1. Syllabus (1) WeekChapters 1Introduction to the course, basic java language programming concepts: Primitive Data Types and Operations 1, 2 2Methods, Control Statements, Arrays4, 3, 5 3Object Oriented Programming: Objects and Classes6 4Data Member, Member Method, Static and final members. Constructor 6 5Visibility Modifiers, Acessors, and Mutators6 6Inheritance, Object Class8 7Review + Array of Objects, Some handy Java Classes; Arrays, String, StringBuffer, StringTokenizer, Vector 7 8MIDTERM Methods, Control Statements, Arrays

2. Syllabus (2) 9 Array of Objects, Some handy Java Classes; Arrays, String, StringBuffer, StringTokenizer, Vector 7 10 Concrete class, Abstract Class, Interface 9 11 Polymorphism 8 12 Error Handling, Exception Classes and Custom Java Exceptions 15 13 GUI Programming, event driven programming, components and containers, AWT (Abstract Window Toolkit), swing 11, 12, 13 14 GUI Programming, event driven programming, components and containers, AWT (Abstract Window Toolkit), swing 11, 12, 13 15 GUI Programming, Applet 14 16 Review 17 FINAL

3. Chapter 4 Methods F Introducing Methods –Benefits of methods, Declaring Methods, and Calling Methods F Passing Parameters –Pass by Value F Overloading Methods –Ambiguous Invocation F Scope of Local Variables F Method Abstraction  The Math Class F Case Studies F Recursion (Optional)

4. Introducing Methods Method Structure A method is a collection of statements that are grouped together to perform an operation.

5. Introducing Methods, cont. parameter profile refers to the type, order, and number of the parameters of a method. method signature is the combination of the method name and the parameter profiles. The parameters defined in the method header are known as formal parameters. When a method is invoked, its formal parameters are replaced by variables or data, which are referred to as actual parameters.

6. Declaring Methods public static int max(int num1, int num2) { if (num1 > num2) return num1; else return num2; }

7. Calling Methods Example 4.1 Testing the max method This program demonstrates calling a method max to return the largest of the int values TestMax

8. Calling Methods, cont.

10. CAUTION A return statement is required for a nonvoid method. The following method is logically correct, but it has a compilation error, because the Java compiler thinks it possible that this method does not return any value. public static int xMethod(int n) { if (n > 0) return 1; else if (n == 0) return 0; else if (n < 0) return –1; } To fix this problem, delete if (n<0) in the code.

11. Passing Parameters public static void nPrintln(String message, int n) { for (int i = 0; i < n; i++) System.out.println(message); }

12. Pass by Value Example 4.2 Testing Pass by value This program demonstrates passing values to the methods. TestPassByValue

13. Pass by Value, cont.

14. Overloading Methods Example 4.3 Overloading the max Method public static double max(double num1, double num2) { if (num1 > num2) return num1; else return num2; } TestMethodOverloading

15. Ambiguous Invocation Sometimes there may be two or more possible matches for an invocation of a method, but the compiler cannot determine the most specific match. This is referred to as ambiguous invocation. Ambiguous invocation is a compilation error.

16. Ambiguous Invocation public class AmbiguousOverloading { public static void main(String[] args) { System.out.println(max(1, 2)); } public static double max(int num1, double num2) { if (num1 > num2) return num1; else return num2; } public static double max(double num1, int num2) { if (num1 > num2) return num1; else return num2; }

17. Scope of Local Variables A local variable: a variable defined inside a method. Scope: the part of the program where the variable can be referenced. The scope of a local variable starts from its declaration and continues to the end of the block that contains the variable. A local variable must be declared before it can be used.

18. Scope of Local Variables, cont. You can declare a local variable with the same name multiple times in different non- nesting blocks in a method, but you cannot declare a local variable twice in nested blocks.

19. Scope of Local Variables, cont.

20. // Fine with no errors public static void correctMethod() { int x = 1; int y = 1; // i is declared for (int i = 1; i < 10; i++) { x += i; } // i is declared again for (int i = 1; i < 10; i++) { y += i; }

21. Scope of Local Variables, cont. // With no errors public static void incorrectMethod() { int x = 1; int y = 1; for (int i = 1; i < 10; i++) { int x = 0; x += i; }

22. Method Abstraction You can think of the method body as a black box that contains the detailed implementation for the method.

23. Benefits of Methods Write a method once and reuse it anywhere. Information hiding. Hide the implementation from the user. Reduce complexity.

24. The Math Class F Class constants: –PI –E F Class methods: –Trigonometric Methods –Exponent Methods –Rounding Methods –min, max, abs, and random Methods

25. Trigonometric Methods F sin(double a) F cos(double a) F tan(double a) F acos(double a) F asin(double a) F atan(double a)

26. Exponent Methods  exp(double a) Returns e raised to the power of a.  log(double a) Returns the natural logarithm of a.  pow(double a, double b) Returns a raised to the power of b.  sqrt(double a) Returns the square root of a.

27. Rounding Methods  double ceil(double x) x rounded up to its nearest integer. This integer is returned as a double value.  double floor(double x) x is rounded down to its nearest integer. This integer is returned as a double value.  double rint(double x) x is rounded to its nearest integer. If x is equally close to two integers, the even one is returned as a double.  int round(float x) Return (int)Math.floor(x+0.5).  long round(double x) Return (long)Math.floor(x+0.5).

28. min, max, abs, and random  max(a, b) and min(a, b) Returns the maximum or minimum of two parameters.  abs(a) Returns the absolute value of the parameter.  random() Returns a random double value in the range [0.0, 1.0).

29. Example 4.4 Computing Taxes with Methods Example 3.1, “Computing Taxes,” uses if statements to check the filing status and computes the tax based on the filing status. Simplify Example 3.1 using methods. Each filing status has six brackets. The code for computing taxes is nearly same for each filing status except that each filing status has different bracket ranges. For example, the single filer status has six brackets [0, 6000], (6000, 27950], (27950, 67700], (67700, 141250], (141250, 307050], (307050,  ), and the married file jointly status has six brackets [0, 12000], (12000, 46700], (46700, 112850], (112850, 171950], (171950, 307050], (307050,  ).

30. Example 4.4 Computing Taxes with Methods The first bracket of each filing status is taxed at 10%, the second 15%, the third 27%, the fourth 30%, the fifth 35%, and the sixth 38.6%. So you can write a method with the brackets as arguments to compute the tax for the filing status. The signature of the method is: public static double computeTax(double income, int r1, int r2, int r3, int r4, int r5) ComputeTaxWithMethod

31. Example 4.5 Computing Mean and Standard Deviation Generate 10 random numbers and compute the mean and standard deviation ComputeMeanDeviation

32. Example 4.6 Obtaining Random Characters Write the methods for generating random characters. The program uses these methods to generate 175 random characters between ‘!' and ‘~' and displays 25 characters per line. To find out the characters between ‘!' and ‘~', see Appendix B, “The ASCII Character Set.” RandomCharacter

33. Example 4.6 Obtaining Random Characters, cont. Appendix B: ASCII Character Set

34. Case Studies Example 4.7 Displaying Calendars The program reads in the month and year and displays the calendar for a given month of the year. PrintCalendar

35. Design Diagram

36. Recursion (Optional) Example 4.8 Computing Factorial factorial(0) = 1; factorial(n) = n*factorial(n-1); Factorial(3) = 3 * factorial(2) = 3 * (2 * factorial(1)) = 3 * ( 2 * (1 * factorial(0))) = 3 * ( 2 * ( 1 * 1))) = 3 * ( 2 * 1) = 3 * 2 = 6 ComputeFactorial

37. Example 4.8 Computing Factorial, cont.

39. Fibonacci Numbers Example 4.8 Computing Finonacci Numbers 0 1 1 2 3 5 8 13 21 34 55 89… f0 f1 fib(0) = 0; fib(1) = 1; fib(n) = fib(n-1) + fib(n-2); n>=2 fib(3) = fib(2) + fib(1) = (fib(1) + fib(0)) + fib(1) = (1 + 0) +fib(1) = 1 + fib(1) = 1 + 1 = 2

40. Fibonacci Numbers, cont ComputeFibonacci

41. Fibonnaci Numbers, cont.

42. Towers of Hanoi Example 4.10 Solving the Towers of Hanoi Problem Solve the towers of Hanoi problem. TowersOfHanoi

43. Towers of Hanoi, cont.

44. Exercise 4.11 GCD gcd(2, 3) = 1 gcd(2, 10) = 2 gcd(25, 35) = 5 gcd(205, 301) = 5 gcd(m, n) Approach 1: Brute-force, start from min(n, m) down to 1, to check if a number is common divisor for both m and n, if so, it is the greatest common divisor. Approach 2: Euclid’s algorithm Approach 3: Recursive method

45. Approach 2: Euclid’s algorithm // Get absolute value of m and n; t1 = Math.abs(m); t2 = Math.abs(n); // r is the remainder of t1 divided by t2; r = t1 % t2; while (r != 0) { t1 = t2; t2 = r; r = t1 % t2; } // When r is 0, t2 is the greatest common divisor between t1 and t2 return t2;

46. Approach 3: Recursive Method gcd(m, n) = n if m % n = 0; gcd(m, n) = gcd(n, m % n); otherwise;

47. Chapter 3 Control Statements F Selection Statements –Using if and if...else –Nested if Statements –Using switch Statements –Conditional Operator F Repetition Statements –Looping: while, do-while, and for –Nested loops –Using break and continue

48. Selection Statements  if Statements  switch Statements F Conditional Operators

49. if Statements if (booleanExpression) { statement(s); } Example: if (i > 0 && i < 10) { System.out.println("i is an " + "integer between 0 and 10"); }

50. Caution Adding a semicolon at the end of an if clause is a common mistake. if (radius >= 0); { area = radius*radius*PI; System.out.println( "The area for the circle of radius " + radius + " is " + area); } This mistake is hard to find, because it is not a compilation error or a runtime error, it is a logic error. This error often occurs when you use the next-line block style. Wrong

51. The if...else Statement if (booleanExpression) { statement(s)-for-the-true-case; } else { statement(s)-for-the-false-case; }

52. if...else Example if (radius >= 0) { area = radius * radius * 3.14159; System.out.println("The area for the “ + “circle of radius " + radius + " is " + area); } else { System.out.println("Negative input"); }

53. Multiple Alternative if Statements if (score >= 90) grade = ‘A’; else if (score >= 80) grade = ‘B’; else if (score >= 70) grade = ‘C’; else if (score >= 60) grade = ‘D’; else grade = ‘F’; if (score >= 90) grade = ‘A’; else if (score >= 80) grade = ‘B’; else if (score >= 70) grade = ‘C’; else if (score >= 60) grade = ‘D’; else grade = ‘F’;

54. Note The else clause matches the most recent if clause in the same block. For example, the following statement int i = 1; int j = 2; int k = 3; if (i > j) if (i > k) System.out.println("A"); else System.out.println("B"); is equivalent to int i = 1; int j = 2; int k = 3; if (i > j) if (i > k) System.out.println("A"); else System.out.println("B");

55. Note, cont. Nothing is printed from the preceding statement. To force the else clause to match the first if clause, you must add a pair of braces: int i = 1; int j = 2; int k = 3; if (i > j) { if (i > k) System.out.println("A"); } else System.out.println("B"); This statement prints B.

56. Example 3.1 Computing Taxes The US federal personal income tax is calculated based on the filing status and taxable income. There are four filing status: single filers, married filing jointly, married filing separately, and head of household. The tax rates for 2002 are shown in Table 3.1.

57. Example 3.1 Computing Taxes Compute Tax

58. switch Statements switch (status) { case 0: compute taxes for single filers; break; case 1: compute taxes for married file jointly; break; case 2: compute taxes for married file separately; break; case 3: compute taxes for head of household; break; default: System.out.println("Errors: invalid status"); System.exit(0); }

59. switch Statement Flow Chart

60. switch Statement Rules The switch-expression must yield a value of char, byte, short, or int type and must always be enclosed in parentheses. The value1,..., and valueN must have the same data type as the value of the switch-expression. The resulting statements in the case statement are executed when the value in the case statement matches the value of the switch-expression. (The case statements are executed in sequential order.) The keyword break is optional, but it should be used at the end of each case in order to terminate the remainder of the switch statement. If the break statement is not present, the next case statement will be executed.

61. switch Statement Rules, cont. The default case, which is optional, can be used to perform actions when none of the specified cases is true. The order of the cases (including the default case) does not matter. However, it is a good programming style to follow the logical sequence of the cases and place the default case at the end.

62. Conditional Operator if (x > 0) y = 1 else y = -1; is equivalent to y = (x > 0) ? 1 : -1; Ternary operator Binary operator Unary operator

63. Conditional Operator if (num % 2 == 0) System.out.println(num + “is even”); else System.out.println(num + “is odd”); System.out.println( (num % 2 == 0)? num + “is even” : num + “is odd”);

64. Conditional Operator, cont. (booleanExp) ? exp1 : exp2

65. Repetitions  while Loops  do-while Loops  for Loops  break and continue

66. while Loop Flow Chart while (continuation-condition) { // loop-body; }

67. while Loop Flow Chart, cont. int i = 0; while (i < 100) { System.out.println( "Welcome to Java!"); i++; }

68. Example 3.2: Using while Loops TestWhile.java TestWhile

69. Caution Don’t use floating-point values for equality checking in a loop control. Since floating-point values are approximations, using them could result in imprecise counter values and inaccurate results. This example uses int value for data. If a floating-point type value is used for data, (data != 0) may be true even though data is 0. // data should be zero double data = Math.pow(Math.sqrt(2), 2) - 2; if (data == 0) System.out.println("data is zero"); else System.out.println("data is not zero");

70. do-while Loop do { // Loop body; } while (continuation-condition);

71. for Loops for (initial-action; loop-continuation-condition; action-after-each-iteration) { //loop body; } int i = 0; while (i < 100) { System.out.println("Welcome to Java!" + i); i++; } Example: int i; for (i = 0; i < 100; i++) { System.out.println("Welcome to Java!" + i); }

72. for Loop Flow Chart for (initial-action; loop-continuation-condition; action-after-each-iteration) { //loop body; }

73. for Loop Example int i; for (i = 0; i<100; i++) { System.out.println( "Welcome to Java"); }

74. for Loop Examples Examples for using the for loop: F Example 3.3: Using for Loops TestSum TestMulTable F Example 3.4: Using Nested for Loops

75. Which Loop to Use? The three forms of loop statements, while, do-while, and for, are expressively equivalent; that is, you can write a loop in any of these three forms. I recommend that you use the one that is most intuitive and comfortable for you. In general, a for loop may be used if the number of repetitions is known, as, for example, when you need to print a message 100 times. A while loop may be used if the number of repetitions is not known, as in the case of reading the numbers until the input is 0. A do-while loop can be used to replace a while loop if the loop body has to be executed before testing the continuation condition.

76. Caution Adding a semicolon at the end of the for clause before the loop body is a common mistake, as shown below: for (int i=0; i<10; i++); { System.out.println("i is " + i); } Logic Error

77. Caution, cont. Similarly, the following loop is also wrong: int i=0; while (i < 10); { System.out.println("i is " + i); i++; } In the case of the do loop, the following semicolon is needed to end the loop. int i=0; do { System.out.println("i is " + i); i++; } while (i<10); Logic Error Correct

78. The break Keyword

79. The continue Keyword

80. Using break and continue Examples for using the break and continue keywords: F Example 3.5: TestBreak.java F Example 3.6: TestContinue.java TestBreak TestContinue

81. Example 3.7 Finding the Sales Amount You have just started a sales job in a department store. Your pay consists of a base salary and a commission. The base salary is $5,000. The scheme shown below is used to determine the commission rate. Sales AmountCommission Rate $0.01–$5,0008 percent $5,000.01–$10,00010 percent $10,000.01 and above12 percent Your goal is to earn $30,000 in a year. Write a program that will find out the minimum amount of sales you have to generate in order to make $30,000. FindSalesAmountRun

82. Example 3.8 Displaying a Pyramid of Numbers In this example, you will use nested loops to print the following output: 1 212 32123 4321234 543212345 Your program prints five lines. Each line consists of three parts. The first part comprises the spaces before the numbers; the second part, the leading numbers, such as 3 2 1 on line 3; and the last part, the ending numbers, such as 2 3 on line 3. PrintPyramidRun

83. Example 3.9 Displaying Prime Numbers This example displays the first 50 prime numbers in five lines, each of which contains 10 numbers. An integer greater than 1 is prime if its only positive divisor is 1 or itself. For example, 2, 3, 5, and 7 are prime numbers, but 4, 6, 8, and 9 are not. The problem can be broken into the following tasks: For number = 2, 3, 4, 5, 6,..., test whether the number is prime. Determine whether a given number is prime. Count the prime numbers. Print each prime number, and print 10 numbers per line. PrimeNumberRun