Question

Can someone modify my code so that I do not get this error:

Exception in thread "main" java.lang.NullPointerException

at java.awt.Container.addImpl(Container.java:1043)

at java.awt.Container.add(Container.java:363)

at RatePanel.<init>(RatePanel.java:64)

at CurrencyConverter.main(CurrencyConverter.java:16)

This code should get the amount of money in US dollars from user and then let them select which currency they are trying to convert to and then in the textfield print the amount

//*********************************************************************
//File name: RatePanel.java
//Name: Brittany Hines
//Purpose: Panel for a program that convers different currencyNamerencies to use dollars
//*********************************************************************

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

public class RatePanel extends JPanel
{
private JComboBox currencyCombo;

private double[] rate; // exchange rates
private String[] currencyName;
private JLabel result;
private JTextField t1, t2;
private JButton b1;

// ------------------------------------------------------------
// Sets up a panel to convert cost from one of 6 currencies
// into U.S. Dollars. The panel contains a heading, a text
// field for the cost of the item, a combo box for selecting
// the currency, and a label to display the result.
// ------------------------------------------------------------
public RatePanel ()
{
JLabel title = new JLabel ("How much is that in dollars?");
title.setAlignmentX (Component.CENTER_ALIGNMENT);
title.setFont (new Font ("Helvetica", Font.BOLD, 20));

// Set up the arrays for the currency conversions
currencyName = new String[] {"Select the currency..",
"European Euro", "Canadian Dollar",
"Japanese Yen", "Australian Dollar",
"Indian Rupee", "Mexican Peso"};
rate = new double [] {0.0, 0.948968, 0.646920,
0.00803616, 0.562082,
0.0204441, 0.103735};


currencyCombo =new JComboBox(currencyName);

t2=new JTextField(20);
b1=new JButton("Convert");

t1=new JTextField(20);


add (title);
add (t2);
add (currencyCombo);
add (b1);


add (t1);



add (result);

result = new JLabel (Double.parseDouble(t2.getText()) * rate[currencyCombo.getSelectedIndex()] + "US Dollars");
t1.setText("Result: "+(String.format("%.2f", result)));

}


// ******************************************************
// Represents an action listener for the combo box.
// ******************************************************
private class ComboListener implements ActionListener
{
// --------------------------------------------------
// Determines which currency has been selected and
// the value in that currency then computes and
// displays the value in U.S. Dollars.
// --------------------------------------------------

public void actionPerformed (ActionEvent event)
{
int index = 0;
result.setText ("1 " + currencyName[index] +
" = " + rate[index] + " U.S. Dollars");
}


}
}

// **********************************************************************
// File name: CurrencyConverter.java
// Name:
// Purpose: Computes the dollar value of the cost of an item in another currency
// **********************************************************************
//
import java.awt.*;
import javax.swing.*;
public class CurrencyConverter
{
public static void main(String[] args)
{
JFrame frame = new JFrame("Currency Converter");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  
RatePanel ratePanel = new RatePanel();
frame.getContentPane().add(ratePanel);
frame.pack();
frame.setVisible(true);
  
}
}