I having this error in my Java code (using a widgetview class given by instructor) and was curious if anyone can help me fix this error I am having.

Error:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException

at StringAnalysis$2.actionPerformed(StringAnalysis.java:40)

Code:

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import javax.swing.*;

public class StringAnalysis {

static StringSet sSet;

public static void main(String[] args) {

//Create instance of WidgetView

WidgetView wv = new WidgetView();

//Create Labels, Fields, Buttons

JLabel sInput = new JLabel("Enter a String");

JButton submit = new JButton("Push to include String");

JTextField inputStr = new JTextField(10);

JLabel numStr = new JLabel("Number of Strings: 0");

JLabel numChar = new JLabel("Number of Characters: 0");

//Add to WidgetView

wv.add(sInput);

wv.add(inputStr);

wv.add(submit);

wv.add(numStr);

wv.add(numChar);

submit.addActionListener(new ActionListener() {

public void actionPerformed(ActionEvent e) {

sSet.addString(inputStr.getText());

inputStr.setText("");

numStr.setText("Number of Strings: " + sSet.getNumberofString());

numChar.setText("Number of Characters:" + sSet.getNumberOfChar());

}

});

inputStr.addActionListener(new ActionListener() {

public void actionPerformed(ActionEvent e) {

sSet.addString(inputStr.getText());

inputStr.setText("");

numStr.setText("Number of Strings: " + sSet.getNumberofString());

numChar.setText("Number of Characters:" + sSet.getNumberOfChar());

}

});

}

}