1. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 1 Lecture 2&3 Primitive Data Types and Operations F Introduce Programming with an Example F Identifiers, Variables, and Constants F Primitive Data Types –byte, short, int, long, float, double, char, boolean F Expressions F Operators, Precedence, Associativity, Operand Evaluation Order: ++, --, *, /, %, +=, -=, *=, /=, %=, ^, &, |, +, -,  Getting Input from Input Dialog Boxes F Style and Documentation Guidelines F Syntax Errors, Runtime Errors, and Logic Errors

2. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 2 Introducing Programming with an Example  Example 2.1 Computing the Area of a Circle This program computes the area of the circle. ComputeAreaRun

3. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 3 Identifiers  An identifier is a sequence of characters that consist of letters, digits, underscores (_), and dollar signs ($).  An identifier must start with a letter, an underscore (_), or a dollar sign ($). It cannot start with a digit.  An identifier cannot be a reserved word.  An identifier cannot be true, false, or null.  An identifier can be of any length.

4. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 4 Variables F // Compute the first area radius = 1.0; area = radius*radius*3.14159; System.out.println("The area is “ + area + " for radius "+radius); F // Compute the second area radius = 2.0; area = radius*radius*3.14159; System.out.println("The area is “ + area + " for radius "+radius);

5. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 5 Declaring Variables F int x; // Declare x to be an // integer variable; F double radius; // Declare radius to // be a double variable; F char a; // Declare a to be a // character variable;

6. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 6 Assignment Statements  x = 1; // Assign 1 to x;  radius = 1.0; // Assign 1.0 to radius;  a = 'A'; // Assign 'A' to a;

7. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 7 Declaring and Initializing in One Step F int x = 1; F double d = 1.4; F float f = 1.4; Is this statement correct?

8. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 8 Constants F final datatype CONSTANTNAME = VALUE; F final double PI = 3.14159; F final int SIZE = 3;

9. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 9 Numerical Data Types  byte 8 bits  short 16 bits  int 32 bits  long 64 bits  float 32 bits  double 64 bits

10. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 10 Operators F +, -, *, /, and % F 5/2 yields an integer 2, due to integer division. F 5.0/2 yields a double value 2.5 F 5 % 2 yields 1 (the remainder of the division)

11. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 11 NOTE F Calculations involving floating-point numbers are approximated because these numbers are not stored with complete accuracy. For example, F System.out.println(1 - 0.1 - 0.1 - 0.1 - 0.1 - 0.1); F displays 0.5000000000000001, not 0.5, and F System.out.println(1.0 - 0.9); F displays 0.09999999999999998, not 0.1. F Integers are stored precisely. F Calculations with integers yield a precise integer result, but watch out for overflows.

12. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 12 Number Literals F A literal is a constant value that appears directly in the program. F Examples: –int i = 34; –long l = 1000000; –double d = 5.0;

13. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 13 Integer Literals  An integer literal can be assigned to an integer variable as long as it can fit into the variable.  A compilation error would occur if the literal were too large for the variable to hold.  For example, the statement byte b = 1000 would cause a compilation error.  An integer literal is assumed to be of the int type, whose value is between -2 31 (-2147483648) to 2 31 – 1 (2147483647).  To denote an integer literal of the long type, append it with the letter L (preferred) or l.

14. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 14 Floating-Point Literals  Floating-point literals are written with a decimal point.  By default, a floating-point literal is treated as a double type value.  For example, 5.0 is considered a double value, not a float value.  Make a number a float by appending the letter f or F, and make a number a double by appending the letter d or D.  For example, 100.2f or 100.2F is a float number, and 100.2d or 100.2D is a double number.

15. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 15 Scientific Notation  Floating-point literals can also be specified in scientific notation.  1.23456e+2 is same as 1.23456e2, is equivalent to 123.456, and 1.23456e-2 is equivalent to 0.0123456.  E (or e) represents an exponent.

16. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 16 Arithmetic Expressions is translated to (3+4*x)/5 – 10*(y-5)*(a+b+c)/x + 9*(4/x + (9+x)/y)

17. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 17 Shortcut Assignment Operators OperatorExampleEquivalent +=i+=8i = i+8 -=f-=8.0f = f-8.0 *=i*=8i = i*8 /=i/=8i = i/8 %=i%=8i = i%8

18. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 18 Increment and Decrement Operators

19. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 19 Increment and Decrement Operators, cont.

20. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 20 Increment and Decrement Operators, cont.  Using increment and decrement operators makes expressions short, but it may also make them complex and difficult to read.  Avoid using these operators in expressions that modify multiple variables, or the same variable for multiple times such as this: int k = ++i + i.

21. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 21 Assignment Expressions and Assignment Statements  Prior to Java 2, all expressions can be used as statements. Since Java 2, only the following types of expressions can be statements: –variable op= expression; // Where op is +, -, *, /, or % –++variable; –variable++; –--variable; –variable--;

22. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 22 Numeric Type Conversion  Consider the following statements:  byte i = 100;  long k = i*3+4;  double d = i*3.1+k/2;  int x = k; //(Wrong)  long k = x; //(fine,implicit casting)

23. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 23 Type Casting  (double)  (float)  (long)  (int)  (short)  (byte )

24. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 24 Type Casting, cont. F Implicit casting –double d = 3; (type widening) F Explicit casting –int i = (int)3.0; (type narrowing) F What is wrong?int x = 5/2.0;

25. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 25 Character Data Type F char letter = 'A'; (ASCII) F char numChar = '4'; (ASCII) F char letter = '\u0041'; (Unicode) F char numChar = '\u0034';(Unicode) F Special characters –char tab = ‘\t’;

26. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 26 Unicode Format Description Escape Sequence Unicode Backspace \b\u0008 Tab \t\u0009 Linefeed \n\u000a Carriage return \r\u000d

27. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 27 Casting between char and Numeric Types  int i = ' a ' ; // Same as int i = (int) ' a ' ;  char c = 97; // Same as char c = (char)97;

28. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 28 The boolean Type and Operators  boolean lightsOn = true;  boolean lightsOn = false;  boolean b = (1 > 2);  && (and) : (1 < x) && (x < 100)  || (or) : (lightsOn) || (isDayTime)  ! (not) : !(isStopped)

29. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 29 Comparison Operators Operator Name < less than <= less than or equal to > greater than >= greater than or equal to == equal to != not equal to

30. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 30 Boolean Operators Operator Name ! not && and || or ^ exclusive or

31. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 31 Truth Table for Operator ! Operand!Operand true false false true

32. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 32 Truth Table for Operator && Operand1Operand2Operand1 && Operand2 falsefalsefalse falsetruefalse truefalsefalse truetruetrue

33. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 33 Truth Table for Operator || Operand1Operand2Operand1 || Operand2 falsefalsefalse falsetruetrue truefalsetrue truetruetrue

34. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 34 Truth Table for Operator ^ Operand1Operand2Operand1 ^ Operand2 falsefalsefalse falsetruetrue truefalsetrue truetruefalse

35. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 35 The & and | Operators  &&: conditional AND operator  &: unconditional AND operator  ||: conditional OR operator  |: unconditional OR operator  Examples :  exp1 && exp2, such as (1 < x) && (x < 100)  exp1 || exp2, such as (1 < x) & (x < 100)

36. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 36 The & and | Operators F If x is 1, what is x after this expression? –(x > 1) & (x++ < 10) F If x is 1, what is x after this expression? –(1 > x) && ( 1 > x++) F How about (1 == x) | (10 > x++)? –(1 == x) || (10 > x++)?

37. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 37 Operator Precedence  How to evaluate 3 + 4 * 4 > 5 * (4 + 3) - ++i

38. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 38 Operator Precedence F var++, var--  +, - (Unary plus and minus), ++var, --var F (type) Casting F ! (Not)  *, /, % (Multiplication, division, and modulus)  +, - (Binary addition and subtraction) , >= (Comparison)  ==, !=; (Equality) F & (Unconditional AND) F ^ (Exclusive OR) F | (Unconditional OR) F && (Conditional AND) Short-circuit AND F || (Conditional OR) Short-circuit OR  =, +=, -=, *=, /=, %= (Assignment operator)

39. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 39 Operator Associativity  When two operators with the same precedence are evaluated, the associativity of the operators determines the order of evaluation.  All binary operators except assignment operators are left-associative.  a – b + c – d is equivalent to ((a – b) + c) – d  Assignment operators are right-associative. Therefore, the expression  a = b += c = 5 is equivalent to a = (b += (c = 5))

40. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 40 Operand Evaluation Order  Operands are evaluated from left to right in Java.  The left-hand operand of a binary operator is evaluated before any part of the right-hand operand is evaluated.

41. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 41 Operand Evaluation Order, cont.  If no operands have side effects that change the value of a variable, the order of operand evaluation is irrelevant.  Beware when operands do have a side effect. For example, x becomes 1 in the following code.  int a = 0; int x = a + (++a);  But x becomes 2 in the following code.  int a = 0; int x = ++a + a;

42. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 42 Getting Input from Input Dialog Boxes  String string = JOptionPane.showInputDialog( null, “Prompt Message”, “Dialog Title”, JOptionPane.QUESTION_MESSAGE)); where the second parameter is a string for the prompting message and the fourth parameter is a string for the title of the input dialog box.

43. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 43 Getting Input from Input Dialog Boxes (Cont’d)  JOptionPane.showInputDialog(parentComponent, objectExpression, boxTitleString, messageType); ParameterDescription parentComponentAn object that represents the parent of the dialog box. Default is null causing the dialog box to appear in the middle of the screen. objectExpressionThis expression is usually the string that appears in the dialog box. boxTitleStringThis is the title of the dialog box. messageTypeAn int value controlling the type of icon that will appear in the dialog box. You can use the JOptionPane options. messageTypeDescription JOptionPane.ERROR_MESSAGEThe error icon is displayed in the dialog box. JOptionPane.INFORMATION_MESSAGEThe information icon is displayed in the dialog box. JOptionPane.PLAIN_MESSAGENo icon appears in the dialog box. JOptionPane.QUESTION_MESSAGEThe question mark icon is displayed in the dialog box. JOptionPane.WARNING_MESSAGEThe exclamation icon is displayed in the dialog box.

44. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 44 Convertting Strings to Integers  The input returned from the input dialog box is a string. If you enter a numeric value such as 123, it returns “123”.  To obtain the input as a number, you have to convert a string into a number.  To convert a string into an int value, you can use the static parseInt method in the Integer class as follows:  int intValue = Integer.parseInt(intString); where intString is a numeric string such as “123”.

45. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 45 Convertting Strings to Doubles  To convert a string into a double value, you can use the static parseDouble method in the Double class as follows:  double doubleValue =Double.parseDouble(doubleString); where doubleString is a numeric string such as “123.45”.

46. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 46 Example 2.2 Entering Input from Dialog Boxes InputDialogDemoRun  This program first prompts the user to enter a year as an int value and checks if it is a leap year, it then prompts you to enter a double value and checks if it is positive.  A year is a leap year if it is divisible by 4 but not by 100, or it is divisible by 400.

47. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 47 // InputDialogDemo.java: Entering input from input dialog boxes import javax.swing.JOptionPane; public class InputDialogDemo { public static void main(String args[]) { // Prompt the user to enter a year String yearString = JOptionPane.showInputDialog(null, "Enter a year:", "Example 2.2 Input (int)", JOptionPane.QUESTION_MESSAGE); // Convert the string into an int value int year = Integer.parseInt(yearString); // Check if the year is a leap year boolean isLeapYear = ((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0); // Display the result in a message dialog box JOptionPane.showMessageDialog(null, year + " is a leap year? " + isLeapYear, "Example 2.2 Output (int)", JOptionPane.INFORMATION_MESSAGE); // Prompt the user to enter a double value String doubleString = JOptionPane.showInputDialog(null, "Enter a double value:", "Example 2.2 Input (double)", JOptionPane.QUESTION_MESSAGE); // Convert the string into a double value double doubleValue = Double.parseDouble(doubleString); // Check if the number is positive JOptionPane.showMessageDialog(null, doubleValue + " is positive? " + (doubleValue > 0), Example 2.2 Output (double)", JOptionPane.INFORMATION_MESSAGE); System.exit(0); }

48. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 48 Example 2.3 Computing Mortgages ComputeMortgageRun  This program lets the user enter the interest rate, number of years, and loan amount and computes monthly payment and total payment.

49. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 49 // ComputeMortgage.java: Compute mortgage payments import javax.swing.JOptionPane; public class ComputeMortgage { /** Main method */ public static void main(String[] args) { double annualInterestRate; int numOfYears; double loanAmount; // Enter yearly interest rate String annualInterestRateString = JOptionPane.showInputDialog(null, "Enter yearly interest rate, for example 8.25:","Example 2.3 Input", JOptionPane.QUESTION_MESSAGE); // Convert string to double annualInterestRate = Double.parseDouble(annualInterestRateString); // Obtain monthly interest rate double monthlyInterestRate = annualInterestRate/1200; // Enter number of years String numOfYearsString = JOptionPane.showInputDialog(null, "Enter number of years as an integer,\nfor eg 5:", "EG 2.3 Input", JOptionPane.QUESTION_MESSAGE); // Convert string to int numOfYears = Integer.parseInt(numOfYearsString); // Enter loan amount String loanString = JOptionPane.showInputDialog(null, "Enter loan amount, for example 120000.95:", "Example 2.3 Input", JOptionPane.QUESTION_MESSAGE); // Convert string to double loanAmount = Double.parseDouble(loanString); // Calculate payment double monthlyPayment=loanAmount*monthlyInterestRate/1 - 1/Math.pow(1+monthlyInterestRate, numOfYears*12)); double totalPayment = monthlyPayment * numOfYears * 12; // Format to keep two digits after the decimal point monthlyPayment = (int)(monthlyPayment * 100) / 100.0; totalPayment = (int)(totalPayment * 100) / 100.0; // Display results String output = "The monthly payment is " + monthlyPayment + "\nThe total payment is " + totalPayment; JOptionPane.showMessageDialog(null, output, "EG 2.3 Output", JOptionPane.INFORMATION_MESSAGE); System.exit(0); }

50. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 50 Example 2.4 Computing Changes  This program lets the user enter the amount in decimal representing dollars and cents and output a report listing the monetary equivalent in 10 dollar coins, 5 dollar coins, 2 dollar coins, 1 dollar coins, 50 cent coins, 20 cent coins and 10 cent coins. Your program should report maximum number of 10 dollar coins, then the maximum number of 5 dollar coins, and so on, in this order. ComputeChangeRun

51. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 51 // ComputeChange.java: Break down an amount into smaller units import javax.swing.JOptionPane; public class ComputeChange { public static void main(String[] args) { double amount; // Amount entered from the keyboard // Receive the amount entered from the keyboard and convert to double String amountString = JOptionPane.showInputDialog(null,"Enter an amount in double, for eg 11.50", "Example 2.4 Input", JOptionPane.QUESTION_MESSAGE); amount = Double.parseDouble(amountString); int remainingAmount = (int)(amount * 100); // Find the number of 10 dollar coins int numOf10Dollars = remainingAmount / 1000; remainingAmount = remainingAmount % 1000; // Find the number of 5 dollar coins int numOf5Dollars = remainingAmount / 500; remainingAmount = remainingAmount % 500; // Find the number of 2 dollar coins int numOf2Dollars = remainingAmount / 200; remainingAmount = remainingAmount % 200; // Find the number of one dollars int numOf1Dollars = remainingAmount / 100; remainingAmount = remainingAmount % 100; // Find the number of 50 cent coins the remaining amount int numOf50Cents = remainingAmount / 50; remainingAmount = remainingAmount % 50; // Find the number of 20 cent coins in the remaining amount int numOf20Cents = remainingAmount / 20; remainingAmount = remainingAmount % 20; // Find the number of 10 cents coins in the remaining amount int numOf10Cents = remainingAmount / 10; // Display results, ignoring remaining cents String output = "Your amount " + amount + " consists of \n" + numOf10Dollars + " 10 dollars\n" + numOf5Dollars + " 5-dollars\n" + numOf2Dollars + " 2-dollars\n" + numOf1Dollars + " 1-dollars\n" + numOf50Cents + " 50-cents\n" + numOf20Cents + " 20-cents\n" + numOf10Cents + " 10-cents\n" +"Remaining cents ignored"; JOptionPane.showMessageDialog(null, output, "EG 2.4 Output", JOptionPane.INFORMATION_MESSAGE); System.exit(0); }

52. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 52 Programming Style and Documentation F Appropriate Comments F Naming Conventions F Proper Indentation and Spacing Lines F Block Styles

53. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 53 Appropriate Comments  Include a summary at the beginning of the program to explain what the program does, its key features, its supporting data structures, and any unique techniques it uses.  Include your name, class section, instruction, date, and a brief description at the beginning of the program.

54. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 54 Naming Conventions  Choose meaningful and descriptive names.  Variables and method names:  Use lowercase.  If the name consists of several words, concatenate all in one, use lowercase for the first word, and capitalize the first letter of each subsequent word in the name.  Examples :  Radius;  area, and  the method computeArea.

55. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 55 Naming Conventions, cont.  Class names:  Capitalize the first letter of each word in the name.  Example : ComputeArea.  Constants:  Capitalize all letters in constants.  Example : the constant PI.

56. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 56 Proper Indentation and Spacing  Indentation  Indent two spaces.  Spacing  Use blank line to separate segments of the code.

57. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 57 Block Styles  Use end-of-line style for braces.

58. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 58 Programming Errors  Syntax Errors  Detected by the compiler  Runtime Errors  Causes the program to abort  Logic Errors  Produces incorrect result

59. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 59 Compilation Errors public class ShowSyntaxErrors { public static void main(String[] args) { i = 30; System.out.println(i+4); }

60. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 60 Runtime Errors public class ShowRuntimeErrors { public static void main(String[] args) { int i = 1 / 0; }

61. S.W.Ma/CIM/LWL41211/2 Prog. IIA Page 61 Logic Errors public class ShowLogicErrors { // Determine if a number is between 1 and 100 inclusively public static void main(String[] args) { // Prompt the user to enter a number String input = JOptionPane.showInputDialog(null, "Please enter an integer:", "ShowLogicErrors", JOptionPane.QUESTION_MESSAGE); int number = Integer.parseInt(input); // Display the result System.out.println("The number is between 1 and 100, " + "inclusively? " + ((1 < number) && (number < 100))); System.exit(0); }