Write an application that displays a solid square com- posed of a character input by the user (Fig. 12.29). The user also should input the size of the side of the square.

Question

a) Copying the template to your working directory. Copy the C:Examples Tutorial12ExercisesDisplaySquare directory to your C:SimplyJava direc- tory.

b) Opening the template file. Open the DisplaySquare.java file in your text editor.

c) Adding a method to your application that displays a square of characters. On line

141, add a comment indicating that the method will display a square in a JTextArea. On line 142, add the method header for this method. The method will be called dis- playSquare. This method contains two parameters–the first, of type int, should be called size, the second, of type String, should be called character. This method does not return a value, but simply performs a task (displaying a square). For such methods, the return type is specified as void. Specify the return type for display- Square as void. On line 143, add a left brace to begin the body of the method. On line 145, add the right brace to end the body of the method. Follow the brace with a comment i

Answer 1

```
1 // DisplaySquare.java
2 // Displays a square of characters where the size of the square
3 // and the characters used in the square are specified by the user.
4 import java.awt.*;
5 import java.awt.event.*;
6 import java.text.*;
7 import javax.swing.*;
8
9 public class DisplaySquare extends JFrame
10 {
11 // JLabel and JTextField for size of square sides
12 private JLabel squareSizeJLabel;
13 private JTextField squareSizeJTextField;
14
15 // JLabel and JTextField for fill character
16 private JLabel fillCharacterJLabel;
17 private JTextField fillCharacterJTextField;
18
19 // JTextArea and JScrollPane for displaying square
20 private JTextArea outputJTextArea;
21 private JScrollPane outputJScrollPane;
22
23 // JButton initiates creation and display of square
24 private JButton displaySquareJButton;
25
26 // no-argument constructor
27 public DisplaySquare()
28 {
29 createUserInterface();
30 }
31
32 // create and position GUI components; register event handlers
33 private void createUserInterface()
34 {
35 // get content pane for attaching GUI components
36 Container contentPane = getContentPane();
37
38 // enable explicit positioning of GUI components
39 contentPane.setLayout( null );
40
41 // set up squareSizeJLabel
42 squareSizeJLabel = new JLabel();
43 squareSizeJLabel.setBounds( 16, 16, 80, 21 );
44 squareSizeJLabel.setText( "Square size:" );
45 contentPane.add( squareSizeJLabel );
46
47 // set up squareSizeJTextField
48 squareSizeJTextField = new JTextField();
49 squareSizeJTextField.setBounds( 104, 16, 24, 21 );
50 squareSizeJTextField.setHorizontalAlignment(
51 JTextField.RIGHT );
52 contentPane.add( squareSizeJTextField );
53
54 // set up fillCharacterJLabel
55 fillCharacterJLabel = new JLabel();
56 fillCharacterJLabel.setBounds( 16, 56, 80, 21 );
57 fillCharacterJLabel.setText( "Fill character:" );
58 contentPane.add( fillCharacterJLabel );
59
60 // set up fillCharacterJTextField
61 fillCharacterJTextField = new JTextField();
62 fillCharacterJTextField.setBounds( 104, 56, 24, 21 );
63 fillCharacterJTextField.setHorizontalAlignment(
64 JTextField.RIGHT );
65 contentPane.add( fillCharacterJTextField );
66
67 // set up outputJTextArea
68 outputJTextArea = new JTextArea();
69 outputJTextArea.setBackground( Color.LIGHT_GRAY );
70 outputJTextArea.setEditable( false );
71 contentPane.add( outputJTextArea );
72
73 // set up outputJScrollPane
74 outputJScrollPane = new JScrollPane( outputJTextArea );
75 outputJScrollPane.setBounds( 16, 96, 248, 136 );
76 contentPane.add( outputJScrollPane );
77
78 // set up displaySquareJButton
79 displaySquareJButton = new JButton();
80 displaySquareJButton.setBounds( 144, 16, 120, 23 );
81 displaySquareJButton.setText( "Display Square" );
82 contentPane.add( displaySquareJButton );
83 displaySquareJButton.addActionListener(
84
85 new ActionListener() // anonymous inner class
86 {
87 // event handler called when
88 // displaySquareJButton is clicked
89 public void actionPerformed( ActionEvent event )
90 {
91 displaySquareJButtonActionPerformed( event );
92 }
93
94 } // end anonymous inner class
95
96 ); // end call to addActionListener
97
98 // set properties of application's window
99 setTitle( "Display Square" ); // set title bar string
100 setSize( 288, 276 ); // set window size
101 setVisible( true ); // display window
102
103 } // end method createUserInterface
104
105 // display a square of characters
106 private void displaySquareJButtonActionPerformed(
107 ActionEvent event )
108 {
109 // if valid input is entered
110 if ( ( squareSizeJTextField.getText() != "" ) &&
111 ( fillCharacterJTextField.getText() != "" ) )
112 {
113 // retrieve user input
114 int squareSize = Integer.parseInt(
115 squareSizeJTextField.getText() );
116 String fillCharacter = fillCharacterJTextField.getText();
117
118 displaySquare( squareSize, fillCharacter );
119 }

displaySquare( squareSize, fillCharacter );
120 else
121 {
122 JOptionPane.showMessageDialog( null,
123 "Square size and fill character needed",
124 "Incorrect Input", JOptionPane.ERROR_MESSAGE );
125 }
126
127 } // end method displaySquareJButtonActionPerformed
128
129 // display square in outputJTextArea
130 private void displaySquare( int size, String character )
131 {
132 outputJTextArea.setText( "" ); // clear output
133
134 // loop until row reaches value of first argument (size)
135 for ( int row = 1; row <= size; row++ )
136 {
137 // loop until column reaches value of size
138 for ( int column = 1; column <= size; column++ )
139 {
140 outputJTextArea.append( character );
141 }
142
143 outputJTextArea.append( "\n" ); // add line to output
144 }
145
146 } // end method displaySquare
147
148 // main method
149 public static void main( String[] args )
150 {
151 DisplaySquare application = new DisplaySquare();
152 application.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
153
154 } // end method main
155
156 } // end class DisplaySquare
```