Adding Buttons to StyleOptions.java

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Mervyn Singleton
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1 Adding Buttons to StyleOptions.java The files StyleOptions.java and StyleOptionsPanel.java are from Listings 5.14 and 5.15 of the text (with a couple of slight changes an instance variable fontsize is used rather than the literal 36 for font size and the variable style is an instance variable rather than local to the itemstatechanged method). The program demonstrates checkboxes and ItemListeners. In this exercise you will add a set of three radio buttons to let the user choose among three font sizes. The method of adding the radio buttons will be very similar to that in the QuoteOptionsPanel class (Listing 5.17 of the text). Before modifying the program compile and run the current version to see how it works and study the QuoteOptionsPanel example. Do the following to add the radio buttons to the panel: 1. Declare three objects small, medium, and large of type JRadioButton. 2. Instantiate the button objects labeling them Small Font, Medium Font, Large Font. Initialize the large font button to true. Set the background color of the buttons to cyan. 3. Instantiate a button group object and add the buttons to it. 4. Radio buttons produce action events so you need an ActionListener to listen for radio button clicks. The code you need to add to actionperformed will be similar to that in the QuoteListener in Listing In this case you need to set the fontsize variable (use 12 for small, 24 for medium, and 36 for large) in the if statement, then call the setfont method to set the font for the saying object. (Note: Instead of adding an ActionListener you could use the current ItemListener and add code to check to see if the source of the event was a radio button.) 5. In StyleOptionsPanel() add the ItemListener object to each button and add each button to the panel. 6. Compile and run the program. Note that as the font size changes the checkboxes and buttons re-arrange themselves in the panel. You will learn how to control layout later in the course. ******************************************************************** StyleOptions.java Author: Lewis/Loftus Demonstrates the use of check boxes. ******************************************************************** import javax.swing.jframe; public class StyleOptions Creates and presents the program frame public static void main (String[] args) JFrame frame = new JFrame ("Style Options"); frame.setdefaultcloseoperation (JFrame.EXIT_ON_CLOSE); StyleOptionsPanel panel = new StyleOptionsPanel(); frame.getcontentpane().add (panel); frame.pack(); frame.setvisible(true); Chapter 5: Conditionals and Loops 81

2 ************************************************************ StyleOptionsPanel.java Author: Lewis/Loftus Demonstrates the use of check boxes. ************************************************************ import javax. swing. *; import java.awt.*; import java.awt.event.*; public class StyleOptionsPanel extends JPanel private int fontsize = 36; private int style = Font.PLAIN; private JLabel saying; private JCheckBox bold, italic; Sets up a panel with a label and some check boxes that control the style of the label's font public StyleOptionsPanel() saying = new JLabel ("Say it with style!"); saying.setfont (new Font ("Helvetica", style, fontsize)); bold = new JCheckBox ("Bold"); bold.setbackground (Color.cyan); italic = new JCheckBox ("Italic"); italic.setbackground (Color.cyan); StyleListener listener = new StyleListener (); bold.additemlistener (listener); italic.additemlistener (listener) ; add (saying); add (bold); add (italic); setbackground (Color.cyan); setpreferredsize (new Dimension(300, 100)); ************************************************************ Represents the listener for both check boxes. ************************************************************ private class StyleListener implements ItemListener Updates the style of the label font style public void itemstatechanged (ItemEvent event) style = Font.PLAIN; if (bold.isselected()) style = Font.BOLD; if (italic.isselected()) style += Font.ITALIC; 82 Chapter 5: Conditionals and Loops

3 saying.setfont (new Font ("Helvetica", style, fontsize)); Chapter 5: Conditionals and Loops 83

4 An Array of Radio Buttons File ColorOptions.java contains a program that will display a set of radio buttons that let the user change the background color of the GUI. The file ColorOptionsPanel.java contains the skeleton of the panel for this program. Open the files and study the code that is already there. You will note that in ColorOptionsPanel.java there is an array color containing 5 colors already defined. Your task is to add an array of radio buttons so that a click of a radio button will cause the background of the panel to change to the corresponding color in the color array. 1. Define colorbutton to be an array of NUM_COLORS objects of type JRadioButton. 2. Instantiate each colorbutton with the appropriate color as the label (for example, the first button should be labeled Yellow ). The first button (corresponding to yellow) should be on (true) initially. 3. Recall that radio buttons must be grouped and that the selection of a radio button produces an action event. Hence you must have a ButtonGroup object and an ActionListener. Note that the skeleton of an ActionListener named ColorListener is already provided. So, you need to: a. Instantiate a ButtonGroup object and a ColorListener object. Comments in the code indicate where to do this. b. Each radio button needs to be added to your ButtonGroup object, the background color needs to be set (use white), your ColorListener needs to be added, and the button needs to be added to the panel. All of these can be done using a single for loop. So, add a for loop that goes through the radio buttons adding each to your ButtonGroup object, setting the background of each to white, adding your ColorListener to each, and adding each to the panel. 4. Fill in the body of the actionperformed method. This method needs to go through the buttons to determine which is selected and then set the background color accordingly. A simple for loop can do this. Use the isselected method to determine if a button is selected (for example, if (colorbutton[i].isselected())...). Use the color array to set the background color. 5. Test your program! ******************************************************************** ColorOptions.java Uses an array of radio buttons to change the background color. ******************************************************************** import javax.swing.*; public class ColorOptions Creates and presents the frame for the color change panel public static void main (String[] args) JFrame colorframe = new JFrame ("Color Options"); colorframe.setdefaultcloseoperation (JFrame.EXIT_ON_CLOSE); ColorOptionsPanel panel = new ColorOptionsPanel(); colorframe.getcontentpane().add (panel); colorframe.pack(); colorframe.setvisible(true); Chapter 8: Arrays 141

5 *********************************************************************** ColorOptionsPanel.java Represents the user interface for the ColorOptions program that lets the user change background color by selecting a radio button. *********************************************************************** import javax.swing.*; import java.awt.*; import java.awt.event.*; public class ColorOptionsPanel extends JPanel private final int WIDTH = 350, HEIGHT = 100, FONT_SIZE = 20; private final int NUM_COLORS = 5; private Color [] color = new Color[NUM_COLORS]; private JLabel heading; Sets up a panel with a label at the top and a set of radio buttons that control the background color of the panel public ColorOptionsPanel () Set up heading and colors heading = new JLabel ("Choose the background color!"); heading.setfont (new Font ("Helvetica", Font.BOLD, FONT_SIZE)); color[0] = Color.yellow; color[1] = Color.cyan; color[2] = Color.red; color[3] = Color.green; color[4] = Color.magenta; Instantiate a ButtonGroup object and a ColorListener object Set up the panel add (heading); setbackground (Color.yellow); setpreferredsize (new Dimension (WIDTH, HEIGHT)); Group the radio buttons, add a ColorListener to each, set the background color of each and add each to the panel. *************************************************************** Represents the listener for the radio buttons. *************************************************************** private class ColorListener implements ActionListener Updates the background color of the panel based on which radio button is selected public void actionperformed (ActionEvent event) Chapter 8: Arrays 142

Array indexing. Before we use an array, we have to declare it. For example, int[] height=new int[11];

Array indexing. Before we use an array, we have to declare it. For example, int[] height=new int[11]; Chapter 6 Arrays We want to organize objects or primitive data in a form that is easy to access and modify data. We will explore more about the ways to group and organize data in a later chapter, and even