Describe how you would change this code to overcome some of its shortcomings: /*

ID: 663974 • Letter: D

Question

Describe how you would change this code to overcome some of its shortcomings:

Topic: A basic Java Swing Calculator

Conventions Used in Source code
---------------------------------
   1. All JLabel components start with jlb*
   2. All JPanel components start with jpl*
   3. All JMenu components start with jmenu*
   4. All JMenuItem components start with jmenuItem*
   5. All JDialog components start with jdlg*
   6. All JButton components start with jbn*
*/

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.KeyStroke;

public class Calculator extends JFrame implements ActionListener{
   // Variables
   final int MAX_INPUT_LENGTH = 20;
   final int INPUT_MODE = 0;
   final int RESULT_MODE = 1;
   final int ERROR_MODE = 2;
   int displayMode;

   boolean clearOnNextDigit, percent;
   double lastNumber;
   String lastOperator;

   private JMenu jmenuFile, jmenuHelp;
   private JMenuItem jmenuitemExit, jmenuitemAbout;

   private JLabel jlbOutput;
   private JButton jbnButtons[];
   private JPanel jplMaster, jplBackSpace, jplControl;

   /*
   * Font(String name, int style, int size)
Creates a new Font from the specified name, style and point size.
   */

   Font f12 = new Font("Times New Roman", 0, 12);
   Font f121 = new Font("Times New Roman", 1, 12);

   // Constructor
   public Calculator()
   {
       /* Set Up the JMenuBar.
       * Have Provided All JMenu's with Mnemonics
       * Have Provided some JMenuItem components with Keyboard Accelerators
       */

       jmenuFile = new JMenu("File");
       jmenuFile.setFont(f121);
       jmenuFile.setMnemonic(KeyEvent.VK_F);

       jmenuitemExit = new JMenuItem("Exit");
       jmenuitemExit.setFont(f12);
       jmenuitemExit.setAccelerator(KeyStroke.getKeyStroke( KeyEvent.VK_X,
                                                   ActionEvent.CTRL_MASK));
       jmenuFile.add(jmenuitemExit);

       jmenuHelp = new JMenu("Help");
       jmenuHelp.setFont(f121);
       jmenuHelp.setMnemonic(KeyEvent.VK_H);

       jmenuitemAbout = new JMenuItem("About Calculator");
       jmenuitemAbout.setFont(f12);
       jmenuHelp.add(jmenuitemAbout);

       JMenuBar mb = new JMenuBar();
       mb.add(jmenuFile);
       mb.add(jmenuHelp);
       setJMenuBar(mb);

       //Set frame layout manager

setBackground(Color.gray);

jplMaster = new JPanel();

       jlbOutput = new JLabel("0");
       jlbOutput.setHorizontalTextPosition(JLabel.RIGHT);
       jlbOutput.setBackground(Color.WHITE);
       jlbOutput.setOpaque(true);

       // Add components to frame
       getContentPane().add(jlbOutput, BorderLayout.NORTH);

jbnButtons = new JButton[23];
// GridLayout(int rows, int cols, int hgap, int vgap)

JPanel jplButtons = new JPanel(); // container for Jbuttons

       // Create numeric Jbuttons
       for (int i=0; i<=9; i++)
       {
           // set each Jbutton label to the value of index
           jbnButtons[i] = new JButton(String.valueOf(i));
       }

       // Create operator Jbuttons
       jbnButtons[10] = new JButton("+/-");
       jbnButtons[11] = new JButton(".");
       jbnButtons[12] = new JButton("=");
       jbnButtons[13] = new JButton("/");
       jbnButtons[14] = new JButton("*");
       jbnButtons[15] = new JButton("-");
       jbnButtons[16] = new JButton("+");
       jbnButtons[17] = new JButton("sqrt");
       jbnButtons[18] = new JButton("1/x");
       jbnButtons[19] = new JButton("%");

       jplBackSpace = new JPanel();
       jplBackSpace.setLayout(new GridLayout(1, 1, 2, 2));

jbnButtons[20] = new JButton("Backspace");
jplBackSpace.add(jbnButtons[20]);

jplControl = new JPanel();
jplControl.setLayout(new GridLayout(1, 2, 2 ,2));

jbnButtons[21] = new JButton(" CE ");
jbnButtons[22] = new JButton("C");

jplControl.add(jbnButtons[21]);
jplControl.add(jbnButtons[22]);

//       Setting all Numbered JButton's to Blue. The rest to Red
       for (int i=0; i<jbnButtons.length; i++)   {
           jbnButtons[i].setFont(f12);

           if (i<10)
               jbnButtons[i].setForeground(Color.blue);

           else
               jbnButtons[i].setForeground(Color.red);
       }

       // Set panel layout manager for a 4 by 5 grid
       jplButtons.setLayout(new GridLayout(4, 5, 2, 2));

       //Add buttons to keypad panel starting at top left
       // First row
       for(int i=7; i<=9; i++)       {
           jplButtons.add(jbnButtons[i]);
       }

       // add button / and sqrt
       jplButtons.add(jbnButtons[13]);
       jplButtons.add(jbnButtons[17]);

       // Second row
       for(int i=4; i<=6; i++)
       {
           jplButtons.add(jbnButtons[i]);
       }

       // add button * and x^2
       jplButtons.add(jbnButtons[14]);
       jplButtons.add(jbnButtons[18]);

       // Third row
       for( int i=1; i<=3; i++)
       {
           jplButtons.add(jbnButtons[i]);
       }

       //adds button - and %
       jplButtons.add(jbnButtons[15]);
       jplButtons.add(jbnButtons[19]);

       //Fourth Row
       // add 0, +/-, ., +, and =
       jplButtons.add(jbnButtons[0]);
       jplButtons.add(jbnButtons[10]);
       jplButtons.add(jbnButtons[11]);
       jplButtons.add(jbnButtons[16]);
       jplButtons.add(jbnButtons[12]);

       jplMaster.setLayout(new BorderLayout());
       jplMaster.add(jplBackSpace, BorderLayout.WEST);
       jplMaster.add(jplControl, BorderLayout.EAST);
       jplMaster.add(jplButtons, BorderLayout.SOUTH);

       // Add components to frame
       getContentPane().add(jplMaster, BorderLayout.SOUTH);
       requestFocus();

       //activate ActionListener
       for (int i=0; i<jbnButtons.length; i++){
           jbnButtons[i].addActionListener(this);
       }

       jmenuitemAbout.addActionListener(this);
       jmenuitemExit.addActionListener(this);

clearAll();

//add WindowListener for closing frame and ending program
addWindowListener(new WindowAdapter() {

               public void windowClosed(WindowEvent e)
               {
                   System.exit(0);
               }
           }
       );
       this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   }   //End of Contructor Calculator

   // Perform action
   public void actionPerformed(ActionEvent e){
       double result = 0;

       if(e.getSource() == jmenuitemAbout){
           JDialog dlgAbout = new CustomABOUTDialog(this, "About Java Swing Calculator", true);
           dlgAbout.setVisible(true);
       }else if(e.getSource() == jmenuitemExit){
           System.exit(0);
       }

       // Search for the button pressed until end of array or key found
       for (int i=0; i<jbnButtons.length; i++)
       {
           if(e.getSource() == jbnButtons[i])
           {
               switch(i)
               {
                   case 0:
                       addDigitToDisplay(i);
                       break;

                   case 1:
                       addDigitToDisplay(i);
                       break;

                   case 2:
                       addDigitToDisplay(i);
                       break;

                   case 3:
                       addDigitToDisplay(i);
                       break;

                   case 4:
                       addDigitToDisplay(i);
                       break;

                   case 5:
                       addDigitToDisplay(i);
                       break;

                   case 6:
                       addDigitToDisplay(i);
                       break;

                   case 7:
                       addDigitToDisplay(i);
                       break;

                   case 8:
                       addDigitToDisplay(i);
                       break;

                   case 9:
                       addDigitToDisplay(i);
                       break;

                   case 10:   // +/-
                       processSignChange();
                       break;

                   case 11:   // decimal point
                       addDecimalPoint();
                       break;

                   case 12:   // =
                       processEquals();
                       break;

                   case 13:   // divide
                       processOperator("/");
                       break;

                   case 14:   // *
                       processOperator("*");
                       break;

                   case 15:   // -
                       processOperator("-");
                       break;

                   case 16:   // +
                       processOperator("+");
                       break;

                   case 17:   // sqrt
                       if (displayMode != ERROR_MODE)
                       {
                           try
                           {
                               if (getDisplayString().indexOf("-") == 0)
                                   displayError("Invalid input for function!");

                               result = Math.sqrt(getNumberInDisplay());
                               displayResult(result);
                           }

                           catch(Exception ex)
                           {
                               displayError("Invalid input for function!");
                               displayMode = ERROR_MODE;
                           }
                       }
                       break;

                   case 18:   // 1/x
                       if (displayMode != ERROR_MODE){
                           try
                           {
                               if (getNumberInDisplay() == 0)
                                   displayError("Cannot divide by zero!");

                               result = 1 / getNumberInDisplay();
                               displayResult(result);
                           }

                           catch(Exception ex)   {
                               displayError("Cannot divide by zero!");
                               displayMode = ERROR_MODE;
                           }
                       }
                       break;

                   case 19:   // %
                       if (displayMode != ERROR_MODE){
                           try   {
                               result = getNumberInDisplay() / 100;
                               displayResult(result);
                           }

                           catch(Exception ex)   {
                               displayError("Invalid input for function!");
                               displayMode = ERROR_MODE;
                           }
                       }
                       break;

                   case 20:   // backspace
                       if (displayMode != ERROR_MODE){
                           setDisplayString(getDisplayString().substring(0,
                                       getDisplayString().length() - 1));

                           if (getDisplayString().length() < 1)
                               setDisplayString("0");
                       }
                       break;

                   case 21:   // CE
                       clearExisting();
                       break;

                   case 22:   // C
                       clearAll();
                       break;
               }
           }
       }
   }

   void setDisplayString(String s){
       jlbOutput.setText(s);
   }

   String getDisplayString (){
       return jlbOutput.getText();
   }

   void addDigitToDisplay(int digit){
       if (clearOnNextDigit)
           setDisplayString("");

       String inputString = getDisplayString();

       if (inputString.indexOf("0") == 0){
           inputString = inputString.substring(1);
       }

       if ((!inputString.equals("0") || digit > 0) && inputString.length() < MAX_INPUT_LENGTH){
           setDisplayString(inputString + digit);
       }

       displayMode = INPUT_MODE;
       clearOnNextDigit = false;
   }

void addDecimalPoint(){
displayMode = INPUT_MODE;

if (clearOnNextDigit)
setDisplayString("");

       String inputString = getDisplayString();

       // If the input string already contains a decimal point, don't
       // do anything to it.
       if (inputString.indexOf(".") < 0)
           setDisplayString(new String(inputString + "."));
   }

   void processSignChange(){
       if (displayMode == INPUT_MODE)
       {
           String input = getDisplayString();

           if (input.length() > 0 && !input.equals("0"))
           {
               if (input.indexOf("-") == 0)
                   setDisplayString(input.substring(1));

               else
                   setDisplayString("-" + input);
           }

       }

       else if (displayMode == RESULT_MODE)
       {
           double numberInDisplay = getNumberInDisplay();

           if (numberInDisplay != 0)
               displayResult(-numberInDisplay);
       }
   }

   void clearAll()   {
       setDisplayString("0");
       lastOperator = "0";
       lastNumber = 0;
       displayMode = INPUT_MODE;
       clearOnNextDigit = true;
   }

   void clearExisting(){
       setDisplayString("0");
       clearOnNextDigit = true;
       displayMode = INPUT_MODE;
   }

   double getNumberInDisplay()   {
       String input = jlbOutput.getText();
       return Double.parseDouble(input);
   }

   void processOperator(String op) {
       if (displayMode != ERROR_MODE)
       {
           double numberInDisplay = getNumberInDisplay();

           if (!lastOperator.equals("0"))
           {
               try
               {
                   double result = processLastOperator();
                   displayResult(result);
                   lastNumber = result;
               }

               catch (DivideByZeroException e)
               {
               }
           }

           else
           {
               lastNumber = numberInDisplay;
           }

           clearOnNextDigit = true;
           lastOperator = op;
       }
   }

void processEquals(){
double result = 0;

       if (displayMode != ERROR_MODE){
           try
           {
               result = processLastOperator();
               displayResult(result);
           }

           catch (DivideByZeroException e)   {
               displayError("Cannot divide by zero!");
           }

           lastOperator = "0";
       }
   }

   double processLastOperator() throws DivideByZeroException {
       double result = 0;
       double numberInDisplay = getNumberInDisplay();

       if (lastOperator.equals("/"))
       {
           if (numberInDisplay == 0)
               throw (new DivideByZeroException());

           result = lastNumber / numberInDisplay;
       }

       if (lastOperator.equals("*"))
           result = lastNumber * numberInDisplay;

if (lastOperator.equals("-"))
result = lastNumber - numberInDisplay;

if (lastOperator.equals("+"))
result = lastNumber + numberInDisplay;

return result;
}

   void displayResult(double result){
       setDisplayString(Double.toString(result));
       lastNumber = result;
       displayMode = RESULT_MODE;
       clearOnNextDigit = true;
   }

   void displayError(String errorMessage){
       setDisplayString(errorMessage);
       lastNumber = 0;
       displayMode = ERROR_MODE;
       clearOnNextDigit = true;
   }

   public static void main(String args[]) {
       Calculator calci = new Calculator();
       Container contentPane = calci.getContentPane();
//       contentPane.setLayout(new BorderLayout());
       calci.setTitle("Java Swing Calculator");
       calci.setSize(241, 217);
       calci.pack();
       calci.setLocation(400, 250);
       calci.setVisible(true);
       calci.setResizable(false);
   }

}       //End of Swing Calculator Class.

class DivideByZeroException extends Exception{
   public DivideByZeroException()
   {
       super();
   }

   public DivideByZeroException(String s)
   {
       super(s);
   }
}

class CustomABOUTDialog extends JDialog implements ActionListener {
JButton jbnOk;

   CustomABOUTDialog(JFrame parent, String title, boolean modal){
       super(parent, title, modal);
       setBackground(Color.black);

       JPanel p1 = new JPanel(new FlowLayout(FlowLayout.CENTER));

       StringBuffer text = new StringBuffer();
       text.append("Calculator Information ");
       text.append("Developer:   Hemanth ");
       text.append("Version:   1.0");

       JTextArea jtAreaAbout = new JTextArea(5, 21);
       jtAreaAbout.setText(text.toString());
       jtAreaAbout.setFont(new Font("Times New Roman", 1, 13));
       jtAreaAbout.setEditable(false);

       p1.add(jtAreaAbout);
       p1.setBackground(Color.red);
       getContentPane().add(p1, BorderLayout.CENTER);

       JPanel p2 = new JPanel(new FlowLayout(FlowLayout.CENTER));
       jbnOk = new JButton(" OK ");
       jbnOk.addActionListener(this);

p2.add(jbnOk);
getContentPane().add(p2, BorderLayout.SOUTH);

setLocation(408, 270);
setResizable(false);

       addWindowListener(new WindowAdapter() {
               public void windowClosing(WindowEvent e)
               {
                   Window aboutDialog = e.getWindow();
                   aboutDialog.dispose();
               }
           }
       );

pack();
}

   public void actionPerformed(ActionEvent e)
   {
       if(e.getSource() == jbnOk)   {
           this.dispose();
       }
   }

}

Explanation / Answer

I have fixed few issues with developer tags and include functions.

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.*;

   boolean clearOnNextDigit, percent;
   double lastNumber;
   String lastOperator;

   private JMenu jmenuFile, jmenuHelp;
   private JMenuItem jmenuitemExit, jmenuitemAbout;

   private JLabel jlbOutput;
   private JButton jbnButtons[];
   private JPanel jplMaster, jplBackSpace, jplControl;

   /*
   * Font(String name, int style, int size)
      Creates a new Font from the specified name, style and point size.
   */

   Font f12 = new Font("Times New Roman", 0, 12);
   Font f121 = new Font("Times New Roman", 1, 12);

   // Constructor
   public Calculator()
   {
       /* Set Up the JMenuBar.
       * Have Provided All JMenu's with Mnemonics
       * Have Provided some JMenuItem components with Keyboard Accelerators
       */

       jmenuFile = new JMenu("File");
       jmenuFile.setFont(f121);
       jmenuFile.setMnemonic(KeyEvent.VK_F);

       jmenuitemExit = new JMenuItem("Exit");
       jmenuitemExit.setFont(f12);
       jmenuitemExit.setAccelerator(KeyStroke.getKeyStroke( KeyEvent.VK_X,
                                                   ActionEvent.CTRL_MASK));
       jmenuFile.add(jmenuitemExit);