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POProblems calling a method from another Java class
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  1. POProblems calling a method from another Java class
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    copied!<p>I am having a runtime error that states Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException at Status.copyState(Status.java:29) This is a class that is call the an instance of the Status calls (st): Main class is:</p> <pre><code>import javax.swing.*; import java.awt.event.*; import java.awt.*; /** * * * @author (Jason Sizemore) * @version (11-20-09 HW09) */ public class BetterCalculator extends Calculator { //attributes private JButton undo; private String undoText; private Status st; public BetterCalculator() { super(); st = new Status(); } public void createUserInterface3() { createUserInterface2(); undo = new JButton("undo"); jPanel.add(undo); undo.setBackground(Color.red); undo.setToolTipText("This is the undo feature"); undo.addActionListener(this); } public void actionPerformed(ActionEvent e) { super.actionPerformed(e); while(displayBox.getText() != null) { st.copyState(); } if(e.getSource() == undo) { Status st; st = new Status(); undoText = st.returnState(); displayBox.setText(undoText); } } public static void main(String[] args) { BetterCalculator myCalc; myCalc = new BetterCalculator(); myCalc.createUserInterface3(); } } </code></pre> <p>It is call the an instance of Status (st) Here is the Status class</p> <pre><code>import java.util.*; import java.awt.event.*; import java.awt.*; /** * Write a description of class Status here. * * @author (Jason Sizemore ) * @version (HW09 11-21-09) * This is a class to get the status for the undo feature */ public class Status extends BasicCalculator { //attributes private ArrayList&lt;String&gt; lastState; public String ls; public String rls; //constructors public Status() { lastState = new ArrayList&lt;String&gt;(10); } //Methods public void copyState() { //operand1 = Double.parseDouble(displayBox.getText()); ls = displayBox.getText(); lastState.add(ls); } public String returnState() { int sizeOfArrayList; sizeOfArrayList = lastState.size(); rls = lastState.get(sizeOfArrayList); return rls; } } </code></pre> <p>I know the issue is with the line ls = displayBox.getText(); I have a object take the return of a method on a object. what am I missing here.</p> <p>Thanks for any help.</p>
 

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