Java Programming: Program Design Including Data Structures. Chapter Objectives

Size: px

Start display at page:

Download "Java Programming: Program Design Including Data Structures. Chapter Objectives"

Benedict Turner
5 years ago
Views:

1 Chapter 9: Arrays Java Programming: Program Design Including Data Structures 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 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 2 1

2 Array A structured data type with a fixed number of components A 0 Data 1 Data Data Every component is of the same type Components are accessed using their relative positions in the array A[1] Length: 5 First index: 0 Last index: 4 3 One-Dimensional Arrays Syntax to instantiate an array: datatype[ ] arrayname; arrayname = new datatype[intexp] datatype[ ] arrayname = new datatype[intexp] datatype[ ] arrayname1, arrayname2; Example int[] A; A = new int[5]; int[] B = new int[5]; int[] C = {11, 22, 33, 44, 55; int[] E, F; 4 2

3 One-Dimensional Arrays Syntax to access an array component: arrayname[indexexp] intexp = number of components in array >= 0 0 <= indexexp <= intexp Example A[0] = 100; A[4] = 500; A[2] = A[4] A[0] + 1; A[5] = error (index out of bound) 5 Array num int[] num = new int[5]; 6 3

4 Array list 7 Default Values All entries of an array are first initialized to the proper data type default value. Example int[] A = new A[3]; Currently the array is A[0] = 0 A[1] = 0 A[2] = 0 Type int double boolean String Default Value false (empty) 8 4

5 Using Arrays int[] A; A = new int[5]; //all entries are set to zero int[] E, F; A[0] = 100; A[4] = 500; for (int i=0; i<a.length; i++) { System.out.println(i + " " + A[i]); E = A; //E same as A Specifying Array Size During Program Execution int arraysize; System.out.print("Enter the size of the array: "); arraysize = console.nextint(); int[] list = new int[arraysize];

6 Array Initialization During Declaration double[] sales = {12.25, 32.50, 16.90, 23, 45.68; The values, called initial values, are placed between braces and separated by commas sales[0]= 12.25, sales[1]= 32.50, etc. Array size is determined by the number of initial values within the braces If an array is declared and initialized simultaneously, do not use the operator new to instantiate the array object 11 Arrays and the Instance Variable length A public instance variable length is associated with each array that has been instantiated length contains the size of the array length can be directly accessed in a program using the array name and the dot operator Valid indices of an array (say A) are: 0 A.length - 1 Example: Here list.length is 6 int[] list = {10, 20, 30, 40, 50, 60; List[0] List[5] 12 6

7 Arrays and the Instance Variable length Create the array mylist of 10 components and initialize each component to 0 int[] mylist = new int[10]; The value of mylist.length is Arrays and the Instance Variable length (continued) These statements store 5, 10, 15, and 20, respectively, in the first four components of mylist mylist[0] = 5; mylist[1] = 10; mylist[2] = 15; mylist[3] = 20; Can store the number of filled elements, in the array in a variable, say noofelement 14 7

8 Processing One-Dimensional Arrays Loops used to step through elements in array and perform operations int[] list = new int[100]; int i; for (i = 0; i < list.length; i++) //process list[i], the (i + 1)th //element of list for (i = 0; i < list.length; i++) list[i] = console.nextint(); for (i = 0; i < list.length; i++) System.out.print(list[i] + " "); 15 Arrays Some operations on arrays: Initialize Input data Output stored data Find largest/smallest/sum/average of elements double[] sales = new double[10]; int index; double largestsale, sum, average; 16 8

9 Code to Initialize Array to Specific Value (10.00) for (index = 0; index < sales.length; index++) sales[index] = 10.00; 17 Code to Read Data into Array for (index = 0; index < sales.length; index++) sales[index] = console.nextdouble(); 18 9

10 Code to Print Array for (index = 0; index < sales.length; index++) System.out.print(sales[index] + " "); 19 Code to Find Sum and Average of Array sum = 0; for (index = 0; index < sales.length; index++) sum = sum + sales[index]; if (sales.length!= 0) average = sum / sales.length; else average = 0.0; 20 10

11 Determining Largest Element in Array maxindex = 0; for (index = 1; index < sales.length; index++) if (sales[maxindex] < sales[index]) maxindex = index; largestsale = sales[maxindex]; 21 Determining Largest Element in Array (continued) 22 11

12 Array Index Out of Bounds An array is in bounds if: 0 <= index <= arraysize 1 If index < 0 or index > arraysize: ArrayIndexOutOfBoundsException exception is thrown Base address: location of the first array component 23 Declaring Arrays as Formal Parameters to Methods General syntax to declare an array as a formal parameter: datatype[] arrayname //receiving the call from the caller public static void mymethod1 (int[] lista, double[] listb, int num) { //...do something here //making the call to a method int[] intlist = new int[10]; double[] doublemylist = new double[15]; int number; mymethod1 (intlist, doublemylist, number); 24 12

13 Declaring Arrays as Formal Parameters to Methods Example: Method is called with an array parameter //receiving the call from the caller public static void mymethod1 (int[] lista, double[] listb, int num) { //...do something here... //making the call to a method int[] intlist = {10, 20, 30, 40; Int[] mymethod1 (intlist, doublemylist, number); 25 Declaring Arrays as Formal Parameters to Methods Example: Method is called using an array parameter... int[] intlist = {10, 20, 30, 40; int listsize = intlist.length; mymethod1 (intlist, listsize); for (int i=0; i<listsize; i++) { System.out.println(i + " " + intlist[i]); private static void mymethod1(int[] A, int n) { for (int i=0; i<n; i++) { A[i] += 1; System.out.println(i + " " + A[i]);

14 The Assignment Operators and Arrays 27 The Assignment Operators and Arrays (continued) 28 14

The Assignment Operators and Arrays (continued) for (int index = 0; index < lista.length; index++) listb[index] = lista[index]; 29 Relational Operators Arrays if (lista == listb).

15 The Assignment Operators and Arrays (continued) for (int index = 0; index < lista.length; index++) listb[index] = lista[index]; 29 Relational Operators Arrays if (lista == listb)... The expression lista == listb determines if the values of lista and listb are the same (refer to the same array) To determine whether lista and listb contain the same elements, compare them component by component You can write a method that returns true if two int arrays contain the same elements 30 15

16 Relational Operators and Arrays (continued) boolean isequalarrays(int[] firstarray, int[] secondarray) { if (firstarray.length!= secondarray.length) return false; for (int index = 0; index < firstarray.length; index++) if (firstarray[index]!= secondarray[index]) return false; return true; if (isequalarrays(lista, listb)) Methods for Array Processing //capture data from the keyboard public static void fillarray(int[] list, int noofelements) { int index; for (index = 0; index < noofelements; index++) list[index] = console.nextint(); 32 16

17 Methods for Array Processing (continued) public static void printarray(int[] list, int noofelements) { int index; for (index = 0; index < noofelements; index++) System.out.print(list[index] + " "); public static int sumarray(int[] list, int noofelements) { int index; int sum = 0; for (index = 0; index < noofelements; index++) sum = sum + list[index]; return sum; 33 Methods for Array Processing (continued) public static int indexlargestelement(int[] list, int noofelements) { int index; int maxindex = 0; for (index = 1; index < noofelements; index++) if (list[maxindex] < list[index]) maxindex = index; return maxindex; public static void copyarray(int[] list1, int[] list2, int noofelements) { int index; for (index = 0; index < noofelements; index++) list2[index] = list1[index]; 34 17

18 Parallel Arrays firstname lastname Arrays are parallel if the corresponding components hold related information Maria Macarena 3 Juan 3 Valdez 35 Arrays of Objects Can use arrays to manipulate objects Example: Create an array named array1 with N objects of type T: T[] array1 = new T[N] Can instantiate array1 as follows: for(int j=0; j <array1.length; j++) array1[j] = new T(); 36 18

19 Array of String Objects String[] namelist = new String[5]; namelist[0] = "Amanda Green"; namelist[1] = "Vijay Arora"; namelist[2] = "Sheila Mann"; namelist[3] = "Rohit Sharma"; namelist[4] = "Mandy Johnson"; 37 Array of String Objects (continued) 38 19

20 Arrays of Objects Clock[] arrivaltimeemp = new Clock[100]; 39 Instantiating Array Objects for (int j = 0; j < arrivaltimeemp.length; j++) arrivaltimeemp[j] = new Clock(); 40 20

21 Instantiating Array Objects arrivaltimeemp[49].settime(8, 5, 10); 41 Arrays and Variable Length Parameter List The syntax to declare a variable length formal parameter (list) is: datatype... identifier three dots It could be called using actual parameters such as mymethod (2, 4, 6, 1, 100, 3); mymethod (myarray); 42 21

22 Arrays and Variable Length Parameter List (continued) public static double largest(int... mylist) { double max; int index; if (mylist.length!= 0) { max = list[0]; for (index = 1; index < mylist.length; index++) { if (max < mylist [index]) max = mylist [index]; return max; return 0.0; Instead of: int[] mylist 43 Arrays and Variable Length Parameter List (continued) double num1 = largest(34, 56); double num2 = largest(12.56, 84, 92); double num3 = largest(98.32, 77, 64.67, 56); System.out.println(largest(22.50, 67.78, 92.58, 45, 34, 56)); double[] numberlist = {18. 50, 44, 56.23, , 112.0, 77, 11, 22, 86.62); System.out.println(largest(numberList)); 44 22

23 foreach loop The syntax to use 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 45 foreach loop sum = 0; for (double num : mydoublelist) sum = sum + num; The for statement is read for each num in list The identifier num is initialized to list[0] In the next iteration, the value of num is list[1], and so on 46 23

24 Two-Dimensional Arrays Data is sometimes in table form (difficult to represent using a one-dimensional array) To declare/instantiate a two-dimensional array: datatype[ ][ ] arrayname = new datatype[intexp1][intexp2]; int [][] dayhourtemperature = new int[31][25]; int [][] genderemployeedept = double int [2][10]; 47 Two-Dimensional Arrays To access a component of a two-dimensional array: arrayname[indexexp1][indexexp2]; intexp1, intexp2 >= 0 indexexp1 = row position indexexp2 = column position dayhourtemperature[01][01] = 41; dayhourtemperature[01][24] = 40; dayhourtemperature[30][24] = 38; 48 24

Two-Dimensional Arrays (continued) Can specify different number of columns for each row (ragged arrays) Three ways to process two-dimensional arrays: Entire array Particular row of array (row

25 Two-Dimensional Arrays (continued) Can specify different number of columns for each row (ragged arrays) Three ways to process two-dimensional arrays: Entire array Particular row of array (row processing) Particular column of array (column processing) Processing algorithms is similar to processing algorithms of one-dimensional arrays 49 Two-Dimensional Arrays (continued) double[][]sales = new double[10][5]; 50 25

26 Accessing Two-Dimensional Array Components 51 Two-Dimensional Arrays: Special Cases 52 26

27 Two-Dimensional Arrays: Processing Initialization for (row = 0; row < matrix.length; row++) for (col = 0; col < matrix[row].length; col++) matrix[row][col] = 10; Print for (row = 0; row < matrix.length; row++) { for (col = 0; col < matrix[row].length; col++) System.out.printf("%7d", matrix[row][col]); System.out.println(); 53 Input Two-Dimensional Arrays: Processing (continued) for (row = 0; row < matrix.length; row++) for (col = 0; col < matrix[row].length; col++) matrix[row][col] = console.nextint(); Sum by Row for (row = 0; row < matrix.length; row++) { sum = 0; for (col = 0; col < matrix[row].length; col++) sum = sum + matrix[row][col]; System.out.println("Sum of row " + (row + 1) + " = "+ sum); 54 27

28 Sum by Column Two-Dimensional Arrays: Processing (continued) for (col = 0; col < matrix[0].length; col++) { sum = 0; for (row = 0; row < matrix.length; row++) sum = sum + matrix[row][col]; System.out.println("Sum of column " + (col + 1) + " = " + sum); 55 Two-Dimensional Arrays: Processing (continued) Largest Element in Each Row for (row = 0; row < matrix.length; row++) { largest = matrix[row][0]; for (col = 1; col < matrix[row].length; col++) if (largest < matrix[row][col]) largest = matrix[row][col]; System.out.println("The largest element of row " + (row + 1) + " = " + largest); 56 28

29 Two-Dimensional Arrays: Processing (continued) Largest Element in Each Column for (col = 0; col < matrix[0].length; col++) { largest = matrix[0][col]; for (row = 1; row < matrix.length; row++) if (largest < matrix[row][col]) largest = matrix[row][col]; System.out.println("The largest element of col " + (col + 1) + " = " + largest); 57 Multidimensional Arrays Can define three-dimensional arrays or n-dimensional arrays (n can be any number) Syntax to declare and instantiate array: datatype[][] [] arrayname = new datatype[intexp1][intexp2] [intexpn]; Syntax to access component: arrayname[indexexp1][indexexp2] [indexexpn] intexp1, intexp2,..., intexpn = positive integers indexexp1,indexexp2,..., indexexpn = non-negative integers 58 29

30 Loops to Process Multidimensional Arrays double[][][] cardealers = new double[10][5][7]; For (i = 0; i < 10; i++) for (j = 0; j < 5; j++) for (k = 0; k < 7; k++) cardealers[i][j][k] = 10.00; 59 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 each letter appears in text 60 30

31 Programming Example Solution: Text Processing An array of 26 representing the letters in the alphabet Three methods: copytext charactercount writetotal Value in appropriate index is incremented using methods and depends on character read from text 61 Chapter Summary Arrays Definition Uses Different arrays One-dimensional Two-dimensional Multidimensional (n-dimensional) Arrays of objects Parallel arrays 62 31

32 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 63 32

Spring 2010 Java Programming

Spring 2010 Java Programming Java Programming: Guided Learning with Early Objects Chapter 7 - Objectives Learn about arrays Explore how to declare and manipulate data in arrays Learn about the instance variable length Understand the