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Java, Java, Java: Object-Oriented Problem Solving, 2024E

Ralph Morelli, Ralph Walde, Beryl Hoffman, David G. Cooper

Section 9.13 Chapter Summary

Subsection 9.13.1 Technical Terms

array initializer array length
binary search data structure
element element type
insertion sort multidimensional array
one-dimensional array polymorphic sort method
selection sort sequential search
sorting subscript
two-dimensional array

Subsection 9.13.2 Important Points

  • An array is a named collection of contiguous storage locations, each of which stores a data item of the same data type. Each element of an array is referred to by a subscript —that is, by its position in the array. If the array contains N elements, then its length is N and its indexes are 0, 1, … , N-1.
  • Array elements are referred to using the following subscript notation arrayname[subscript], where arrayname is any valid identifier, and subscript is an integer value in the range 0 to arrayname.length - 1. The array’s length instance variable can be used as a bound for loops that process the array.
  • An array declaration provides the name and type of the array. An array instantiation uses the keyword new and causes the compiler to allocate memory for the array’s elements: 
    int arr[]; // Declare a one-dimensional array variable
arr = new int[15];// Allocate 15 int locations for it
  • Multidimensional arrays have arrays as their components: 
    int twoDarr[][]; // Declare a two-dimensional array variable
twoDarr = new int[10][15]; // Allocate 150 int locations
  • An array’s values must be initialized by assigning values to each array location. An initializer expression may be included as part of the array declaration.
  • Insertion sort and selection sort are examples of array sorting algorithms. Both algorithms require several passes over the array.
  • When an array is passed as a argument to a method, a reference to the array is passed rather than the entire array itself.
  • Swapping two elements of an array, or any two locations in memory, requires the use of a temporary variable.
  • Sequential search and binary search are examples of array searching algorithms. Binary search requires that the array be sorted.
  • For multidimensional arrays, each dimension of the array has its own length variable.
  • Inheritance and polymorphism are useful design features for developing a hierarchy of computer games.

Solutions 9.13.3 Solutions to Self-Study Exercises

9.2 One-Dimensional Arrays
9.2.3 Array Allocation

Self-Study Exercises
9.2.3.1. How many bytes int array?
Solution.
20 bytes
9.2.3.2. How many bytes double array?
Solution.
80 bytes
9.2.3.3. How many bytes char array?
Solution.
60 bytes
9.2.3.4. How many bytes String array?
Solution.
40 bytes
9.2.3.5. How many bytes Student array?
Solution.
20 bytes

9.2.5 Assigning and Using Array Values

Self-Study Exercises
9.2.5.1. What’s the value?
Solution.
farr[1] == 2.2
9.2.5.2. What’s the value?
Solution.
farr[farr.length - 2] == 4.4
9.2.5.3. Access the last element.
Solution.
A, B and D
9.2.5.4. Assign to the first element.
Solution.
D
9.2.5.5.
Solution.
double farr[] = {1.1, 2.2, 3.3, 4.4, 5.5};
for (int k=0; k < farr.length; k++) {
  System.out.print(farr[k] + " ");
}

9.3 Simple Array Examples

Self-Study Exercise
9.3.1. Square Roots.
Solution.

9.4 Example: Counting Letter Frequencies
9.4.2 A Class to Count Letter Frequencies

Self-Study Exercises
9.4.2.1. Letter Frequencies.
Solution.
public static void main(String[] argv) {
  AnalyzeFreq af = new AnalyzeFreq();
  af.countLetters("Now is the time for all good students" +
    " to study computer related topics.");
  af.printArray();
} //main()

9.5 Array Algorithms: Sorting
9.5.1 Insertion Sort

Self Study Exercise
9.5.1.1. Run Insertion Sort.
Solution.
Use Codelens to step through the insertion sort algorithm.
9.5.1.2. Insertion sort trace 1.
Solution.
Answer: 18 24 90 1 0 85 34 18
The first pass would insert 18 before 24:
24 18 90 1  0  85 34 18 // Initial
18 24 90 1  0  85 34 18 // Pass 1
9.5.1.3. Insertion sort trace 2.
Solution.
Answer: 0 1 18 24 90 85 34 18
The entire sort would go like this:
24 18 90 1  0  85 34 18 // Initial
18 24 90 1  0  85 34 18 // Pass 1
18 24 90 1  0  85 34 18 // Pass 2
1  18 24 90 0  85 34 18 // Pass 3
0  1  18 24 90 85 34 18 // Pass 4 
0  1  18 24 85 90 34 18 // Pass 5
0  1  18 24 34 85 90 18 // Pass 6
0  1  18 18 24 34 85 90 // Pass 7

9.5.2 Selection Sort

Self-Study Exercises
9.5.2.1. Selection sort trace 1.
Solution.
Answer: >0 18 90 1 24 85 34 18
The first pass would select the smallest number and place it in the first array location:
24 18 90 1   0   85 34 18 // Initial
0  18 90 1   24  85 34 18 // Pass 1
9.5.2.2. Selection sort trace 2.
Solution.
Answer: 0 1 18 18 24 85 34 90
The four smallest numbers would be sorted at the left of the array.
24 18 90 1   0   85 34 18 // Initial
0  18 90 1   24  85 34 18 // Pass 1
0  1  90 18  24  85 34 18 // Pass 2
0  1  18 90  24  85 34 18 // Pass 3
0  1  18 18  24  85 34 90 // Pass 4
0  1  18 18  24  85 34 90 // Pass 5
0  1  18 18  24  34 85 90 // Pass 6
0  1  18 18  24  34 85 90 // Pass 7

9.5.3 Algorithm: Swapping Memory Elements

Self-Study Exercises
9.5.3.1. Swapping values in variables.
Solution.
double temp = 0;
temp = var1;
var1 = var2;
var2 = temp;

9.5.4 Passing a Value and Passing a Reference

Self-Study Exercise
9.5.4.1. Array Parameter.
Solution.
Answer: 1,2,3,5,5. The change in the myArr[3] will persist after the method finishes.
9.5.4.2. What’s the value?
Solution.
Answer: 3 Even though the parameter m is changed within the method, that change will not affect k, which is a value argument.
9.5.4.3. Selection sort.
Solution.
smallest = k; 
for (int i k+1; i<arr.length; i++) {
   if (arr[i] < arr[smallest])
     smallest = j;
}
swap(arr, k, smallest);

9.6 Array Algorithms: Searching
9.6.2 Binary Search

Self-Study Exercise
9.6.2.1. Binary search.
Solution.
Answer: 6, 10, 8, 9
key  iteration  low   high    mid
21   0          0     13      6
21   1          7     13      10
21   2          7     9       8
21   3          9     9       9
21   4          10    9       failure

9.7 Two-Dimensional Arrays
9.7.1 Example: Rainfall Array

Self-Study Exercises
9.7.1.1. Two-D array.
Solution.

9.7.3 Passing Part of an Array to a Method

Self-Study Exercises
9.7.3.1. Newspaper sales.
Solution.

9.9 OBJECT-ORIENTED DESIGN: Polymorphic Sorting (Optional)
9.9.3 The java.util.Arrays.sort() Method

Self-Study Exercises
9.9.3.1. Polymorphic Sort.
Solution.
  1. A compareTo() for LetterFreq:
    public int compareTo(Object lf) {
    LetterFreq  letFreq = (LetterFreq)lf;
    if (freq < letFreq.getFreq())
        return -1;
    else if (freq > letFreq.getFreq())
        return +1;
    else return 0; //The frequencies must be equal.
} //compareTo()
  2. A sort() for AnalyzeFreq:
    public void sort() {
    java.util.Arrays.sort(freqArr);
} //sort()
  3. A new AnalyzeFreq.main() that uses sort():
    public static void main(String[] argv) {
  AnalyzeFreq af = new AnalyzeFreq();
  af.countLetters("Now is the time for all good students" +
    " to study computer-related topics.");
  af.sort();
  af.printArray();
} //main()
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