Java Exercise Answers

Posted on By William Jojo
Java Book

(Updated August 26, 2020)

Table of contents

    Chapter 1
    Chapter 2
    Chapter 3
    Chapter 4
    Chapter 5
    Chapter 6
    Chapter 7a
    Chapter 7b
    Chapter 8
    Chapter 9
    Chapter 9s
    Chapter 10
    Chapter 11
    Chapter 12
    Chapter 13
    Chapter 14
    Chapter 15a
    Chapter 15b
    Chapter 16
    Chapter 17
    Chapter 18

Chapter 1

[Note: There are no specific answers to Chapter 1.]

Chapter 2

Exercise 1 solution

String name;

Exercise 2 solution

int i;
double d;
boolean b;

Exercise 3 solution

i = 35;
d = 3.14;
b = false;
System.out.println("i is " + i);
System.out.println("d is " + d);
System.out.println("b is " + b);

Alternative println with newlines

System.out.println("i is " + i + "\nd is " + d + "\nb is " + b);

Exercise 5 solution

Scanner kb = new Scanner(System.in);

System.out.print("Enter an integer: ");
i = kb.nextInt();
System.out.print("Enter a double: ");
d = kb.nextDouble();
System.out.print("Enter a boolean: ");
i = kb.nextBoolean();

Chapter 3

  1. (Beginner) Which package would you find the following classes:
    1. java.util
    2. java.io
    3. java.lang
    4. java.io
    5. javax.swing
    6. java.lang
    7. java.lang
    8. java.lang
  2. (Beginner) Which class would you find the following methods:
    1. Math
    2. String
    3. String
    4. Scanner
    5. Math
    6. JOptionPane
    7. String
    8. Scanner
    9. String
    10. PrintWriter
    11. PrintWriter
  3. (Intermediate) In your IDE, create some method calls as practice using:
    1. input = showInputDialog("Enter your name:");
    2. showMessageDialog(null, "Thank you!");
    3. choice = JOptionPane.showConfirmDialog(null, "Confirm quit?");
  4. (Intermediate) Write statements using Math.random() for the following ranges:
    1. (int)(Math.random() * 5 + 2);
    2. (int)(Math.random() * 7 + 3);
    3. (int)(Math.random() * 26 + 30);
    4. (int)(Math.random() * 7 +59);
  5. (Intermediate) Using the indexOf() String method, write statements to split the following strings into two parts: 
    1. int p;
String part1, part2, s = "Sally Mathers";

p = s.indexOf(" ");
part1 = s.substring(0,p);
part2 = s.substring(p+1);
    2. int p;
String part1, part2, s = "3d6";

p = s.indexOf("d");
part1 = s.substring(0,p);
part2 = s.substring(p+1);
    3. int p;
String part1, part2, s = "44*36";

p = s.indexOf("*");
part1 = s.substring(0,p);
part2 = s.substring(p+1);

Chapter 4

Exercise 1 solution

public class Ch4Ex1 {
  public static void main(String[] args) {
    
    // DC is 16, constitution modifier is 2.
    int dc = 16, roll, conmod = 2;
    
    roll = (int)(Math.random() * 20 + 1);
    
    System.out.println("DC = " + dc + ", roll = " + roll + ", mod = " + conmod);
    
    if ( roll + conmod >= dc )
      System.out.println("A sense of nausea comes over you and then immediately dissipates.");
    else {
      System.out.println("You feel very sick and extremely pain in your muscles.");
      System.out.println("You are now considered poisoned.");
    }
  }
}

Exercise 2 solution

public class Ch4Ex2 {
  public static void main(String[] args) {
    
    String sdow = "Tuesday";
    String ndow;
    
    switch ( sdow ) {
      case "Sunday" :
        ndow = 0;
        break;
      case "Monday" :
        ndow = 1;
        break;
      case "Tuesay" :
        ndow = 2;
        break;
      case "Wednesday" :
        ndow = 3;
        break;
      case "Thursday" :
        ndow = 4;
        break;
      case "Friday" :
        ndow = 5;
        break;
      case "Saturday" :
        ndow = 6;
        break;
    }
  }
}

Exercise 3 solution

public class Ch4Ex3 {
  public static void main(String[] args) {
    
    char letterGrade = 'A';
    int qp;
    
    /* Original code
    switch (letterGrade) 
    { 
     case 'a': case 'A': 
      qp = 4; break; 
     case 'b': case 'B': 
      qp = 3; break; 
     case 'c': case 'C': 
      qp = 2; break; 
     case 'd': case 'D': 
      qp = 1; break; 
     default: 
      qp = 0; break; 
    }
    */
    
    if ( letterGrade == 'A' || letterGrade == 'a' )
      qp = 4;
    else if ( letterGrade == 'B' || letterGrade =='b' )
      qp = 3;
    else if ( letterGrade == 'C' || letterGrade =='c' )
      qp = 2;
    else if ( letterGrade == 'D' || letterGrade == 'd' )
      qp = 1;
    else
      qp = 0;
  }
}

Exercise 4 solution

import java.util.Scanner;

public class Ch4Ex4 {
  
  static Scanner kb = new Scanner(System.in);
  
  public static void main(String[] args) {
    
    String s1, s2;
    
    System.out.print("Enter a string: ");
    s1 = kb.nextLine();
    System.out.print("Enter another string: ");
    s2 = kb.nextLine();
    
    System.out.println("The strings are: \n" + s1 + "\n" + s2 + "\n");
    
    if (s1.compareTo(s2) > 0)
      System.out.println("\"" + s1 + "\" is the greater string.");
    else
      System.out.println("\"" + s2 + "\" is the greater string.");
  }
}

Exercise 5 solution

import java.util.Scanner;

public class Ch4Ex5 {
  
  static Scanner kb = new Scanner(System.in);
  
  public static void main(String[] args) {
    
    String s1, s2;
    
    System.out.print("Enter a string: ");
    s1 = kb.nextLine();
    System.out.print("Enter another string: ");
    s2 = kb.nextLine();
    
    System.out.println("The strings are: \n" + s1 + "\n" + s2 + "\n");
    
    System.out.println("\"" + (s1.compareTo(s2) > 0 ? s1 : s2) + "\" is the greater string.");
    
  }
}

Chapter 5

Exercise 1 solution

import java.util.Scanner;
 
public class Ch5Ex1 {
   
  static Scanner kb = new Scanner(System.in);
 
  public static void main(String[] args) {
     
    int sum = 0;
    int x=0, value;
    double avg;
 
    System.out.print("Enter value #" + (x+1) + " (CTRL-D to end): ");
    while ( kb.hasNext() )
    {
      value = kb.nextInt();
      sum = sum + value;
      x++; 
      System.out.print("Enter value #" + (x+1) + " (CTRL-D to end): ");
    }
 
    // avoid divide by zero.
    if ( x > 0 ) {
      avg = sum / (double)x;
      System.out.println("The sum is " + sum + ".");
      System.out.println("The average is " + avg + ".");
    }
  }
}

Exercise 2 solution

import java.util.Scanner;

public class Ch5Ex2 {
  
  static Scanner kb = new Scanner(System.in);
  
  public static void main(String[] args) {
    char grade;
    int x, qp, qpTotal=0;
    double gpa;
    
    System.out.println("Enter 4 grades and receive the GPA.");
    System.out.println("Each course is considered 4 credits.\n");
    
    for ( x = 1; x < 5; x++ ) {
      System.out.print("Enter grade #" + x + ": ");
      grade = kb.next().charAt(0);
      
      switch (grade) 
      { 
       case 'a': case 'A': 
        qp = 4; break; 
       case 'b': case 'B': 
        qp = 3; break; 
       case 'c': case 'C': 
        qp = 2; break; 
       case 'd': case 'D': 
        qp = 1; break; 
       default: 
        qp = 0; break; 
      }
      
      qpTotal = qpTotal + qp * 4;
    }
    
    gpa = qpTotal / 16.0;
    
    System.out.printf("The GPA is %.2f%n", gpa);
  }
}

Exercise 3 solution

import java.util.Scanner;

public class Ch5Ex3 {
  
  static Scanner kb = new Scanner(System.in);
  
  public static void main(String[] args) {
    char grade;
    int x, qp, qpTotal=0, credits, creditTotal=0;
    double gpa;
    
    System.out.println("Enter 4 grades and the credits for each course");
    System.out.println("You will then receive the GPA.\n");
    
    for ( x = 1; x < 5; x++ ) {
      System.out.print("Enter grade #" + x + ": ");
      grade = kb.next().charAt(0);
      System.out.print("Enter credits for grade #" + x + ": ");
      credits = kb.nextInt();
      
      switch (grade) 
      { 
       case 'a': case 'A': 
        qp = 4; break; 
       case 'b': case 'B': 
        qp = 3; break; 
       case 'c': case 'C': 
        qp = 2; break; 
       case 'd': case 'D': 
        qp = 1; break; 
       default: 
        qp = 0; break; 
      }
      
      creditTotal = creditTotal + credits;
      qpTotal = qpTotal + qp * credits;
    }
    
    gpa = qpTotal / (double)creditTotal;
    
    System.out.printf("The GPA is %.2f%n", gpa);
  }
}

Exercise 4 solution

import java.util.Scanner;
 
public class Ch5Ex4 {
   
  static Scanner kb = new Scanner(System.in);
 
  public static void main(String[] args) {
    
    String line;
    int x, count;
 
    System.out.print("Enter a string (CTRL-D to end): ");
    while ( kb.hasNext() )
    {
      line = kb.nextLine();
      
      count = 0;
      for ( x = 0; x < line.length(); x++ ) {
        char ch = line.charAt(x);
        if ( Character.isLetter(ch) )
          count++;
      }
      System.out.println("There are " + count + " letters.");
      
      count = 0;
      for ( x = 0; x < line.length(); x++ ) {
        char ch = line.charAt(x);
        if ( Character.isWhitespace(ch) )
          count++;
      }
      System.out.println("There are " + count + " whitespace.\n");
      
      System.out.print("Enter a string (CTRL-D to end): ");
    }
  }
}

Chapter 6

Exercise 1 - 3 solutions

public class Ch6Ex1_3 {
  
  /* This piece of code defines and tests the methods from the first
     three exercises of Charpter 6.
  */
  
  // Exercise 1
  public static int sum (int a, int b) {
    return a + b;
  }
  
  // Exercise 2
  public static String concat (String a, String b) {
    return a + b;
  }
  
  // Exercise 3
  public static short sum (short a, short b) {
    /* although the parameters are shorts, the return
       is still treated as an int.
    */
    return (short)(a + b);
  }
  
  public static long sum (long a, long b) {
    return a + b;
  }
  
  public static void main(String[] args) {
    String st1="ABDC", st2="1234";
    int i1=10, i2=15;
    short s1=20, s2=30;
    long l1=50, l2=60;
    
    System.out.println("sum using ints = " + sum(i1, i2));
    System.out.println("concat of two strings = " + concat(st1, st2));
    System.out.println("sum using shorts = " + sum(s1, s2));
    System.out.println("sum using longs = " + sum(l1, l2));
  }
}

Exercise 4 - 5 solutions

public class Ch6Ex4_5 {
  
  // Exercise 4
  public static int indexOf(String s, char c) {
    int x, l;
    
    l = s.length();
    for ( x = 0; x < l; x++)
      if (s.charAt(x) == c)
        return x;
        
    return -1;
  }
  
  // Exercise 5
  public static int rindexOf(String s, char c) {
    int x, l;
    
    l = s.length();
    for ( x = l-1; x >= 0; x--)
      if (s.charAt(x) == c)
        return x;
        
    return -1;
  }
  
  public static void main(String[] args) {
    String t = "The quick brown fox jumps over the lazy dog.";
    
    System.out.println("First forward occurrence of 'o' in t is " + indexOf(t, 'o'));
    System.out.println("First forward occurrence of '?' in t is " + indexOf(t, '?'));
    System.out.println("First reverse occurrence of 'o' in t is " + rindexOf(t, 'o'));
    System.out.println("First reverse occurrence of '?' in t is " + rindexOf(t, '?'));
  }
}

Exercise 6 solution

public class Ch6Ex6 {
  
  /* This solution shows a great opportunity
     for the ternary operator ?:. The if/else
     version is commented out.
  */
  public static String replace(String s, char o, char n) {
    String r = "";
    
    int x, l = s.length();
    for ( x = 0; x < l; x++ ) {
      char c = s.charAt(x);
      /*
      if ( c == o )
        r = r + n;
      else
        r = r + c;
      */
      r += ( c == o ) ? n : c;
    }
    return r;
  }
  
  public static void main(String[] args) {
    
    System.out.println(replace("Mississippi", 's', 'z'));
  }
}

Exercise 7 solution

public class Ch6Ex7 {
  
  /*
    Base conversions are actually quite easy once you devise
    multiplying before you add. The other part is that we are 
    converting from String to int.
    For a char, if it is in the proper range, we can subtract
    '0' from it. So '9' - '0' = 9, '0' - '0' = 0, etc.
  */
  
  public static int parseInt(String s) {
    int x, l = s.length(), sum = 0;
    
    for ( x = 0; x < l; x++) {
      char c = s.charAt(x);
      if ( c >= '0' && c <= '9' )
        sum = sum * 10 + c - '0';
      else
        // Exceptions are discussed in Chapter 12.
        throw new NumberFormatException("Illegal digit '" + c + "'.");
    }
    
    return sum;
  }
  
  public static int parseInt(String s, int r) {
    int x, l = s.length(), sum = 0, d;
    // We can handle up to base 36. Position is digit value.
    String digits = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    
    // Upcase the string to make things easier.
    s = s.toUpperCase();
    for ( x = 0; x < l; x++) {
      char c = s.charAt(x);
      // Get digit value from string or -1 and check range.
      d = digits.indexOf(c);
      if ( d >= 0 && d < r )
        sum = sum * r + d;
      else
        // Exceptions are discussed in Chapter 12.
        throw new NumberFormatException("Illegal digit '" + c + "'.");
    }

    return sum;
  }
  
  public static void main(String[] args) {
    
    System.out.println("parseInt(\"4096\") = " + parseInt("4096"));
    //System.out.println("parseInt(\"409A\") = " + parseInt("409A"));
    System.out.println("parseInt(\"1101001\", 2) = " + parseInt("1101001", 2));
    //System.out.println("parseInt(\"1101002\", 2) = " + parseInt("1101002", 2));
    System.out.println("parseInt(\"177\", 8) = " + parseInt("177", 8));
    //System.out.println("parseInt(\"178\", 8) = " + parseInt("178", 8));
    System.out.println("parseInt(\"4096\", 10) = " + parseInt("4096", 10));
    //System.out.println("parseInt(\"409A\", 10) = " + parseInt("409A", 10));
    System.out.println("parseInt(\"FaCe\", 16) = " + parseInt("FaCe", 16));
    System.out.println("parseInt(\"FaC;\", 16) = " + parseInt("FaC;", 16));

  }
}

Chapter 7a

Chapter 7b

Chapter 8

Chapter 9

Exercise 1 solution

public class Ch9Ex1 {
  public static void main(String[] args) {
    
    int ia[] = new int[25];
    
    // populate with random numbers.
    for (int x = 0; x < ia.length; x++) {
      ia[x] = (int)(Math.random() * 100);
    }
    
    // print 5x5 grid
    for (int x = 0; x< ia.length; x++) {
      System.out.printf("%4d", ia[x]);
      if ( (x+1) % 5 == 0)
        System.out.println();
    }
  }
}

Chapter 9s

Exercise 2 solution

import java.util.Arrays;
import java.util.Vector;

public class Ch9sEx2 {
    
  public static void main(String[] args) {
    
    int median, x, a[] = {4,5,7,8,4,3,2,8,7,4,5,7,8,9,0,1,2,6,7,8,4};
    int cur, ccount, mcount = 0;
    Vector mode = new Vector();
    
    Arrays.sort(a);
    System.out.println(Arrays.toString(a));
    int l = a.length;
    
    // NOTE: This code does NOT handle bi-modal or multi-modal data!
    
    cur = a[0];
    ccount = 1;
    
    for ( x = 0; x < l; x++ ) {
      System.out.println(cur + " " + a[x]);
      if ( cur == a[x] ) {
        ccount++;
      } else {
        System.out.println(cur + " appeared " + ccount + " times.");

        // set the new mode?
        if ( ccount == mcount)
          mode.add(cur);
        if ( ccount > mcount ) {
          //mode = new Vector();
          mode.removeAllElements();
          mode.add(cur);
          mcount = ccount;
        }
        // Always!
        ccount = 1;
        cur = a[x];
      }
    }
      
    System.out.println("The mode is " + mode);

  }
}

Exercise 2 solution

public class Ch9Ex2 {
  
  public static void dumpArray (int[] array) {
    
    int x, l = array.length;
    
    System.out.print("[ ");
    for ( x = 0 ; x < l - 1 ; x++ )
      System.out.print(array[x] + ", ");
      
    System.out.println(array[l-1] + " ]");

  }
  
  public static void main(String[] args) {
    
    int ia1[] = { 10, 20, 30, 40, 50, 60, 70, 80, 90};
    int ia2[] = { 10, 20, 30, 40, 50, 60, 70, 80, 0};

    System.out.println("Removing 40...");
    dumpArray(ia1);
    // remove 40 from ia1.
    for ( int x = 8; x > 3; x--)
      ia1[x-1] = ia1[x];
    dumpArray(ia1);

    System.out.println("\nInserting 99 at first position...");
    dumpArray(ia2);
    // insert at first position.
    for ( int x = 0; x < 8; x++)
      ia2[x+1] = ia2[x];
    ia2[0] = 99;
    dumpArray(ia2);

  }
}

Exercise 3 solution

public class Ch9Ex3 {
  
  public static class ManagedArray {
    
    private int[] ARRAY;
    private int INUSE;
    
    public ManagedArray(int size) {
      INUSE = 0;
      ARRAY = new int[size];
    }
    
    public int size() {
      return ARRAY.length;
    }
    
    // add a value at the end;
    public int add(int val) {
      if ( INUSE >= ARRAY.length )
        return -1;
        
      ARRAY[INUSE] = val;
      INUSE++;
      return INUSE;
    }
    
    // get a value at a apecific index.
    public int get(int pos) {
      /* if pos is out of bounds or there are no 
        * items in the ARRAY, it is an error.
        */
      if ( pos > INUSE || pos < 0 || INUSE == 0 )
        return -1;

      return ARRAY[pos];
    }
    
    // Dump the array. Make it pretty.
    public void dumpArray () {
      
      int x, l = ARRAY.length;
      
      System.out.print("[ ");
      for ( x = 0 ; x < l - 1 ; x++ )
        System.out.print(ARRAY[x] + ", ");
        
      System.out.println(ARRAY[l-1] + " ]");

    }
    
    // Delete the number at pos.
    public int delete(int pos) {
      
      /*
      
      Length is 9, in use is 9. If we call delete
      with pos 2, we loop from 2 to 7. This is due to 
      running off the end with x+1.
      
        0    1    2    3    4    5    6    7    8
        --------------------------------------------
       | 11 | 34 | 56 | -3 | 25 | 78 | 98 | 36 | 10 |
        --------------------------------------------
                    x   x+1                  x   x+1
                   pos
                     BEGIN                    END
                    
                    
      Array after move. In use is now 8.
      
        0    1    2    3    4    5    6    7    8
        --------------------------------------------
       | 11 | 34 | -3 | 25 | 78 | 98 | 36 | 10 | 10 |
        --------------------------------------------

      */
      
      int x;
      
      /* if pos is out of bounds or there are no 
        * items in the ARRAY, it is an error.
        */
      if ( pos > INUSE || pos < 0 || INUSE == 0 )
        return -1;
      
      // Note: if pos == INUSE, no move happens.
      // Also, if pos == 0 and INUSE == 1, 
      // no move happens.  
      for ( x = pos; x < INUSE - 1; x++)
        ARRAY[x] = ARRAY[x+1];
        
      INUSE--;
      return INUSE;
    }
    
    // Insert val at pos.
    public int insert(int pos, int val) {
      
      /*
      
      Length is 9, in use is 8. If we call insert
      with pos 3 and val 99, we loop from 7 to 3.
      This is due to running off the end with x+1.
      
        0    1    2    3    4    5    6    7    8
        --------------------------------------------
       | 11 | 34 | -3 | 25 | 78 | 98 | 36 | 10 | 0  |
        --------------------------------------------
                         x   x+1             x   x+1
                        pos
                          END                BEGIN

      Array after move with INUSE at 9.
                    
        0    1    2    3    4    5    6    7    8
        --------------------------------------------
      | 11 | 34 | -3 | 99 | 25 | 78 | 98 | 36 | 10 |
        --------------------------------------------

      */

      int x;
      
      /* if the array is exhausted, cannot extend here.
        * You can add to one past INUSE, but not past the end 
        * of the array.
        * If pos is out of bounds, it is an error.
        */
      if ( INUSE == ARRAY.length || pos > INUSE + 1
              || pos > ARRAY.length || pos < 0 )
        return -1;
      
      // Note: 
      for ( x = INUSE - 1; x >= pos; x--)
        ARRAY[x+1] = ARRAY[x];
        
      ARRAY[pos] = val;
      INUSE++;
      return INUSE;
    }
  }
    
  public static void main(String[] args) {
  
    int x;
    
    ManagedArray ia = new ManagedArray(10);
    
    // Populate array with 10 random numbers
    for ( x = 0; x < ia.size(); x++ )
      ia.add((int)(Math.random() * 100 + 1));
    
    System.out.println("Original array.");
    ia.dumpArray();
    System.out.println("Value at index 3 is " + ia.get(3));
    System.out.println("\nDeleting at index 3.");
    ia.delete(3);
    ia.dumpArray();
    System.out.println("\nInserting a zero at index 5.");
    ia.insert(5, 0);
    ia.dumpArray();
  }
  
}

Chapter 10

Chapter 11

Chapter 12

Chapter 13

Chapter 14

Chapter 15a

Chapter 15b

Chapter 16

Chapter 17

Chapter 18