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Review 2 Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Constants: final • A final variable is a constant • Once its value has been set, it cannot be changed • Named constants make programs easier to read and maintain • Convention: use all-uppercase names for constants final double QUARTER_VALUE = 0.25; final double DIME_VALUE = 0.1; final double NICKEL_VALUE = 0.05; final double PENNY_VALUE = 0.01; payment = dollars + quarters * QUARTER_VALUE + dimes * DIME_VALUE + nickels * NICKEL_VALUE + pennies * PENNY_VALUE; Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Constants: static final • If constant values are needed in several methods, declare them together with the instance fields of a class and tag them as static and final • Give static final constants public access to enable other classes to use them public class Math { . . . public static final double E = 2.7182818284590452354; public static final double PI = 3.14159265358979323846; } double circumference = Math.PI * diameter; Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Syntax 4.2 Constant Definition In a method: final typeName variableName = expression; In a class: accessSpecifier static final typeName variableName = expression; Example: final double NICKEL_VALUE = 0.05; public static final double LITERS_PER_GALLON = 3.785; Purpose: To define a constant in a method or a class. Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Assignment, Increment, and Decrement • Assignment is not the same as mathematical equality: items = items + 1; • items++ is the same as items = items + 1 • items-- subtracts 1 from items Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Assignment, Increment, and Decrement Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Arithmetic Operations • / is the division operator • If both arguments are integers, the result is an integer. The remainder is discarded • 7.0 / 4 yields 1.75 7 / 4 yields 1 • Get the remainder with % (pronounced "modulo") 7 % 4 is 3 Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Arithmetic Operations final final final final int int int int PENNIES_PER_NICKEL = 5; PENNIES_PER_DIME = 10; PENNIES_PER_QUARTER = 25; PENNIES_PER_DOLLAR = 100; // Compute total value in pennies int total = dollars * PENNIES_PER_DOLLAR + quarters * PENNIES_PER_QUARTER + nickels * PENNIES_PER_NICKEL + dimes * PENNIES_PER_DIME + pennies; // Use integer division to convert to dollars, cents int dollars = total / PENNIES_PER_DOLLAR; int cents = total % PENNIES_PER_DOLLAR; Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. The Math class • Math class: contains methods like sqrt and pow • To compute xn, you write Math.pow(x, n) • However, to compute x2 it is significantly more efficient simply to compute x * x • To take the square root of a number, use the Math.sqrt; for example, Math.sqrt(x) • In Java, can be represented as (-b + Math.sqrt(b * b - 4 * a * c)) / (2 * a) Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Self Check 4.8 What is the value of 1729 / 100? Of 1729 % 100? Answer: 17 and 29 Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Syntax 4.3 Static Method Call ClassName.methodName(parameters) Example: Math.sqrt(4) Purpose: To invoke a static method (a method that does not operate on an object) and supply its parameters. Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Self Check 4.11 Why can't you call x.pow(y) to compute xy? Answer: x is a number, not an object, and you cannot invoke methods on numbers. Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Self Check 4.12 Is the call System.out.println(4) a static method call? Answer: No – the println method is called on the object System.out. Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Strings • A string is a sequence of characters • Strings are objects of the String class • String constants: "Hello, World!" • String variables: String message = "Hello, World!"; • String length: int n = message.length(); • Empty string: "" Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Concatenation • Use the + operator: String name = "Dave"; String message = "Hello, " + name; // message is "Hello, Dave" • If one of the arguments of the + operator is a string, the other is converted to a string String a = "Agent"; int n = 7; String bond = a + n; // bond is "Agent7" Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Concatenation in Print Statements • Useful to reduce the number of System.out.print instructions System.out.print("The total is "); System.out.println(total); versus System.out.println("The total is " + total); Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Substrings • String greeting = "Hello, World!"; String sub = greeting.substring(0, 5); // sub is "Hello" • Supply start and “past the end” position • First position is at 0 Continued Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Substrings (cont.) Substring length is “past the end” - start Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Self Check 4.13 Assuming the String variable s holds the value "Agent", what is the effect of the assignment s = s + s.length()? Answer: s is set to the string Agent5 Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Reading Input • System.in has minimal set of features–it can only read one byte at a time • In Java 5.0, Scanner class was added to read keyboard input in a convenient manner • Scanner in = new Scanner(System.in); System.out.print("Enter quantity:"); int quantity = in.nextInt(); • nextDouble reads a double • nextLine reads a line (until user hits Enter) • nextWord reads a word (until any white space) Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. ch04/cashregister/CashRegisterSimulator.java 01: import java.util.Scanner; 02: 03: /** 04: This program simulates a transaction in which a user pays for an item 05: and receives change. 06: */ 07: public class CashRegisterSimulator 08: { 09: public static void main(String[] args) 10: { 11: Scanner in = new Scanner(System.in); 12: 13: CashRegister register = new CashRegister(); 14: 15: System.out.print("Enter price: "); 16: double price = in.nextDouble(); 17: register.recordPurchase(price); 18: 19: System.out.print("Enter dollars: "); 20: int dollars = in.nextInt(); Continued Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. ch04/cashregister/CashRegisterSimulator.java (cont.) Output: Enter price: 7.55 Enter dollars: 10 Enter quarters: 2 Enter dimes: 1 Enter nickels: 0 Enter pennies: 0 Your change: is 3.05 Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. The if Statement • The if statement lets a program carry out different actions depending on a condition If (amount <= balance) balance = balance – amount; Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. The if/else Statement If (amount <= balance) balance = balance – amount; else balance = balance – OVERDRAFT_PENALTY Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Statement Types • Simple statement balance = balance - amount; • Compound statement if (balance >= amount) balance = balance - amount; Also while, for, etc. (loop statements – Chapter 6) • Block statement { double newBalance = balance - amount; balance = newBalance; } Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Syntax 5.1 The if Statement if(condition) statement if (condition) statement1 else Example: if (amount balance if (amount balance else <= balance) = balance - amount; <= balance) = balance - amount; Purpose: To execute a statement when a condition is true or false. Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Syntax 5.2 Block Statement { statement1 statement2 . . . } Example: { double newBalance = balance - amount; balance = newBalance; } Purpose: To group several statements together to form a single statement. Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Self Check 5.2 What is logically wrong with the statement if (amount <= balance) newBalance = balance - amount; balance = newBalance; and how do you fix it? Answer: Only the first assignment statement is part of the if statement. Use braces to group both assignment statements into a block statement. Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Comparing Strings • Don't use == for strings! if (input == "Y") // WRONG!!! • Use equals method: if (input.equals("Y")) • == tests identity, equals tests equal contents • Case insensitive test ("Y" or "y") if (input.equalsIgnoreCase("Y")) • s.compareTo(t) < 0 means: s comes before t in the dictionary Continued Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Comparing Strings (cont.) • "car" comes before "cargo" • All uppercase letters come before lowercase: "Hello" comes before "car" Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Nested Branches (cont.) Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Using Boolean Expressions: The Boolean Operators • && and • || or •! not • if (0 < amount && amount < 1000) . . . • if (input.equals("S") || input.equals("M")) . . . Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. && and || Operators Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Truth Tables A B A && B true true true true false false false Any false A B A || B true Any true false true true false false false A !A true false false true Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. while Loops • Executes a block of code repeatedly • A condition controls how often the loop is executed while (condition) statement • Most commonly, the statement is a block statement (set of statements delimited by { }) Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Calculating the Growth of an Investment • Invest $10,000, 5% interest, compounded annually Year Balance 0 $10,000 1 $10,500 2 $11,025 3 $11,576.25 4 $12,155.06 5 $12,762.82 Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. while Loop Flowchart Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Syntax 6.1 The while Statement while (condition) statement Example: while (balance < targetBalance) { years++; double interest = balance * rate / 100; balance = balance + interest; } Purpose: To repeatedly execute a statement as long as a condition is true. Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Common Error: Infinite Loops • int years = 0; while (years < 20) { double interest = balance * rate / 100; balance = balance + interest; } • int years = 20; while (years > 0) { years++; // Oops, should have been years– double interest = balance * rate / 100; balance = balance + interest; } • Loops run forever – must kill program Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. do Loops • Executes loop body at least once: do statement while (condition); • Example: Validate input double value; do { System.out.print("Please enter a positive number: "); value = in.nextDouble(); } while (value <= 0); Continued Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. do Loops (cont.) • Alternative: boolean done = false; while (!done) { System.out.print("Please enter a positive number: "); value = in.nextDouble(); if (value > 0) done = true; } Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. do Loop Flowchart Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Spaghetti Code Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. for Loops • for (initialization; condition; update) statement • Example: for (int i = 1; i <= n; i++) { double interest = balance * rate / 100; balance = balance + interest; } • Equivalent to initialization; while (condition) { statement; update; } Continued Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. for Loops (cont.) • Other examples: for (years = n; years > 0; years--) . . . for (x = -10; x <= 10; x = x + 0.5) . . . Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. for Loop Flowchart Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Syntax 6.2 The for Statement for (initialization; condition; update) statement Example: for (int i = 1; i <= n; i++) { double interest = balance * rate / 100; balance = balance + interest; } Purpose: To execute an initialization, then keep executing a statement and updating an expression while a condition is true. Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Processing Sentinel Values • Sentinel value: Can be used for indicating the end of a data set • 0 or -1 make poor sentinels; better use Q System.out.print("Enter value, Q to quit: "); String input = in.next(); if (input.equalsIgnoreCase("Q")) We are done else { double x = Double.parseDouble(input); . . . } Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Loop and a half • Sometimes termination condition of a loop can only be evaluated in the middle of the loop • Then, introduce a boolean variable to control the loop: boolean done = false; while (!done) { Print prompt String input = read input; if (end of input indicated) done = true; else { Process input } } Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Random Numbers and Simulations • In a simulation, you repeatedly generate random numbers and use them to simulate an activity • Random number generator Random generator = new Random(); int n = generator.nextInt(a); // 0 < = n < a double x = generator.nextDouble(); // 0 <= x < 1 • Throw die (random number between 1 and 6) int d = 1 + generator.nextInt(6); Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. ch06/random1/Die.java 01: 02: 03: 04: 05: 06: 07: 08: 09: 10: 11: 12: 13: 14: 15: 16: 17: 18: 19: 20: 21: 22: import java.util.Random; /** This class models a die that, when cast, lands on a random face. */ public class Die { /** Constructs a die with a given number of sides. @param s the number of sides, e.g. 6 for a normal die */ public Die(int s) { sides = s; generator = new Random(); } /** Simulates a throw of the die @return the face of the die Continued */ Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. ch06/random1/Die.java (cont.) 23: 24: 25: 26: 27: 28: 29: 30: } public int cast() { return 1 + generator.nextInt(sides); } private Random generator; private int sides; Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. ch06/random1/DieSimulator.java 01: 02: 03: 04: 05: 06: 07: 08: 09: 10: 11: 12: 13: 14: 15: 16: 17: /** This program simulates casting a die ten times. */ public class DieSimulator { public static void main(String[] args) { Die d = new Die(6); final int TRIES = 10; for (int i = 1; i <= TRIES; i++) { int n = d.cast(); System.out.print(n + " "); } System.out.println(); } } Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. ch06/random1/DieSimulator.java (cont.) Output: 6 5 6 3 2 6 3 4 4 1 Second Run: 3 2 2 1 6 5 3 4 1 2 Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Self Check 6.9 How do you use a random number generator to simulate the toss of a coin? Answer: int n = generator.nextInt(2); // 0 = heads, 1 = tails Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Using a Debugger • Debugger = program to run your program and analyze its run-time behavior • A debugger lets you stop and restart your program, see contents of variables, and step through it • The larger your programs, the harder to debug them simply by inserting print commands • Debuggers can be part of your IDE (e.g. Eclipse, BlueJ) or separate programs (e.g. JSwat) • Three key concepts: • Breakpoints • Single-stepping • Inspecting variables Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Debugging • Execution is suspended whenever a breakpoint is reached • In a debugger, a program runs at full speed until it reaches a breakpoint • When execution stops you can: • Inspect variables • Step through the program a line at a time • Or, continue running the program at full speed until it reaches the next breakpoint • When program terminates, debugger stops as well • Breakpoints stay active until you remove them • Two variations of single-step command: • Step Over: skips method calls • Step Into: steps inside method calls Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Single-step Example Current line: String input = in.next(); Word w = new Word(input); int syllables = w.countSyllables(); System.out.println("Syllables in " + input + ": " + syllables); When you step over method calls, you get to the next line: String input = in.next(); Word w = new Word(input); int syllables = w.countSyllables(); System.out.println("Syllables in " + input + ": " + syllables); Continued Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Single-step Example (cont.) However, if you step into method calls, you enter the first line of the countSyllables method public { int int . . } int countSyllables() count = 0; end = text.length() - 1; . Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Self Check 6.11 In the debugger, you are reaching a call to System.out.println. Should you step into the method or step over it? Answer: You should step over it because you are not interested in debugging the internals of the println method. Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Self Check 6.12 In the debugger, you are reaching the beginning of a long method with a couple of loops inside. You want to find out the return value that is computed at the end of the method. Should you set a breakpoint, or should you step through the method? Answer: You should set a breakpoint. Stepping through loops can be tedious. Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. ch06/debugger/Word.java 01: 02: 03: 04: 05: 06: 07: 08: 09: 10: 11: 12: 13: 14: 15: 16: 17: 18: 19: 20: 21: /** This class describes words in a document. */ public class Word { /** Constructs a word by removing leading and trailing nonletter characters, such as punctuation marks. @param s the input string */ public Word(String s) { int i = 0; while (i < s.length() && !Character.isLetter(s.charAt(i))) i++; int j = s.length() - 1; while (j > i && !Character.isLetter(s.charAt(j))) j--; text = s.substring(i, j); } Continued Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. ch06/debugger/Word.java (cont.) 22: 23: 24: 25: 26: 27: 28: 29: 30: 31: 32: 33: 34: 35: 36: 37: 38: 39: 40: 41: /** Returns the text of the word, after removal of the leading and trailing non-letter characters. @return the text of the word */ public String getText() { return text; } /** Counts the syllables in the word. @return the syllable count */ public int countSyllables() { int count = 0; int end = text.length() - 1; if (end < 0) return 0; // The empty string has no syllables Continued Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. ch06/debugger/Word.java (cont.) 42: 43: 44: 46: 47: 48: 49: 50: 51: 52: 53: 54: 55: 56: 57: 58: 59: 60: 61: 62: // An e at the end of the word doesn't count as a vowel char ch = Character.toLowerCase(text.charAt(end)); if (ch == 'e') end--; boolean insideVowelGroup = false; for (int i = 0; i <= end; i++) { ch = Character.toLowerCase(text.charAt(i)); String vowels = "aeiouy"; if (vowels.indexOf(ch) >= 0) { // ch is a vowel if (!insideVowelGroup) { // Start of new vowel group count++; insideVowelGroup = true; } } } Continued Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. ch06/debugger/Word.java (cont.) 63: 64: 65: 66: 67: 68: 69: 70: 71: } // Every word has at least one syllable if (count == 0) count = 1; return count; } private String text; Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. ch06/debugger/SyllableCounter.java 01: 02: 03: 04: 05: 06: 07: 08: 09: 10: 11: 12: 13: 14: 15: 16: 17: 18: 19: 20: 21: 22: import java.util.Scanner; /** This program counts the syllables of all words in a sentence. */ public class SyllableCounter { public static void main(String[] args) { Scanner in = new Scanner(System.in); System.out.println("Enter a sentence ending in a period."); String input; do { input = in.next(); Word w = new Word(input); int syllables = w.countSyllables(); System.out.println("Syllables in " + input + ": " + syllables); Continued } Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. ch06/debugger/SyllableCounter.java (cont.) 23: 24: 25: } while (!input.endsWith(".")); } Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Debug the Program • Buggy output (for input "hello yellow peach."): Syllables in hello: 1 Syllables in yellow: 1 Syllables in peach.: 1 • Set breakpoint in first line of countSyllables of Word class • Start program, supply input. Program stops at breakpoint • Method checks if final letter is 'e' Continued Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Debug the Program (cont.) • Check if this works: step to line where check is made and inspect variable ch • Should contain final letter but contains 'l' Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. More Problems Found • end is set to 3, not 4 • text contains "hell", not "hello" • No wonder countSyllables returns 1 Continued Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. More Problems Found (cont.) • Culprit is elsewhere • Can't go back in time • Restart and set breakpoint in Word constructor Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Debugging the Word Constructor • Supply "hello" input again • Break past the end of second loop in constructor • Inspect i and j • They are 0 and 4 – makes sense since the input consists of letters • Why is text set to "hell"? • Off-by-one error: Second parameter of substring is the first position not to include text = substring(i, j); should be text = substring(i, j + 1); Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Debugging the Word Constructor Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Another Error • Fix the error • Recompile • Test again: Syllables in hello: 1 Syllables in yellow: 1 Syllables in peach.: 1 • Oh no, it's still not right • Start debugger • Erase all old breakpoints and set a breakpoint in countSyllables method • Supply input "hello." Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Debugging countSyllables (again) Break in the beginning of countSyllables. Then, single-step through loop boolean insideVowelGroup = false; for (int i = 0; i <= end; i++) { ch = Character.toLowerCase(text.charAt(i)); if ("aeiouy".indexOf(ch) >= 0) { // ch is a vowel if (!insideVowelGroup) { // Start of new vowel group count++; insideVowelGroup = true; } } } Continued Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Debugging countSyllables (again) • First iteration ('h'): skips test for vowel • Second iteration ('e'): passes test, increments count • Third iteration ('l'): skips test • Fifth iteration ('o'): passes test, but second if is skipped, and count is not incremented Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Fixing the Bug • insideVowelGroup was never reset to false • Fix if ("aeiouy".indexOf(ch) >= 0) { . . . } else insideVowelGroup = false; • Retest: All test cases pass Syllables in hello: 2 Syllables in yellow: 2 Syllables in peach.: 1 • Is the program now bug-free? The debugger can't answer that. Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Self Check 6.13 What caused the first error that was found in this debugging session? Answer: The programmer misunderstood the second parameter of the substring method–it is the index of the first character not to be included in the substring. Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. Self Check 6.14 What caused the second error? How was it detected? Answer: The second error was caused by failing to reset insideVowelGroup to false at the end of a vowel group. It was detected by tracing through the loop and noticing that the loop didn't enter the conditional statement that increments the vowel count. Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved. The First Bug Big Java by Cay Horstmann Copyright © 2008 by John Wiley & Sons. All rights reserved.