Chapter 3 Exercise Solutions

1
Chapter 3 Exercise Solutions

• Exercise 3.1 What output is produced by
  the following code fragment?
• String m1, m2, m3
• m1 "Quest for the Holy Grail"
• m2 m1.toLowerCase()
• m3 m1 " " m2
• System.out.println (m3.replace('h', 'z'))
• The output produced is
• Quest for tze Holy Grail quest for tze zoly
  grail
• The original string is concatenated with a
  lowercase version of itself, then all lowercase
  h characters are replaced with z.

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Chapter 3 Exercise Solutions

• Exercise 3.2Write an assignment statement that
  computes the square root of the sum of num1 and
  num2 and assigns the result to num3.
• num3 Math.sqrt(num1 num2)
• Exercise 3.3Write a single statement that
  computes and prints the absolute value of total.
• System.out.println (Math.abs(total))
• Exercise 3.4What is the effect of the following
  import statement?
• import java.awt.
• This statement allows all the classes in the
  java.awt package to be referenced in a program
  without the explicit package name.

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Chapter 3 Exercise Solutions

• Exercise 3.5Assuming that a Random object has
  been created called generator, what is the range
  of the result of each of the following
  expressions?
• generator.nextInt(20)
• 0 to 19, inclusive
• generator.nextInt(8) 1
• 1 to 8, incluslive
• generator.nextInt(45) 10
• 10 to 54, inclusive
• generator.nextInt(100) 50
• -50 to 49, inclusive

4
Chapter 3 Exercise Solutions

• Exercise 3.6Write code to declare and
  instantiate an object of the Random class (call
  the object reference variable rand). Then write a
  list of expressions using the nextInt method that
  generate random numbers in the following
  specified ranges, including the endpoints. Use
  the version of the nextInt method that accepts a
  single integer parameter.
• Random rand new Random()
• 0 to 10
• rand.nextInt(11)
• 0 to 500
• rand.nextInt(501)
• 1 to 10
• rand.nextInt(10) 1

1 to 500 rand.nextInt(500) 1 25 to
50 rand.nextInt(26) 25 10 to
15 rand.nextInt(26) 10
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Chapter 3 Exercise Solutions

• Exercise 3.7Write code statements to create a
  DecimalFormat object that will round a formatted
  value to 4 decimal places. Then write a statement
  that uses that object to print the value of
  result, properly formatted.
• DecimalFormat fmt new DecimalFormat
  (0.)
• System.out.println (fmt.format(result))

6
Chapter 3 Programming Project Solutions

• 3.3 Write an application that reads the lengths
  a,b,c of the sides of a triangle from the user.
  Compute the area of the triangle using Herons
  formula where s is one-half the perimeter of
  the triangle, i.e., s ½ (abc). Print the
  area to three decimal places.

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Chapter 3 Project Solutions Area of a Triangle

• import java.util.Scanner
• import java.text.DecimalFormat
• public class TriangleArea
• //----------------------------------------------
  -------------------------------// Computes the
  area of a triangle given the length of each//
  side. Uses Heron's formula.//--------------------
  --------------------------------------------------
  -------
• public static void main (String args)
• double side1, side2, side3, temp, temp2,
  area
• Scanner sc new Scanner(System.in)
• System.out.print ("Enter the length of side
  1 ")
• side1 Double.parseDouble(sc.nextLine())
• System.out.print ("Enter the length of side
  2 ")
• side2 sc.nextDouble()
• System.out.print ("Enter the length of side
  3 ")
• side3 Double.parseDouble(sc.nextLine())
• // Continued on next slide

8
Chapter 3 Project Solutions Area of a Triangle

• temp (side1 side2 side3) / 2 //
  compute s
• temp2 temp (temp-side1) (temp-side2)
  (temp-side3)
• area Math.sqrt (temp2)
• DecimalFormat fmt new DecimalFormat
  ("0.")
• System.out.println ("Area "
  fmt.format(area))

// TriangleArea.java continued
9
Chapter 3 Programming Project Solutions

• 3.5 Modify the LabelDemo program so that it
  displays a fourth label, with the text of the
  label centered above the image.
• import java.awt.
• import javax.swing.
• public class LabelDemo
• //---------------------------------------------
  --------------------
• // Creates and displays the primary
  application frame.
• //---------------------------------------------
  --------------------
• public static void main (String args)
• JFrame frame new JFrame ("Label Demo")
• frame.setDefaultCloseOperation
  (JFrame.EXIT_ON_CLOSE)
• ImageIcon icon new ImageIcon
  ("devil.gif")
• JLabel label1, label2, label3, label4

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Chapter 3 Project Solutions Add a Devil

• //---------------------------------------------
  -----------------------------
• // Display four labels with different
  text/icon orientations.
• //---------------------------------------------
  -----------------------------
• label1 new JLabel ("Devil Left", icon,
  SwingConstants.CENTER)
• label2 new JLabel ("Devil Right", icon,
  SwingConstants.CENTER)
• label2.setHorizontalTextPosition
  (SwingConstants.LEFT)
• label2.setVerticalTextPosition
  (SwingConstants.CENTER)
• label3 new JLabel ("Devil Above", icon,
  SwingConstants.CENTER)
• label3.setHorizontalTextPosition
  (SwingConstants.CENTER)
• label3.setVerticalTextPosition
  (SwingConstants.BOTTOM)
• label4 new JLabel ("Devil Below", icon,
  SwingConstants.LEFT)
• label4.setHorizontalTextPosition
  (SwingConstants.CENTER)
• label4.setVerticalTextPosition
  (SwingConstants.TOP)

// LabelPanel.java continued
11
Chapter 3 Project Solutions Add a Devil

• JPanel panel new JPanel()
• panel.setBackground (Color.cyan)
• panel.setPreferredSize (new Dimension (200,
  250))
• panel.add (label1)
• panel.add (label2)
• panel.add (label3)
• panel.add (label4)
• frame.getContentPane().add(panel)
• frame.pack()
• frame.setVisible(true)

// LabelPanel.java continued
12
Output of Modified LabelDemo Application