Chapter 2:  "Objects, Control Structures, Arrays"

Data Structures with Java, Rick Mercer

Answers to Self-Check Questions



2-1 finish the assertions

      BankAccount b1 = new BankAccount("Kim", 0.00);
      BankAccount b2 = new BankAccount("Chris", 500.00);
      assertEquals( "Kim" , b1.getID()); //filled in "Kim"
      assertEquals( "Chris" , b2.getID()); //filled in "Chris
 
      b1.deposit(222.22);
      b1.withdraw(20.00);
      assertEquals( 202.22 , b1.getBalance(), 0.001); //filled in 202.22

      b2.deposit(55.55);
      b2.withdraw(10.00);
      assertEquals( 545.55  , b2.getBalance(), 0.001); //filled in 545.55


2-2 explain error
      -a- missing value as second parameter
      -b- missing " = new BankAccount"
      -c- "Account" should be "BankAccount"
      -d- there are no parameters
      -e- the parameter should be a double
      -f- "Deposit" is not a method (deposit is the method)
      -g- missing object reference
      -h- b4 has not been instantiated
      -i- there is no method called name parameter symbol for the "getBalance()" method
      -j- missing "()" after method call
 
2-3 value of positionOfG = 6
           
2-4 value of 3 = "ef"
           
2-5 value of len = 8
          
2-6 output =   Wheatley, Kay

2-7 int midInt = str.length() / 2;
    String mid = "" + str.charAt(midInt);

2-8 a,b,c, and f have errors. d -> 3   e -> "y S"

2-9 -a- String
    -b- concat
    -c- 1
    -d- String
    -e- none
 
2-10 return values or invalid
  -a- abcxyz
  -b- invalid - no paramter passed
  -c- invalid - parameter is not a String
  -d- invalid - two parameters passed when only one needed
  -e- abcwx yz
  -f- invalid - concat is not a static method
           
2-11 fill in blanks
   String s = "abc";
   assertEquals(  "abc!" , s.concat("!")); //added "abc!"
   assertEquals( "abccba" , s.concat("cba")); //added "abccba"
   assertEquals( "abc123" , s.concat("123")); //added "abc123"
 
2-12 isOdd method

  public boolean isOdd (int num){
     return num % 2 != 0;
	//Java has does not handle negatives correctly with the mod operator.
  }



2-13 averageThree method

    public double averageThree(double one, double two, double three) {
        return (one+two+three)/3.0;
    }


2-14 firstLast  method
 
    public String firstLast(String str){
        String result = "" + str.charAt(0) + str.charAt(str.length()-1);
        return result;
    }

2-15 which assertion would pass?  ==  assertion "a"

2-16 which would pass?  ==  "b" and "c"

2-17 assertions for isLeapYear. Your answer may vary: Check 4 end of century's where 1 is and three are not. Check some that are not end of century that are evenly divisible by 4 with others that are not.

    assertTrue(isLeapYear(1600));
    assertTrue(isLeapYear(2000));
    assertTrue(isLeapYear(2008));
    assertTrue(isLeapYear(2400));
    assertFalse(isLeapYear(2100));
    assertFalse(isLeapYear(2005));
    assertFalse(isLeapYear(2006));
    assertFalse(isLeapYear(2007));


2-18 isLeapYear method.

   public boolean isLeapYear(int year)  {
       if(year % 4 == 0)//general leap year case  {
          if(year % 100 != 0 || year % 400 == 0)/*if the year is not divisible by 100 or is also disvisible by 400*/
              return true;
       }
       return false;//everything else falls through to here
   }
 

2-19 assertions for largest method

   assertEquals(4, largest(1, 2, 4));
   assertEquals(7, largest(7, 6, 5));
   assertEquals(7, largest(5, 7, 5));
   assertEquals(1, largest(-3, -2, 1));
   assertEquals(0, largest(-2, 0, -1));
   assertEquals(5, largest(5, 5, 5));

2-20 largest method

   public int largest(int one, int two, int three) {
       return Math.max(Math.max(one, two), three);
   }

 
2-21 letterGrade method

  public String letterGrade(int grade) {
      if (grade < 0 || grade > 100)
          return "?";
      else if (grade < 60)
          return "F";
      else if (grade < 70)
          return "D";
      else if (grade < 80)
          return "C";
      else if (grade < 90)
          return "B";
      else
          return "A";
  }

 
2-22 write the output
  -a- 1 2 3 4
  -b- 1 2 3 4 5
  -c- -3 -1 1 3
  -d- 5 4 3 2 1
  -e- before  after
  -f- an error (j not instantiated)



2-23 for loop 10 to 1

    for (int i = 10; i >= 1; i--) {
      System.out.print(i + " ");
    }

 

2-24 for loop output
  -a- 2  4  6  8  10
  -b-  compiler error - need "int counter = 10;" if counter is initialized prior, then:
1
2
3
4
5
6
7
8
9
10
 
2-25 number of times "Hello" is printed

  -a- 20 times
  -b- zero
  -c- infinite
  -d- infinite
 
trace through answers

  2-26 == 29 (correct)
  2-27 == 4 (correct)
  2-28 == -999999994 (incorrect)

 
2-29 b-when the input is entered in ascending order
Also, when a valid int excedes the range of -999999999 and 999999999


2-30 how to correct?

Initialize hi and low to the 1st number in the list, and compare all other numbers to both


/////////////////////////////////////////////////////////////////
Arrays

2-31 value == 0

2-32 100 values can be stored

2-33 index 0 accesses the first element

2-34 index 99 accesses the last element


2-35 fill the array

  for(int i = x.length-1; i>=0; i--){
      x[i] = 100-i;
  }


2-36 print array elements on separate lines

  for(int i = 0; i<x.length; i++){
            System.out.println(x[i]);
  }

2-37  throws an ArrayIndexOutOfBoundsException


2-38 output
  0  9
  1  8
  2  7
  3  6
  4  5

 
2-39 assertions

  assertEquals(11, sum(x, 6));
  assertEquals(6, sum(x, 3));
  assertEquals(1, sum(x, 1));


2-40 sum method

  public int sum (int[] nums, int n){
      int result = 0;
      if(n > 0 && n <= nums.length){
         for (int i = 0; i<n; i++){
               result += nums[i];
         }
      }
      return result;
  }

 
2-41 value of [1][2] = 0

2-42 Java throws an ArrayIndexOutOfBoundsException if the indicies do not work with the array

2-43 12 elements stored properly

2-44 row range is from 0 to 2

2-45 column range is from 0 to 3

2-46 initializing an array

  for(int i = 0; i<3; i++){
      for(int j = 0; i<4; i++){
            a[i][j] = 999;
      }
  }


2-47 double [][] sales =  new double [10][12];

2-48 double [][] sales2 = new double [12][10];