1. www.site.uottawa.ca/~elsaddik 1 (c) elsaddik CSI 1102 Introduction to Software Design Prof. Dr.-Ing. Abdulmotaleb El Saddik University of Ottawa (SITE 5-037) (613) 562-5800 x 6277 elsaddik @ site.uottawa.ca abed @ mcrlab.uottawa.ca http://www.site.uottawa.ca/~elsaddik/

2. www.site.uottawa.ca/~elsaddik 2 (c) elsaddik Arrays Arrays are objects that help us organize large amounts of information Chapter 6 focuses on:  array declaration and use  passing arrays and array elements as parameters  arrays of objects  sorting elements in an array  multidimensional arrays  the ArrayList class  polygons and polylines  more button components

3. www.site.uottawa.ca/~elsaddik 3 (c) elsaddik Arrays An array is an ordered list of values 0 1 2 3 4 5 6 7 8 9 79 87 94 82 67 98 87 81 74 91 An array of size N is indexed from zero to N-1 scores The entire array has a single name Each value has a numeric index This array holds 10 values that are indexed from 0 to 9

4. www.site.uottawa.ca/~elsaddik 4 (c) elsaddik Arrays  A particular value in an array is referenced using the array name followed by the index in brackets  For example, the expression scores[2] refers to the value 94 (which is the 3rd value in the array)  That expression represents a place to store a single integer which can be used wherever an integer variable can be used

5. www.site.uottawa.ca/~elsaddik 5 (c) elsaddik Arrays  For example, value in an array can be assigned a value, printed, or used in a calculation  scores[2] = 89;  scores[first] = scores[first] + 2;  mean = (scores[0] + scores[9])/2;  System.out.println (“Top = “ + scores[5]);

6. www.site.uottawa.ca/~elsaddik 6 (c) elsaddik Arrays  An array stores multiple values of the same type  That type can be primitive types or object references  Therefore, we can create an array of integers, or an array of characters, or an array of String objects, etc.  In Java, the array itself is an object  Therefore the name of the array is a object reference variable, and the array itself must be instantiated

7. www.site.uottawa.ca/~elsaddik 7 (c) elsaddik Declaring Arrays  The scores array could be declared as follows: int[] scores = new int[10];  Note that the type of the array does not specify its size, but each object of that type has a specific size  The type of the variable scores is int[] (an array of integers)  It is set to a new array object that can hold 10 integers See BasicArray.java (page xxx) BasicArray.java

8. www.site.uottawa.ca/~elsaddik 8 (c) elsaddik BasicArray.java public class BasicArray { final static int LIMIT = 15; final static int MULTIPLE = 10; //----------------------------------------------------------------- // Creates an array, fills it with various integer values, // modifies one value, then prints them out. //----------------------------------------------------------------- public static void main (String[] args) { int[] list = new int[LIMIT]; // Initialize the array values for (int index = 0; index < LIMIT; index++) list[index] = index * MULTIPLE; list[5] = 999; // change one array value for (int index = 0; index < LIMIT; index++) System.out.print (list[index] + " "); System.out.println (); }

9. www.site.uottawa.ca/~elsaddik 9 (c) elsaddik Declaring Arrays  Some examples of array declarations: float[] prices = new float[500]; boolean[] flags; flags = new boolean[20]; char[] codes = new char[1750];

10. www.site.uottawa.ca/~elsaddik 10 (c) elsaddik Bounds Checking  Once an array is created, it has a fixed size  An index used in an array reference must specify a valid element  That is, the index value must be in bounds (0 to N-1)  The Java interpreter throws an ArrayIndexOutOfBoundsException if an array index is out of bounds  This is called automatic bounds checking

11. www.site.uottawa.ca/~elsaddik 11 (c) elsaddik Bounds Checking  For example, if the array codes can hold 100 values, it can be indexed using only the numbers 0 to 99  If count has the value 100, then the following reference will cause an exception to be thrown: System.out.println (codes[count]);  It’s common to introduce off-by-one errors when using arrays for (int index=0; index <= 100; index++) codes[index] = index*50 + epsilon; problem

12. www.site.uottawa.ca/~elsaddik 12 (c) elsaddik Bounds Checking  Each array object has a public constant called length that stores the size of the array  It is referenced using the array name (just like any other object): scores.length  Note that length holds the number of elements, not the largest index See ReverseOrder.java (page xxx) ReverseOrder.java See LetterCount.java (page xxx) LetterCount.java

13. www.site.uottawa.ca/~elsaddik 13 (c) elsaddik ReverseOrder.java import cs1.Keyboard; public class ReverseOrder { public static void main (String[] args) { double[] numbers = new double[10]; System.out.println ("The size of the array: " + numbers.length); for (int index = 0; index < numbers.length; index++) { System.out.print (“ Enter number " + (index+1) + ": "); numbers[index] = Keyboard.readDouble(); } System.out.println ("The numbers in reverse order:"); for (int index = numbers.length-1; index >= 0; index--) System.out.print (numbers[index] + " "); System.out.println (); }

14. www.site.uottawa.ca/~elsaddik 14 (c) elsaddik LetterCount.java import cs1.Keyboard; public class LetterCount { public static void main (String[] args) { final int NUMCHARS = 26; int[] upper = new int[NUMCHARS]; int[] lower = new int[NUMCHARS]; char current; // the current character being processed int other = 0; // counter for non-alphabetics System.out.println ("Enter a sentence:"); String line = Keyboard.readString(); // Count the number of each letter occurence

15. www.site.uottawa.ca/~elsaddik 15 (c) elsaddik LetterCount.java for (int ch = 0; ch < line.length(); ch++) { current = line.charAt(ch); if (current >= 'A' && current <= 'Z') upper[current-'A']++; else if (current >= 'a' && current <= 'z') lower[current-'a']++; else other++; } // Print the results System.out.println (); for (int letter=0; letter < upper.length; letter++) { System.out.print ( (char) (letter + 'A') ); System.out.print (": " + upper[letter]); System.out.print ("\t\t" + (char) (letter + 'a') ); System.out.println (": " + lower[letter]); } System.out.println (); System.out.println ("Non-alphabetic characters: " + other); }

16. www.site.uottawa.ca/~elsaddik 16 (c) elsaddik Alternate Array Syntax  The brackets of the array type can be associated with the element type or with the name of the array  Therefore the following declarations are equivalent: float[] prices; float prices[];  The first format generally is more readable

17. www.site.uottawa.ca/~elsaddik 17 (c) elsaddik Initializer Lists  An initializer list can be used to instantiate and initialize an array in one step  The values are delimited by braces and separated by commas  Examples: int[] units = {147, 323, 89, 933, 540, 269, 97, 114, 298, 476}; char[] letterGrades = {'A', 'B', 'C', 'D', ’E'};

18. www.site.uottawa.ca/~elsaddik 18 (c) elsaddik Initializer Lists  Note that when an initializer list is used:  the new operator is not used  no size value is specified  The size of the array is determined by the number of items in the initializer list  An initializer list can only be used only in the declaration of an array See Primes.java (page xxx)Primes.java

19. www.site.uottawa.ca/~elsaddik 19 (c) elsaddik Primes.java public class Primes { //------------------------------------------------------- // Stores some prime numbers in an array and prints them. //------------------------------------------------------- public static void main (String[] args) { int[] primeNums = {2, 3, 5, 7, 11, 13, 17, 19}; System.out.println ("Array length: " + primeNums.length); System.out.println ("The first few prime numbers are:"); for (int scan = 0; scan < primeNums.length; scan++) System.out.print (primeNums[scan] + " "); System.out.println (); }

20. www.site.uottawa.ca/~elsaddik 20 (c) elsaddik Arrays as Parameters  An entire array can be passed as a parameter to a method  Like any other object, the reference to the array is passed, making the formal and actual parameters aliases of each other  Changing an array element within the method changes the original  An array element can be passed to a method as well, and follows the parameter passing rules of that element's type

21. www.site.uottawa.ca/~elsaddik 21 (c) elsaddik Arrays of Objects  The elements of an array can be object references  The following declaration reserves space to store 25 references to String objects String[] words = new String[25];  It does NOT create the String objects themselves  Each object stored in an array must be instantiated separately See GradeRange.java (page xxx) GradeRange.java

22. www.site.uottawa.ca/~elsaddik 22 (c) elsaddik GradeRange.java public class GradeRange { //-------------------------------------------- // Stores the possible grades and their // numeric lowest value, then prints them out. //-------------------------------------------- public static void main (String[] args) { String[] grades = {"A", "A-", "B+", "B", "B-", "C+", "C", "C-","D+", "D", "D-", "F"}; int[] cutoff = {95, 90, 87, 83, 80, 77, 73, 70, 67, 63, 60, 0}; for (int level = 0; level < cutoff.length; level++) System.out.println (grades[level] + "\t" + cutoff[level]); }

23. www.site.uottawa.ca/~elsaddik 23 (c) elsaddik Command-Line Arguments  The signature of the main method indicates that it takes an array of String objects as a parameter  These values come from command-line arguments that are provided when the interpreter is invoked  For example, the following invocation of the interpreter passes an array of three String objects into main: > java DoIt pennsylvania texas california  These strings are stored at indexes 0-2 of the parameter See NameTag.java (page xxx) NameTag.java

24. www.site.uottawa.ca/~elsaddik 24 (c) elsaddik NameTag.java public class NameTag { //-------------------------------------------------- // Prints a simple name tag using a greeting and a // name that is specified by the user. //-------------------------------------------------- public static void main (String[] args) { System.out.println (); System.out.println (" " + args[0]); System.out.println ("My name is " + args[1]); System.out.println (); }

25. www.site.uottawa.ca/~elsaddik 25 (c) elsaddik Arrays of Objects  Objects can have arrays as instance variables  Therefore, many useful structures can be created simply with arrays and objects  The software designer must determine carefully an organization of data and objects that makes sense for the situation See Tunes.java (page xxx) Tunes.java See CDCollection.java (page xxx) CDCollection.java See CD.java (page xxx) CD.java

26. www.site.uottawa.ca/~elsaddik 26 (c) elsaddik Extract from CDCollection.java (1) public class CDCollection { private CD[] collection; private int count; private int currentSize; public CDCollection () { currentSize = 100; collection = new CD[currentSize]; count = 0; } public void addCD (...) { if (count == currentSize) increaseSize(); collection[count] = new CD (...); count++; }

27. www.site.uottawa.ca/~elsaddik 27 (c) elsaddik Extract from CDCollection.java (2) private void increaseSize () { currentSize *= 2; CD[] temp = new CD[currentSize]; for (int cd = 0; cd < collection.length; cd++) temp[cd] = collection[cd]; collection = temp; }

28. www.site.uottawa.ca/~elsaddik 28 (c) elsaddik Sorting  Sorting is the process of arranging a list of items in a particular order  There must be some value on which the order is based  There are many algorithms for sorting a list of items  These algorithms vary in efficiency  We will examine two specific algorithms:  Selection Sort  Insertion Sort

29. www.site.uottawa.ca/~elsaddik 29 (c) elsaddik Selection Sort The approach of Selection Sort:  select a value and put it in its final place into the sort list  repeat for all other values In more detail:  find the smallest value in the list  switch it with the value in the first position  find the next smallest value in the list  switch it with the value in the second position  repeat until all values are in their proper places

30. www.site.uottawa.ca/~elsaddik 30 (c) elsaddik Selection Sort An example: original: 3 9 6 1 2 smallest is 1: 1 9 6 3 2 smallest is 2: 1 2 6 3 9 smallest is 3: 1 2 3 6 9 smallest is 6: 1 2 3 6 9 (smallest is 9) 1 2 3 6 9 sorted: 1 2 3 6 9 See SortGrades.java (page 289) SortGrades.java See Sorts.java (page 290) -- the selectionSort method Sorts.java

31. www.site.uottawa.ca/~elsaddik 31 (c) elsaddik Swapping  Swapping is the process of exchanging two values  Swapping requires three assignment statements temp = first; first = second; second = temp;

32. www.site.uottawa.ca/~elsaddik 32 (c) elsaddik Insertion Sort The approach of Insertion Sort:  pick any item and insert it into its proper place in a sorted sublist  repeat until all items have been inserted In more detail:  consider the first item to be a sorted sublist (of one item)  insert the second item into the sorted sublist, shifting the first item as needed to make room to insert the new addition  insert the third item into the sorted sublist (of two items), shifting items as necessary  repeat until all values are inserted into their proper positions

33. www.site.uottawa.ca/~elsaddik 33 (c) elsaddik Insertion Sort An example: original: 3 9 6 1 2 (insert 3) 3 9 6 1 2 insert 9: 3 9 6 1 2 insert 6: 3 6 9 1 2 insert 1: 1 3 6 9 2 insert 2: 1 2 3 6 9 sorted: 1 2 3 6 9 See Sorts.java (page 290) -- the insertionSort method Sorts.java 3 9 3 6 9 1 3 6 9 3 1 2 3 6 9

34. www.site.uottawa.ca/~elsaddik 34 (c) elsaddik Sorting Objects  Integers have an inherent order, but the order of a collection of objects must be defined by the person defining the class  Recall that a Java interface can be used as a type name and guarantees that a particular class implementes particular methods  We can use the Comparable interface and the CompareTo method to develop a generic sort for a set of objects See SortPhoneList.java (page xxx) SortPhoneList.java See Contact.java (page xxx) Contact.java See Sorts.java (page xxx) Sorts.java

35. www.site.uottawa.ca/~elsaddik 35 (c) elsaddik From Sorts.java public static void insertionSort (Comparable[] objects) { for (int index = 1; index < objects.length; index++) { Comparable key = objects[index]; int position = index; // shift larger values to the right while (position > 0 && objects[position-1].compareTo(key) > 0) { objects[position] = objects[position-1]; position--; } objects[position] = key; }

36. www.site.uottawa.ca/~elsaddik 36 (c) elsaddik Comparing Sorts  Both Selection and Insertion sorts are similar in efficiency  The both have outer loops that scan all elements, and inner loops that compare the value of the outer loop with almost all values in the list  Therefore approximately n 2 number of comparisons are made to sort a list of size n  We therefore say that these sorts are of order n 2  Other sorts are more efficient: order n log 2 n

37. www.site.uottawa.ca/~elsaddik 37 (c) elsaddik Two-Dimensional Arrays  A one-dimensional array stores a simple list of values  A two-dimensional array can be thought of as a table of values, with rows and columns  Because each dimension is an array of array references, the arrays within one dimension can be of different lengths  Sometimes these are called ragged arrays

38. www.site.uottawa.ca/~elsaddik 38 (c) elsaddik Two-Dimensional Arrays  A two-dimensional array element is referenced using two index values value = scores [3][6]  To be precise, a two-dimensional array in Java is an array of arrays

39. www.site.uottawa.ca/~elsaddik 39 (c) elsaddik Two-Dimensional Arrays From TwoDArray.java public static void main (String[] args) { int[][] table = new int[5][10]; // Load the table with values for (int row=0; row < table.length; row++) for (int col=0; col < table[row].length; col++) table[row][col] = row * 10 + col; // Print the table for (int row=0; row < table.length; row++) { for (int col=0; col < table[row].length; col++) System.out.print (table[row][col] + "\t"); System.out.println(); } See TwoDArray.java (page xxx) TwoDArray.java See SodaSurvey.java (page xxx)

40. www.site.uottawa.ca/~elsaddik 40 (c) elsaddik Multidimensional Arrays  An array can have many dimensions  If it has more than one dimension, it is called a multidimensional array  Each dimension subdivides the previous one into the specified number of elements  Each array dimension has its own length constant

41. www.site.uottawa.ca/~elsaddik 41 (c) elsaddik The ArrayList Class  The ArrayList class is part of the java.util package  Like an array, it can store a list of values and reference them with an index  Unlike an array, an ArrayList object grows and shrinks as needed  Items can be inserted or removed with a single method invocation  It stores references to the Object class

42. www.site.uottawa.ca/~elsaddik 42 (c) elsaddik import java.util.ArrayList; public class Beatles { public static void main (String[] args) { ArrayList band = new ArrayList(); band.add ("Paul"); band.add ("Pete"); band.add ("John"); band.add ("George"); System.out.println (band); int location = band.indexOf ("Pete"); band.remove (location); System.out.println (band); System.out.println ("At index 1: " + band.get(1)); band.add (2, "Ringo"); System.out.println (band); System.out.println ("Size of the band: " + band.size()); } See Beatles.java (page xxx) Some Methods of the ArrayList Class

43. www.site.uottawa.ca/~elsaddik 43 (c) elsaddik ArrayList Efficiency  The ArrayList class is implemented using an array.  The array expands beyond its initial capacity to accommodate additional elements  Methods manipulate the array so that indexes remain continuous as elements are added or removed

44. www.site.uottawa.ca/~elsaddik 44 (c) elsaddik Polygons and Polylines  Arrays often are helpful in graphics processing  Polygons and polylines are shapes that can be defined by values stored in arrays  A polyline is similar to a polygon except that its endpoints do not meet, and it cannot be filled See Rocket.java (page xxx) Rocket.java

45. www.site.uottawa.ca/~elsaddik 45 (c) elsaddik The Polygon Class  The Polygon class, defined in the java.awt package can be used to define and draw a polygon  Two versions of the overloaded drawPolygon and fillPolygon methods take a single Polygon object as a parameter  A Polygon object encapsulated the coordinates of the polygon

46. www.site.uottawa.ca/~elsaddik 46 (c) elsaddik Other Button Components  A check box is a button that can be toggled on or off  A check box is represented by the JCheckBox class  A change of state generates an item event  See StyleOptions.java (page xxx)StyleOptions.java  See StyleGUI.java(page xxx)StyleGUI.java

47. www.site.uottawa.ca/~elsaddik 47 (c) elsaddik The Font Class  A Font object is defined by the font name, the font style, and the font size  The style of a font can be plain, bold, italic, or bold and italic together  The itemStateChanged method of the listener responds when a check box changes state

48. www.site.uottawa.ca/~elsaddik 48 (c) elsaddik Radio Buttons  A set of radio buttons represents a set of mutually exclusive options  When a radio button from a group is selected, the other button currently on in the group is toggled off  A radio button generates an action event See QuoteOptions.java (page xxx) QuoteOptions.java See QuoteGUI.java (page xxx) QuoteGUI.java

49. www.site.uottawa.ca/~elsaddik 49 (c) elsaddik Summary Chapter 6 has focused on:  array declaration and use  passing arrays and array elements as parameters  arrays of objects  sorting elements in an array  multidimensional arrays  the ArrayList class  polygons and polylines  more button components

50. www.site.uottawa.ca/~elsaddik 50 (c) elsaddik Thank You!