Java Programming: From Problem Analysis to Program Design, 3e Chapter 9

1
Java Programming From Problem Analysis to
Program Design, 3eChapter 9

• Arrays

2
Chapter Objectives

• Learn about arrays
• Explore how to declare and manipulate data into
  arrays
• Understand the meaning of array index out of
  bounds
• Become familiar with the restrictions on array
  processing

3
Chapter Objectives (continued)

• Discover how to pass an array as a parameter to a
  method
• Discover how to manipulate data in a
  two-dimensional array
• Learn about multidimensional arrays

4
Array

• Definition structured data type with a fixed
  number of elements
• Elements of an array are also called components
  of the array
• Every element is of the same type
• Elements are accessed using their relative
  positions in the array

5
One-Dimensional Arrays
6
One-Dimensional Arrays (continued)
7
One-Dimensional Arrays (continued)

• intExp number of components in array gt 0
• 0 lt indexExp lt intExp

8
Array numint num new int5
Arrays
9
Array List
10
Array List (continued)
11
Array List (continued)
12
Array List (continued)
13

• Specifying Array Size During Program Execution

14
Array Initialization During Declaration

• The initializer list contains values, called
  initial values, that are placed between braces
  and separated by commas
• Here, sales0 12.25, sales1 32.50, sales2
  16.90, sales3 23.00, and sales4 45.68

15
Array Initialization During Declaration
(continued)

• When declaring and initializing arrays, the size
  of the array is determined by the number of
  initial values within the braces
• If an array is declared and initialized
  simultaneously, we do not use the operator new to
  instantiate the array object

16
Arrays and the Instance Variable length

• Associated with each array that has been
  instantiated, there is a public (final) instance
  variable length
• The variable length contains the size of the
  array
• The variable length can be directly accessed in a
  program using the array name and the dot operator
• int list 10, 20, 30, 40, 50, 60

17
Arrays and the Instance Variable length
(continued)

• This statement creates the array list of six
  components and initializes the components using
  the values given
• Here list.length is 6
• int numList new int10
• This statement creates the array numList of 10
  components and initializes each component to 0

18
Arrays and the Instance Variable length
(continued)

• The value of numList.length is 10
• numList0 5
• numList1 10
• numList2 15
• numList3 20
• These statements store 5, 10, 15, and 20,
  respectively, in the first four components of
  numList
• You can store the number of filled elements, that
  is, the actual number of elements, in the array
  in a variable, say numOfElement
• It is a common practice for a program to keep
  track of the number of filled elements in an array

19
Processing One-Dimensional Arrays

• Loops used to step through elements in array and
  perform operations
• int list new int100
• int i
• for (i 0 i lt list.length i)
• //process listi, the (i 1)th
• //element of list
• for (i 0 i lt list.length i)
• listi console.nextInt()
• for (i 0 i lt list.length i)
• System.out.print(listi " ")

20
Arrays (continued)

• Some operations on arrays
• Initialize
• Input data
• Output stored data
• Find largest/smallest/sum/average of elements

double sales new double10 int
index double largestSale, sum, average
21
Code to Initialize Array to Specific Value (10.00)
for (index 0 index lt sales.length
index) salesindex 10.00
22
Code to Read Data into Array
for (index 0 index lt sales.length
index) salesindex
console.nextDouble()
23
Code to Print Array
for (index 0 index lt sales.length
index) System.out.print(salesindex
" ")
24
Code to Find Sum and Average of Array
sum 0 for (index 0 index lt sales.length
index) sum sum
salesindex if (sales.length ! 0) average
sum / sales.length else average 0.0
25
Determining Largest Element in Array
maxIndex 0 for (index 1 index lt
sales.length index) if
(salesmaxIndex lt salesindex) maxIndex
index largestSale salesmaxIndex
26
Determining Largest Element in Array (continued)
27
Determining Largest Element in Array (continued)
28
Array Index Out of Bounds

• Array in bounds if
• 0 lt index lt arraySize 1
• If index lt 0 or index gt arraySize
• ArrayIndexOutOfBoundsException exception is
  thrown
• Base address memory location of first component
  in array

29
Declaring Arrays as Formal Parameters to Methods

• A general syntax to declare an array as a formal
  parameter
• dataType arrayName
• public static void arraysAsFormalParameter(int
  listA,
• double listB, int num)
• //...
• int intList new int10
• double doubleNumList new double15
• int number
• arraysAsFormalParameter(intList, doubleNumList,
  number)

30
The Assignment Operators and Arrays
31
The Assignment Operators and Arrays (continued)
32
The Assignment Operators and Arrays (continued)
33
Relational Operators Arrays

• if (listA listB)...
• - The expression listA listB determines if the
  values of listA and listB are the same and thus
  determines whether listA and listB refer to the
  same array
• - To determine whether listA and listB contain
  the same elements, you need to compare them
  component by component
• - You can write a method that returns true if two
  int arrays contain the same elements

34
Relational Operators and Arrays (continued)
boolean isEqualArrays(int firstArray,
int secondArray) if
(firstArray.length ! secondArray.length)
return false for (int index 0 index lt
firstArray.length
index) if (firstArrayindex !
secondArrayindex) return false
return true if (isEqualArrays(listA,
listB)) ...
35
Arrays as Parameter Methods
36
Methods for Array Processing
37
Methods for Array Processing (continued)
38
Methods for Array Processing (continued)
39
Methods for Array Processing (continued)
40
Parallel Arrays

• Arrays are parallel if corresponding components
  hold related information

41
Arrays of Objects

• Can use arrays to manipulate objects
• Example create array named array1 with N objects
  of type T
• T array1 new TN
• Can instantiate array1 as follows
• for(int j0 j ltarray1.length j)
• array1j new T()

42
Array of String Objects

• String nameList new String5
• nameList0 "Amanda Green"
• nameList1 "Vijay Arora"
• nameList2 "Sheila Mann"
• nameList3 "Rohit Sharma"
• nameList4 "Mandy Johnson"

43
Array of String Objects (continued)
44
Clock arrivalTimeEmp new Clock100
Arrays of Objects (continued)
45
Instantiating Array Objects
for (int j 0 j lt arrivalTimeEmp.length j)
arrivalTimeEmpj new Clock()
46
Instantiating Array Objects (continued)
arrivalTimeEmp49.setTime(8, 5, 10)
47
Arrays and Variable Length Parameter List

• The syntax to declare a variable length formal
  parameter (list) is
• dataType ... identifier

48
Arrays and Variable Length Parameter List
(continued)
49
Arrays and Variable Length Parameter List
(continued)
50
Arrays and Variable Length Parameter List
(continued)

• A method can have both a variable length formal
  parameter and other formal parameters consider
  the following method heading
• public static void myMethod(String name, double
  num, int ... intList)
• The formal parameter name is of type String, the
  formal parameter num is of type double, and the
  formal parameter intList is of variable length
• The actual parameter corresponding to intList can
  be an int array or any number of int variables
  and/or int values

51
Arrays and Variable Length Parameter List
(continued)

• A method can have at most one variable length
  formal parameter
• If a method has both a variable length formal
  parameter and other types of formal parameters,
  then the variable length formal parameter must be
  the last formal parameter of the formal parameter
  list

52
foreach loop

• The syntax to use this for loop to process the
  elements of an array is
• for (dataType identifier arrayName)
• statements
• identifier is a variable and the data type of
  identifier is the same as the data type of the
  array components

53
foreach loop (continued)

• sum 0
• for (double num list)
• sum sum num
• The for statement in Line 2 is read for each num
  in list
• The identifier num is initialized to list0
• In the next iteration, the value of num is
  list1, and so on
• for (double num numList)
• if (max lt num)
• max num

54
Two-Dimensional Arrays
55
Two-Dimensional Arrays (continued)
56
double sales new double105
Two-Dimensional Arrays (continued)
57
Accessing Array Elements

• intExp1, intExp2 gt 0
• indexExp1 row position
• indexExp2 column position

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Accessing Array Elements (continued)
59
Two-Dimensional Arrays and the Instance Variable
length

• This statement declares and instantiates a
  two-dimensional array matrix of 20 rows and 15
  columns
• The value of the expression
• matrix.length
• is 20, the number of rows

60
Two-Dimensional Arrays and the Instance Variable
length (continued)

• Each row of matrix is a one-dimensional array
  matrix0, in fact, refers to the first row
• The value of the expression
• matrix0.length
• is 15, the number of columns in the first row
• matrix1.length gives the number of columns in
  the second row, which in this case is 15, and so
  on

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Two-Dimensional Arrays Special Cases
62
Two-Dimensional Arrays Special Cases (continued)

• Create columns

63
Two-Dimensional Array Initialization During
Declaration
64
Two-Dimensional Array Initialization During
Declaration (continued)

• To initialize a two-dimensional array when it is
  declared
• - The elements of each row are enclosed within
  braces and separated by commas
• - All rows are enclosed within braces

65
Two-Dimensional Array Initialization During
Declaration (continued)
66
Two-Dimensional Arrays (continued)

• Three ways to process 2-D arrays
• Entire array
• Particular row of array (row processing)
• Particular column of array (column processing)
• Processing algorithms similar to processing
  algorithms of one-dimensional arrays

67
Two-Dimensional Arrays Processing
Initialization for (row 0 row lt
matrix.length row) for (col 0 col lt
matrixrow.length col)
matrixrowcol 10
Print for (row 0 row lt matrix.length
row) for (col 0 col lt
matrixrow.length col)
System.out.printf("7d",
matrixrowcol) System.out.println()
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Two-Dimensional Arrays Processing (continued)
Input for (row 0 row lt matrix.length row)
for (col 0 col lt matrixrow.length
col) matrixrowcol
console.nextInt()
Sum by Rowfor (row 0 row lt matrix.length
row) sum 0 for (col 0 col lt
matrixrow.length col)
sum sum matrixrowcol
System.out.println("Sum of row " (row 1)
" " sum)
69
Two-Dimensional Arrays Processing (continued)
Sum by Column for (col 0 col lt
matrix0.length col) sum 0 for
(row 0 row lt matrix.length row)
sum sum matrixrowcol
System.out.println("Sum of column " (col 1)
" " sum)
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Two-Dimensional Arrays Processing (continued)
Largest Element in Each Row for (row 0 row lt
matrix.length row) largest
matrixrow0 for (col 1 col lt
matrixrow.length col)
if (largest lt matrixrowcol)
largest matrixrowcol
System.out.println("The largest element of row "
(row 1) " "
largest)
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Two-Dimensional Arrays Processing (continued)
Largest Element in Each Column for (col 0 col
lt matrix0.length col) largest
matrix0col for (row 1 row lt
matrix.length row) if (largest lt
matrixrowcol) largest
matrixrowcol System.out.println("The
largest element of col "
(col 1) " " largest)
72
Multidimensional Arrays

• Can define three-dimensional arrays or
  n-dimensional array (n can be any number)
• Syntax to declare and instantiate array
• dataType arrayName new
• dataTypeintExp1intExp2intExpn
• Syntax to access component
• arrayNameindexExp1indexExp2indexExpn
• intExp1, intExp2, ..., intExpn positive
  integers
• indexExp1,indexExp2, ..., indexExpn
  non-negative integers

73
Loops to Process Multidimensional Arrays
double carDealers new double1057
for (i 0 i lt 10 i) for (j 0 j lt 5
j) for (k 0 k lt 7 k)
carDealersijk 10.00
74
Programming Example Text Processing

• Program reads given text outputs the text as
  is prints number of lines and number of times
  each letter appears in text
• Input file containing text to be processed
• Output file containing text, number of lines,
  number of times letter appears in text

75
Programming Example Solution Text Processing

• An array of 26 representing the letters in the
  alphabet
• Three methods
• copyText
• characterCount
• writeTotal
• Value in appropriate index incremented using
  methods and depending on character read from text
  

76
Chapter Summary

• Arrays
• Definition
• Uses
• Different Arrays
• One-dimensional
• Two-dimensional
• Multidimensional (n-dimensional)
• Arrays of objects
• Parallel arrays

77
Chapter Summary (continued)

• Declaring arrays
• Instantiating arrays
• Processing arrays
• Entire array
• Row processing
• Column processing
• Common operations and methods performed on arrays
• Manipulating data in arrays