This assignment is designed to test your understanding of graphical user interface components and Event Driven programming in Java using Swing. You will write and attach event handlers to an existing graphical user interface (GUI) for an application that displays and manipulates a Color Model.

Java program is given below

Explanation:

JavaPadGUI.java

package javapad.gui;

import java.awt.BorderLayout;

import java.awt.Container;

import java.awt.Dimension;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import java.awt.event.WindowAdapter;

import java.awt.event.WindowEvent;

import java.io.File;

import java.io.FileNotFoundException;

import java.io.PrintWriter;

import java.util.Scanner;

import javax.swing.JButton;

import javax.swing.JFrame;

import javax.swing.JLabel;

import javax.swing.JOptionPane;

import javax.swing.JPanel;

import javax.swing.JScrollPane;

import javax.swing.JTextArea;

public class JavaPadGUI extends JFrame implements ActionListener{

  //constants

  private static final String TITLE = "Macrosoft JavaPad XP";

  private static final String SLOGAN = "Macrosoft: Resistance is futile";

  //button names

  private static final String NEW = "New";

  private static final String LOAD = "Load";

  private static final String SAVE = "Save";

  private static final String QUIT = "Quit";

  private static final String FILENAME = "hardcode.txt";

  //messages

  private static final String QUIT_MSG = "Quitting, Save?";

  private static final String LOAD_ERR = "Could not access file " + FILENAME;

  //fields

  private JTextArea txtContent;

  private JButton butNew, butLoad, butSave, butQuit;

  public JavaPadGUI()

  {

      super(TITLE);

      createUI();

      setSize(new Dimension(400, 300));

      setDefaultCloseOperation(EXIT_ON_CLOSE);

  }

  private void createUI()

  {

      Container c = getContentPane();

      c.setLayout(new BorderLayout(30,30));

      //create the buttons panel

      JPanel butPanel = new JPanel();

      butPanel.add(butNew = new JButton(NEW));

      butPanel.add(butLoad = new JButton(LOAD));

      butPanel.add(butSave = new JButton(SAVE));

      butPanel.add(butQuit = new JButton(QUIT));

      //set command names for the buttons, these will be when button is clicked

      butNew.setActionCommand(NEW);

      butLoad.setActionCommand(LOAD);

      butSave.setActionCommand(SAVE);

      butQuit.setActionCommand(QUIT);

      JPanel sloganPanel = new JPanel();

      sloganPanel.add(new JLabel(SLOGAN));

      //create textarea with scrollbar

      txtContent = new JTextArea(15, 25);

      txtContent.setLineWrap(true);

      JScrollPane scroll = new JScrollPane(txtContent);

      //now add all components

      c.add(butPanel, BorderLayout.NORTH);

      c.add(scroll, BorderLayout.CENTER);

      c.add(sloganPanel, BorderLayout.SOUTH);

      //set the actionlistner to buttons to handle button click event

      butNew.addActionListener(this);

      butLoad.addActionListener(this);

      butSave.addActionListener(this);

      butQuit.addActionListener(this);

  }

  public void actionPerformed(ActionEvent e)

  {

      String cmd = e.getActionCommand();

      if(cmd.equals(NEW))

          txtContent.setText("");

      else if (cmd.equals(LOAD))

          load();

      else if(cmd.equals(SAVE))

          save();

      else if (cmd.equals(QUIT))

          quit();

  }

  private void quit()

  {

      int option = JOptionPane.showConfirmDialog(this, QUIT_MSG);

      if(option == JOptionPane.YES_OPTION)

      {

          save();

      }

      System.exit(0);

  }

  private void save()

  {

      try {

          PrintWriter w = new PrintWriter(new File(FILENAME));

          w.write(txtContent.getText());

          w.close();

      } catch (FileNotFoundException e) {

          JOptionPane.showMessageDialog(this,"I/O Error", LOAD_ERR, JOptionPane.ERROR_MESSAGE);

      }

  }

  private void load()

  {

      try {

          Scanner s = new Scanner(new File(FILENAME));

          String str = "";

          while(s.hasNextLine())

              str += s.nextLine();

          txtContent.setText(str);

          s.close();

      } catch (FileNotFoundException e) {

          JOptionPane.showMessageDialog(this, LOAD_ERR, "I/O Error",JOptionPane.ERROR_MESSAGE);

      }

  }

}

RunJavaPad.java

package javapad;

import javapad.gui.JavaPadGUI;

public class RunJavaPad {

  public static void main(String[] args) {

      JavaPadGUI gui = new JavaPadGUI();

      gui.setVisible(true);

  }

}

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