Solutions to Self-Study Exercises

[Page 188]

Solution 4.1

The following modification of the GreeterApp class is an implementation of the High-Low Game:

public class HighLowApp { private KeyboardReader reader;   private int secretNumber;   public HighLowApp()   { reader = new KeyboardReader();     secretNumber = 1 + (int)(Math.random() * 100);   } // HighLowApp() constructor   public void run()   { int userGuess = -1;     reader.display("Guess my secret number between 1 and 100.");     while (userGuess != secretNumber)     {   reader.prompt("Please input your guess here > ");       userGuess = reader.getKeyboardInteger();       if (userGuess > secretNumber)         reader.display("Your guess was too high.");       if (userGuess < secretNumber)         reader.display("Your guess was too low.");     } // while     reader.display("Congratulations. Your guess was correct.");   } // run()   public static void main(String args[])   { HighLowApp app = new HighLowApp();     app.run();   } // main() } // HighLowApp class 

Solution 4.2

The following modification of GreeterGUI eliminates the JButton.

import javax.swing.*; import java.awt.*; import java.awt.event.*; public class GreeterGUI2 extends JFrame implements ActionListener { private JTextArea display;   private JTextField inField;   private Greeter greeter;   public GreeterGUI2(String title)   {   greeter = new Greeter();       buildGUI();       setTitle(title);       pack();       setVisible(true);   } // GreeterGUI2() 
[Page 189]  private void buildGUI()   {   Container contentPane = getContentPane();       contentPane.setLayout(new BorderLayout());       display = new JTextArea(10,30);       inField = new JTextField(10);       inField.addActionListener(this);       JPanel inputPanel = new JPanel();       inputPanel.add(new               JLabel("Input your name and type enter: "));       inputPanel.add(inField);       contentPane.add("Center", display);       contentPane.add("South", inputPanel);   } // buildGUI()   public void actionPerformed(ActionEvent e)   {   if (e.getSource() == inField)       {   String name = inField.getText();           display.append(greeter.greet(name) + "\n");       }   } // actionPerformed() } // GreeterGUI2 class 

Solution 4.3

Java code that prints out the sum of the squares of a set of integers read from a file named "numbers.txt":

import java.io.*; import java.util.Scanner; public class NumberFileReader {   private Scanner fileScan;                         // For file input     public NumberFileReader(String fName)     {   try         {   File theFile = new File(fName);             fileScan = new Scanner(theFile);         } catch (IOException e)         {    e.printStackTrace();         } // catch()     } // NumberFileReader()     public void readNumbers()     {   int num = 0;                                 // To store integers read         int num = 0:                                 // To store sum of squares         while (fileScan.hasNextInt())         {   num = fileScan.nextInt();             sum = sum + num * num;         } // while         System.out.println("The sum of squares = " + sum);     } // readNumbers()     public static void main(String[] args)     {   NumberFileReader nfr =             new NumberFileReader("numbers.txt");         nfr.readNumbers()     }  // main() } // NumberFileReader