C OMP 110 A RRAYS Instructor: Jason Carter

2 O UTLINE for loops Arrays

3 S TRINGS = C HAR S EQUENCES JohnF.Kennedy hello String {sequences of characters}

4 S TRING P ROCESSING Prints each character on a separate line int i = 0; while (i < s.length()) { System.out.println(s.charAt(i)); i++; }

5 D ISSECTING A L OOP int i = 0; while (i < s.length()) { System.out.println(s.charAt(i)); i++; } Loop Condition Loop Body

6 F INGER - GRAINED D ISSECTION // String s declared and initialized earlier int i = 0; while (i < s.length()) { System.out.println(s.charAt(i)); i++; } Loop Condition Loop Body Resetting Loop Variable Initializing Loop Variable for (int i=0; i<s.length(); i++) System.out.println ( s.charAt(i));

7 M EANING OF F OR L OOP for ( S1; E; S2) S3 for ( S1; E; S2) S3 for ( ; E; S2) S3 for ( ; E; S2) S3 for ( ; E;) S3 for ( ; E;) S3 for ( ;;) S3 for ( ;;) S3 S1; while (E) { S3; S2; } S1; while (E) { S3; S2; } while (E) { S3; S2; } while (E) { S3; S2; } while (E) { S3; } while (E) { S3; } S1; while ( true ) { S3; S2; } S1; while ( true ) { S3; S2; }

8 O THER P REDEFINED T YPES AS S EQUENCES IntSequence {sequences of integers} DoubleSequence {sequences of doubles} JFKFDRJCBCRRGB StringSequence {sequences of string}

9 S EQUENCES OF P ROGRAMMER -D EFINED T YPES loan1loan2loan3 LoanSequence Loan[] temperature1 TemperatureSequence Temperature [] temperature2temperature3 temperature1temperature2 Array Types Arrays Array Element

10 O THER S EQUENCES AS A RRAY T YPES int[] double[] JFKFDRJCBCRRGB String[]

11 I NITIALIZING A RRAY D ECLARATION int[] assignmentScores = {100, 98, 99, 100, 90, 80}; Array Type Array Literal Element Type Array Variable double[] gpas = {3.8, 3.1, 3.7, 3.1, 3.6, 3.9}; String[] initials = {“JFK, “FDR”, “JC”, “BC”, “RR”, “GB”}; JFKFDRJCBCRRGB

12 I NITIALIZING A RRAY D ECLARATION S YNTAX [] = {, …, } Loan [] loans = { new ALoan(100000), new AnotherLoan (100)};

13 A RRAY T YPES H AVE V ARIABLE S IZE int[] int[] assignmentScores = {100, 98, 99, 100, 90, 80}; assignmentScores = {60, 40, 50}; assignmentScores

14 A RRAY O PERATIONS String[] initials = {“JFK, “FDR”, “JC”, “BC”, “RR”, “GW”, “WW”}; JFKFDRJCBCRRGWWW initials.length6 public named constant initials[0]JFK initials[initials.length-1]WW initials[initials.length]ArrayIndexOutOfBounds Exception initials[0] = “HT” initials[initials.length] = “HT”ArrayIndexOutOfBounds Exception Array instance size fixed! HT

15 U NINITIALIZING A RRAY D ECLARATION int[] assignmentScores; assignmentScores = {60, 40, 50}; assignmentScores null

16 A RRAY E LEMENTS U NINITIALIZED int [] assignmentScores = new int [3]; assignmentScores 000

17 O BJECT A RRAY E LEMENTS U NINITIALIZED String[] initials = new String[3]; initials null

18 E XAMPLE

19 GET S TRINGS () static String[] getStrings() { System.out.println("Number of Strings:"); int numElements = Console.readInt(); System.out.println("Please enter " + numElements + " strings"); String[] strings = new String[numElements]; for ( int elementNum = 0; elementNum < numElements; elementNum++) strings[elementNum] = Console.readString(); return strings; } Variable

20 PRINT () static void print(String[] strings) { System.out.println("******************"); for ( int elementNum = 0; elementNum < strings.length; elementNum++) System.out.println(strings[elementNum]); System.out.println("******************"); } String array of arbitrary dimension

21 MAIN () public static void main(String[] args){ String[] names = getStrings(); String command = Console.readString(); while (command.length() > 0 && command.charAt(0) != ‘q’) { if (command.charAt(0) == 'p') print(names); command = Console.readString(); } Must test that length is at least 1 before accessing char at position 0 No need to test length here

22 A NOTHER E XAMPLE

23 V ARIABLE -S IZE C OLLECTION filled part unfilled part current size maximum size

24 3 James Dean Joe Doe Jane Smith sizearray V ARIABLE -S IZE C OLLECTION filled part unfilled part current size maximum size

25 V ARIABLE -S IZE C OLLECTION public class { … final static int A_MAX_SIZE = 50; String[] a = new String[A_MAX_SIZE]; int aSize = 0; … //process a for (int index = 0; index < aSize; index++) System.out.println(a[index]); … final int B_MAX_SIZE = 50; String[] b = new String[B_MAX_SIZE]; int bSize = 0; … //process b … }

26 S PECIAL T YPE public class {... AVariableSizeCollection a = new AVariableSizeCollection();... for ( int index = 0; index < a.size; index++) System.out.println(a.contents[index]); … AVariableSizeCollection b = new AVariableSizeCollection();... } public class AVariableSizeCollection { public static final int MAX_SIZE = 50; public String[] contents = new String [MAX_SIZE]; public int size = 0; } No Encapsulation Size Not Updated a.contents[a.size] = Console.readString();

27 S UPPORTING E NCAPSULATION public interface …. { public static final int MAX_SIZE = 50; public void addElement(String element); public void print(); } User-specificImplementation-specific

28 H ISTORY public interface StringHistory { public void addElement(String element); public int size(); public String elementAt( int index); }

29 I MPLEMENTING A H ISTORY public class AStringHistory implements StringHistory { public final int MAX_SIZE = 50; String[] contents = new String[MAX_SIZE]; int size = 0; public int size() { return size;} public String elementAt ( int index) { return contents[index]; } boolean isFull() { return size == MAX_SIZE; } public void addElement(String element) { if (isFull()) System.out.println("Adding item to a full history"); else { contents[size] = element; size++; }

30 U SING A H ISTORY public static void main(String[] args) { StringHistory names = new AStringHistory(); while ( true ) { String input = Console.readString(); if (input.length() > 0) if (input.charAt(0) == 'q') break ; else if (input.charAt(0) == 'p' ) print(names); else names.addElement(input); } Exits from the loop

31 P RINTING A H ISTORY static void print(StringHistory strings) { System.out.println("******************"); for ( int elementNum = 0; elementNum < strings.size(); elementNum++) System.out.println(strings.elementAt(elementNum)); System.out.println("******************"); }

32 AP OINT H ISTORY Variable-sized Collection History Elements accessed by ObjectEditor Conventions for exporting elements

33 C ONVENTIONS FOR V ARIABLE -S IZED C OLLECTION public interface PointHistory { public void addElement ( int x, int y); public Point elementAt ( int index); public int size(); } Read Methods Write Method Arbitrary Type

34

35 E XTRA S LIDES

36 loans null loans null ALoan(10000) AnotherLoan(100) Loan[]Loan