can I format it so that the buttons are below the text fields, and the interestResult label below the buttons, rather than everything being in a line.

Recommended reading: Lesson: Laying Out Components Within a Container (The Java™ Tutorials > Creating a GUI With JFC/Swing)