Java GUI - Mortgage Calculator

I am taking Java II programming and I have an assignment to write a mortgage calculator program with a GUI, that takes a users input, principal, term, and interest and then calculate the monthly payment after the user enters this input and clicks calculate. My program compiles but when I go to run it I get nothing just a lot of "garbage" in command prompt, which I cannot interpret. Could someone please review my code and tell me whats happening?

F.Y.I - As of right now, I only want the user to input a principal and then click on the calculate button, which then will trigger the event to have the principal mulitplied by 10 and then display the result. I only did this to try and start small and then add the rest (interest, term) later once I got this part to work.

import javax.swing.*;
 
//package learn;
 
public class MortgageCalGUI extends javax.swing.JFrame
{
 
	/** Creating a new form MortgageCalGUI **/
	public MortgageCalGUI()
	{
		//call to method Components() to initilize the new from
		Components();
		
	}
 
	/** The Components() method is called within our MortgageCalGUI constructor to initilize our new MortgageCalGUI form **/
	private void Components()
	{
		//creating text fields
		txtfld_principal = new javax.swing.JTextField();
 
		//creating labels for our text fields
		label_principal = new javax.swing.JLabel();
		label_principal.setText("Principal");
 
		label_monthly = new javax.swing.JLabel();
		label_monthly.setText("0");
		
 
		//creating Button
		btn_calculate = new javax.swing.JButton();
		btn_calculate.setText("Calculate");
 
		//event handler for our button btn_calculate
		btn_calculate.addActionListener(new java.awt.event.ActionListener() {
			public void actionPerformed(java.awt.event.ActionEvent evt) {
				CalculationPerformed(evt);
			}
		});		
		
		//create our "escape" route
		setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
		
		//create a new frame nameing it Mortgage Calculator
		JFrame frame = new JFrame("MortgageCalculator");
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		
		//set the layout of the window
		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)
					.addGroup(layout.createSequentialGroup()
						.addComponent(txtfld_principal, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
						.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
						.addComponent(label_principal))
					.addGroup(layout.createSequentialGroup()
						.addComponent(btn_calculate)	
						.addComponent(label_monthly)))
				.addContainerGap(27,Short.MAX_VALUE))
		);
		
		layout.linkSize(javax.swing.SwingConstants.HORIZONTAL, new java.awt.Component[] { btn_calculate, txtfld_principal, txtfld_interest, txtfld_term });
 
		
		layout.setVerticalGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
			.addGroup(layout.createSequentialGroup()
				.addContainerGap()
				.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
					.addComponent(txtfld_principal, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
					.addComponent(label_principal))
				.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
					.addComponent(btn_calculate)
					.addComponent(label_monthly))
				.addContainerGap(21, Short.MAX_VALUE))
		);
		pack();
	}
	
	private void CalculationPerformed(java.awt.event.ActionEvent evt)
	{
		double principal = (int)(Double.parseDouble(txtfld_principal.getText()));
 
		final double mthly = (principal * 10);
		label_monthly.setText(mthly + " Monthly Payment.");
	}	
 
	public static void main(String[] args)
	{
		java.awt.EventQueue.invokeLater(new Runnable() {
			public void run() {
				new MortgageCalGUI().setVisible(true);
			}
		});
	}
 
	//Variable Declarations
	private javax.swing.JLabel label_principal;
	private javax.swing.JLabel label_interest;
	private javax.swing.JLabel label_term;
	private javax.swing.JLabel label_monthly;
 
	private javax.swing.JTextField txtfld_principal;
	private javax.swing.JTextField txtfld_interest;
	private javax.swing.JTextField txtfld_term;
 
	private javax.swing.JButton btn_calculate;
}

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