Comp 114 Foundations of Programming Instructor: Prasun Dewan (Pr  sün Divän)

Hello World

Topics Assumed & Reviewed Types –int, double, char, String Variables, constants, expressions Arrays Assignment, conditionals, loops Procedures/Functions/Subroutines/Methods Parameters/arguments

Hello World package warmup; public class AHelloWorldGreeter { public static void main (String[] args) { System.out.println ("Hello World"); } Array of user-supplied arguments main header directory/library

Main Arguments user-supplied argument

Main Arguments package warmup; public class AnArgPrinter { public static void main (String[] args) { System.out.println (args[0]); } First argument args[0] args[1] Second argument...

Main Arguments user- supples no argument package warmup; public class AnArgPrinter { public static void main (String[] args) { System.out.println (args[0]); } program refers to argument array element exception!

Safe Arg Printer

Safe Arg Printer (edit in class) package warmup; public class ASafeArgPrinter { public static void main (String[] args) { //args.length gives number of elements in args array. }

Safe Arg Printer package warmup; public class ASafeArgPrinter { public static void main (String[] args) { if (args.length = = 1) System.out.println (args[0]); else { System.out.println("Illegal no of arguments:" + args.length + ". Terminating program"); System.exit(-1); }

If-else Statement if ( ) else

If-Else Statement true false

Compound Statement if (args.length = = 1) System.out.println (args[0]); else { System.out.println("Illegal no of arguments:" + args.length + ". Terminating program"); System.exit(-1); }

Nested if-else public static char toLetterGrade (int score) { if (score >= A_CUTOFF) return 'A'; else if (score >= B_CUTOFF) return 'B'; else if (score >= C_CUTOFF) return 'C'; else if (score >= D_CUTOFF) return 'D'; else return 'F'; }

Nested If-Else if (score >= A_CUTOFF) return 'A'; else if (score >= B_CUTOFF) return 'B'; else if (score >= C_CUTOFF) return 'C'; else if (score >= D_CUTOFF) return 'D'; else return 'F';

Nested If-Else

If Statement if (args.length = = 1) System.out.println (”args[0]”); if ( ) ;

Printing Multiple Arguments

Printing Multiple Arguments (edit in class) package warmup; public class AnArgsPrinter { public static void main(String[] args){ }

Printing Multiple Arguments package warmup; public class AnArgsPrinter { public static void main(String[] args){ int argNo = 0; while (argNo < args.length) { System.out.println(args[argNo]); argNo++; }

If Vs While Statement if ( ) ; while ( ) ;

if Statement true false

while Statement true false

while loop true false

Scanning Problem

char Constants char {letters, digits, operators...} ‘a’ ‘A‘ ‘1’ ‘< ‘ ‘’ 16 bits ‘ ‘’’ ‘\’’ Escape sequence ‘\n’ newline ‘ ‘\’ ‘\\’

Useful Escape Sequences

Ordering Characters ‘’‘a’…. position in ordered character list ordinal number (integer code) ….

Ordering Characters ‘’‘a’…. ‘b’‘c’‘z’…. ‘’‘A’…. ‘B’‘C’‘Z’…. ‘’‘0’…. ‘1’‘2’‘3’…. ‘a’ > ‘b’  false ‘B’ > ‘A’  true ‘4’ > ‘0’  true ‘0’ > ‘’  true ‘a’ > ‘A’  ??? ‘a’ > ‘0’  ???

Converting between Characters and their Ordinal Numbers (int) ‘a’  ordinal number of ’a’ (char) 55  character whose ordinal number is 55 (int) ‘’  0 0 (char) 0  ‘’ (int) ‘d’  ??? (char) 1  ??? (char) -1 (int) ‘c’ - (int) ‘a’  2 2 ‘c’ - ‘a’  2 2 Implicit cast to wider type (char) (‘c’ - 2)  ‘a’ (char) (‘A’ + 2)  ‘C’ (char) (‘C’ - ‘A’ + ‘a’)  ‘c’

String constants String{sequences of characters} “hello” “123” “hello 123” “a” variable size ‘a’ “” “hello\n\n123” “\”“\\” Object Type

Accessing String Components String s = “hello world”; s[0] s[1]... s.charAt(0)  ‘h’ s.charAt(1)  ‘e’ s.charAt(-1) s.charAt(11) StringIndexBounds exceptiom index s.length()  11 “ ”.length()  1 1  0 0

Accessing SubString “hello world”.substring(4,7)  s.charAt(beginIndex).. s.charAt(endIndex-1) s.substring(beginIndex, endIndex)  “o w” “hello world”.substring(4,4)  “” “hello world”.substring(7,4) StringIndexBounds exceptiom

String Processing int i = 0; while (i < s.length()) { System.out.println (s.charAt(i)); i++; } prints each character on separate line

Dissecting a Loop int i = 0; while (i < s.length()) { System.out.println (s.charAt(i)); i++; } loop condition loop body

Finer-grained Dissection int i = 0; while (i < s.length()) { System.out.println (s.charAt(i)); i++; } loop condition real body Resetting loop variable initalizing loop variables for (int i=0; i<s.length(); i++) System.out.println(s.charAt(i));

Meaning of For Loop S1; while ( E) { S3; S2; } for (S1; E; S2) S3 for (; E; S2) S3 while ( E) { S3; S2; } for (; E; ) S3 while ( E) { S3; } for (; ; ) S3 while ( true) S3;

Scanning Problem

Scanning Scanning image for text. Scanning frequencies for radio stations. Finding words in a sentence Finding identifiers, operators, in a program

Scanning JohnF.Kenndye token Input stream Token Stream token

Algorithm JohnF.Kenndye marker 0 Output: J

Algorithm JohnF.Kenndye marker 1 Output: J String inputLine

Algorithm JohnF.Kenndye marker 2 Output: J

Algorithm JohnF.Kenndye marker 5 Output: JF

Algorithm JohnF.Kenndye marker 6 Output: JF

Algorithm JohnF.Kenndye marker 8 Output: JFK

Algorithm JohnF.Kenndye marker 9 Output: JFK

Algorithm JohnF.Kenndye marker 14 Output: JFK

Solution (edit in class) package warmup; public class AnUpperCasePrinter { public static void main(String[] args){ }

Solution package warmup; public class AnUpperCasePrinter { public static void main(String[] args){ if (args.length != 1) { System.out.println("Illegal number of arguments:" + args.length + ". Terminating program."); System.exit(-1); } System.out.println("Upper Case Letters:"); int index = 0; while (index < args[0].length()) { if (isUpperCase(args[0].charAt(index))) System.out.print(args[0].charAt(index)); index++; } System.out.println(); } public static boolean isUpperCase(char c) { return (c >= 'A') && (c <= 'Z'); }

Printing Scanned Characters Backwards

Strings = Char Sequences JohnF.Kenndye hello String{sequences of characters} 143l0

Other Sequences as Predefined Types {sequences of integers} 80 JFKFDR {sequence of Strings} JCBCRRGB {sequences of doubles} IntSequence DoubleSequence StringSequence

Other Sequences as Array Types {sequences of integers} 80 {sequence of strings} {sequences of doubles} int[] double[] String[] JFKFDRJCBCRRGB

Initializing Array Declarations int[] assignmentScores = {100, 98, 99, 100, 90 80}; double[] gpas = {3.8, 3.1, 3.7, 3.1, 3.6, 3.9};String[] initials = {“JFK”, “FDR”, “JC”, “BC”, “GW”, “WW”}; JFKFDRJCBCGWWW assignmentScores Array Type Element Type Array Literal Array Variable

Array Operations String[] initials = {“JFK”, “FDR”, “JC”, “BC”, “GW”, “WW”}; JFKFDRJCBCGWWW initials.length  6 initials[0] initials[initials.length - 1] initials[initials.length]  ArrayIndexOutOfBoundsException public named constant initials[0] = “HT” HT initials[initials.length] = “HT”  ArrayIndexOutOfBoundsException Array Instance Size Fixed

Array Types have Variable-Size int[] int[] assignmentScores = {100, 98, 99, 100, 99, 80}; assignmentScores assignmentScores = {60, 40, 50}; assignmentScores

Uninitializing Array Declaration int[] assignmentScores; assignmentScores null assignmentScores = {60, 40, 50}; assignmentScores

Array Elements Uninitialized int[] assignmentScores = new int[3]; assignmentScores 000

Printing Scanned Characters Backwards

Variable-Size Collection filled part unfilled part current size maximum size

3 J F K sizearray Variable-Size Collection filled part unfilled part current size maximum size

Variable-Size Collection static final int MAX_CHARS = 7; static char[] upperCaseLetters = new char[MAX_CHARS]; static int numberOfUpperCaseLetters = 0;

Solution package warmup; public class AReverseUpperCasePrinter { static final int MAX_CHARS = 5; static char[] upperCaseLetters = new char[MAX_CHARS]; static int numberOfUpperCaseLetters = 0; public static void main(String[] args){ if (args.length != 1) { System.out.println("Illegal number of arguments:" + args.length + ". Terminating program."); System.exit(-1); } int index = 0; System.out.println("Upper Case Letters:"); while (index < args[0].length()) { if (isUpperCase(args[0].charAt(index))) { System.out.print(args[0].charAt(index)); storeChar(args[0].charAt(index)); } index++; } System.out.println(); printReverse(); }

Solution (contd.) public static void storeChar(char c) { if (numberOfUpperCaseLetters == MAX_CHARS) { System.out.println("Too many upper case letters. Terminating program. "); System.exit(-1); } upperCaseLetters[numberOfUpperCaseLetters] = c; numberOfUpperCaseLetters++; } public static void printReverse() { System.out.println("Upper Case Letters in Reverse:"); for (int index =numberOfUpperCaseLetters - 1; index >= 0; index--) { System.out.print(upperCaseLetters[index]); }

Creating JBuilder Project

Adding a Class

Editing the Class

Saving the Class

Running the Class

Viewing the Results

Running with arguments

Setting a break point

Running in debugging mode

Stopping at breakpoint

Examining the call stack

Navigating main parameters

Stepping to next statement (F8)

Stepping to next statement

Variable values

Stepping Over

Stepping Into (F9)

Stepping Out

Resuming normal execution

Program termination