1. Chapter 2: Java Fundamentals cont’d

2. Outline 2.1 The Parts of a Java Program
2.2 The print and println Methods, and the Java Standard Class Library
2.3 Variables and Literals
2.4 Primitive Data Types
2.5 Arithmetic Operators
2.6 Combined Assignment Operators
2.7 Conversion Between Primitive Types
2.8 Creating Named Constants with final
2.9 The String Class
2.10 Scope
2.11 Comments
2.12 Programming Style
2.13 Reading Keyboard Input
2.14 Dialog Boxes
2.15 Common Errors to Avoid

3. The % operator Returns the remainder of the division Examples;

4. Exercise Write the following in a Java file: double amount = 137/5;
System.out.println(“Amount is : “ + amount );
amount = 137.0/5;

5. Integer Division
Dividing an integer by an integer gives an integer  the remainder is ignored
Examples:
5/4 is 1
17/3 is 5

6. Operator Precedence What is the result of: Polynomial = 1+2*3+ 6/2 -2;
Is it ?
(1+2)*3 + 6/(2-2)
1+(2*3) +(6/2)-2
(1+2)*3 + (6/2)-2

7. Precedence Rules Always evaluate * , / and % before + and –
Always negate before any calculations
*, / and % have same precedence
+ and – have same precedence
If equal precedence then evaluate from left to right except for negations where we evaluate from right to left

8. Precedence examples Polynomial = 1+2*3+ 6/2 – 2;
Polynomial has the value of =8
Polynomial = –1 + 5 – 2; // 2
Polynomial = –(–3) + –(–5); //8

9. Grouping with parentheses
You can use parentheses to force the evaluation of a formula
Examples:
x * ( y + z*z ) instead of x*y + z*z
x * ( y * ( z ) + 85 ) – 65
Average = (a +b +c ) /3;

10. The Math class
value = Math.pow( x,y); // now value holds x to the power of y
value = Math.sqrt( x); //now value holds the square root of x

11. Combined Assignment Operators+=
x += 1;
x = x + 1; –=
x –= 1;
x = x – 1; *=
x *= 1;
x = x * 1; /=
x /= 1;
x = x / 1; %=
x %= 1;
x = x % 1;

12. Operator Precedence What is the result of: Polynomial = 1+2*3+ 6/2 -2;
Is it ?
(1+2)*3 + 6/(2-2)
1+(2*3) +(6/2)-2
(1+2)*3 + (6/2)-2

13. Precedence Rules Always evaluate * , / and % before + and –
Always negate before any calculations
*, / and % have same precedence
+ and – have same precedence
If equal precedence then evaluate from left to right except for negations where we evaluate from right to left

14. Precedence examples Polynomial = 1+2*3+ 6/2 – 2;
Polynomial has the value of =8
Polynomial = –1 + 5 – 2; // 2
Polynomial = –(–3) + –(–5); //8

15. Grouping with parentheses
You can use parentheses to force the evaluation of a formula
Examples:
x * ( y + z*z ) instead of x*y + z*z
x * ( y * ( z ) + 85 ) – 65
Average = (a +b +c ) /3;

16. The Math class
value = Math.pow( x,y); // now value holds x to the power of y
value = Math.sqrt( x); //now value holds the square root of x

17. Combined Assignment Operators+=
x += 1;
x = x + 1; –=
x –= 1;
x = x – 1; *=
x *= 1;
x = x * 1; /=
x /= 1;
x = x / 1; %=
x %= 1;
x = x % 1;

18. 2.7 Conversion between Primitive Data Types
Before a value is stored in a variable, Java checks the Data Type of the value and the variable
If the data types are compatible then Java performs the conversion automatically  No Error
If the data types are not compatible then Java issues an error.

19. 2.7 Conversion between Primitive Data Types
A widening conversion is the conversion of a small value to a larger one
A narrowing conversion is the conversion of a large value to a smaller one
double largest
float
long
int
short
byte smallest

20. Widening conversion Example 1: Example 2: double x; int y = 10; x = y;
int x;
short y =2;
x= y;

21. Narrowing Conversion
We have to perform casting i.e. the name of the smaller data type is put in parentheses in front of the value
Example:
int number;
double pi = 3.14;
number = (int) pi;

22. Cast operator Used to convert from one primitive data type to another
Must be used for narrowing conversions

23. Example: int pies = 10, people = 4; double piesPerPerson;
piesPerPerson = pies /people;
piesPerPerson =(double) pies/people;
piesPerPerson =pies/(double) people;
piesPerPerson=(double)(pies/people);
(double)(10/4) = (double)(2) = 2.0
because it is an integer division
10/4 = 2 because it is an integer division
10.0/4 = 2.5 because one of the numbers
is a double
10/4.0 = 2.5 because people is double

24. Mixed Integer Operations
The result of an arithmetic operation that involves only byte, short, or int variables is always an int even if both variables are of data type short or byte
Example:
short x =5, y =7;
short z = x+y; // this statement gives an error
short z = (short) ( x+y ); //correct

25. Mixed Integer Operations
If one of the operator’s operands is a double then the result of the operation is a double
If one of the operator’s operands is a float then the result of the operation is a float
If one of the operator’s operands is a long then the result of the operation is a long

26. Creating named constants with final
A named constant is a variable whose value is read-only and cannot be changed
To create a named constant add the word final to declaration
An initialization value is required when declaring a constant
Example:
final double INTEREST_RATE = 0.069;

27. More about named constants
When naming a constant, the variable name should be written in all uppercase characters.
Math.PI is a constant that holds the value of pi ( i.e …)
Math.PI is already declared and initialized so it ready to use. Example:
double area = Math.PI * radius * radius ;

28. The String class A String literal is any text enclosed in quotations
A String is the DataType of a variable that can store String literals
Example of a String variable:
String name = “CS 0007”;
System.out.println( name );

29. The String class
To determine how many letters are stored in a String variable (name) use name.length();
Example:
String mycourse = “CS 0007”;
int number = mycourse.length();

30. String methods charAt(index)
index is an integer and specifies the character position in the String
This method returns the character at the specified position
Example:
char letter;
String myText = “This is my Text”;
letter = myText.charAt(8);

31. T h i s m y e x t String methods myText.length returns 15
because there are 15 characters T h i s m y e x t 1 2 3 4 5 6 7 8 9 10 11 12 13 14
myText.charAt(8) returns m
because m is the letter at position 8

32. String methods toLowerCase()
This method returns a new String that has all of the characters of the original String but in lowercase
Example:
String bigName = “I am BIG!!”;
String smallName =
bigName.toLowerCase();
// now smallName holds “i am big!!”

33. String methods toUpperCase()
Same as toLowerCase() but it converts all the characters to uppercase
Example:
String smallName = “I am Big!!”;
String bigName =
smallName.toUpperCase();
// now bigName holds “I AM BIG!!”

34. Example: String message = "Java is Great Fun!";
String upper = message.toUpperCase();
String lower = message.toLowerCase();
char letter = message.charAt(2);
int stringSize = message.length();
System.out.println(message);
System.out.println(upper);
System.out.println(lower);
System.out.println(letter);
System.out.println(stringSize);

35. Scope
The variable scope is the part of the program that has access to it
public class Scope {
public static void main(String[] args)
System.out.println(value); // ERROR!
int value = 100; }

36. Scope public class Scope { public static void main(String[] args){
int number = 100;
System.out.println(number);
int number = 200; //ERROR }

37. Comments Java provides three methods for commenting code.//
Single line comment. Anything after the // on the line will be ignored by the compiler.
/* … */
Block comment. Everything beginning with /* and ending with the first */ will be ignored by the compiler. This comment type cannot be nested.
/** … */
Javadoc comment. This is a special version of the previous block comment that allows comments to be documented by the javadoc utility program. Everything beginning with the /** and ending with the first */ will be ignored by the compiler. This comment type cannot be nested.

38. Programming Style
Although Java has a strict syntax, whitespace characters are ignored by the compiler.
The Java whitespace characters are:
space
tab
newline
carriage return
form feed

39. Programming Style
public class Compact {public static void main(String[] args){int shares=220; double averagePrice=14.67; System.out.println("There were "+shares+" shares sold at $"+averagePrice+ " per share.");}}
Compiles !!!

40. Indentation Programs should use proper indentation.
Each block of code should be indented a few spaces from its surrounding block.
Two to four spaces are sufficient

41. Programming Style
/**
This example is much more readable than Compact.java. */
public class Readable {
public static void main(String[] args)
int shares = 220;
double averagePrice = 14.67;
System.out.println("There were " + shares +
" shares sold at $" +
averagePrice + " per share."); }

42. Dialog Boxes
A dialog box is a small graphical window that displays a message to the user or requests input.
A variety of dialog boxes can be displayed using the JOptionPane class.
Two of the dialog boxes are:
Message Dialog - a dialog box that displays a message.
Input Dialog - a dialog box that prompts the user for input.

43. Using the import Statement
The JOptionPane class is not automatically available to your Java programs.
The following statement must be before the program’s class header:
import javax.swing.JOptionPane;
This statement tells the compiler where to find the JOptionPane class. 

44. Dialog Boxes
The JOptionPane class provides static methods to display each type of dialog box.

45. Message Dialogs
JOptionPane.showMessageDialog method is used to display a message dialog.
JOptionPane.showMessageDialog(null, "Hello World");
The second argument is the message that is to be displayed.

46. Input Dialogs
An input dialog is a quick and simple way to ask the user to enter data.
The dialog displays a text field, an Ok button and a Cancel button.
If Ok is pressed, the dialog returns the user’s input.
If Cancel is pressed, the dialog returns null.

47. Input Dialogs
String name;
name = JOptionPane.showInputDialog(
"Enter your name.");
The argument passed to the method is the message to display.
If the user clicks on the OK button, name references the string entered by the user.
If the user clicks on the Cancel button, name references null.

48. NamesDialog.java import javax.swing.JOptionPane;
public class NamesDialog {
public static void main(String[] args)
String firstName; // The user's first name
String middleName; // The user's middle name
String lastName; // The user's last name
// Get the user's first name
firstName =
JOptionPane.showInputDialog("What is " +
"your first name? ");

49. NamesDialog.java // Get the user's middle name. middleName =
JOptionPane.showInputDialog(
"What is " + "your middle name? ");
// Get the user's last name.
lastName =
JOptionPane.showInputDialog("What is " + "your last name? ");

50. Example // Display a greeting
JOptionPane.showMessageDialog(null, "Hello " + firstName + " " +middleName + " " + lastName);
System.exit(0); }

51. The System.exit() Method
A program that uses JOptionPane does not automatically stop executing when the end of the main method is reached.
Java generates a thread, which is a process running in the computer, when a JOptionPane is created.
If the System.exit method is not called, this thread continues to execute.

52. The System.exit() Method
The System.exit method requires an integer argument.
System.exit(0);
This argument is an exit code that is passed back to the operating system.
This code is usually ignored, however, it can be used outside the program:
to indicate whether the program ended successfully or as the result of a failure.
The value 0 traditionally indicates that the program ended successfully.

53. Converting a String to a Number
The JOptionPane’s showInputDialog method always returns the user's input as a String
String containing a number, such as “127.89, can be converted to a numeric data type.

54. The Parse Methods Parse methods convert strings to numeric data types
They are:
Byte.parseByte
Integer.parseInt
Short.parseShort
Long.parseLong
Float.parseFloat
Double.parseDouble

55. The Parse Methods- Examples
byte bVar = Byte.parseByte("1");
int iVar = Integer.parseInt("2599");
short sVar = Short.parseShort("10");
long lVar = Long.parseLong("15908");
float fVar = Float.parseFloat("12.3");
double dVar = Double.parseDouble("7945.6");

56. PayrollDialog.java import javax.swing.JOptionPane;
public class PayrollDialog {
public static void main(String[] args)
String inputString; // For reading input
String name; // The user's name
int hours; // The number of hours worked
double payRate; // The user's hourly pay rate
double grossPay; // The user's gross pay

57. PayrollDialog.java // Get the user's name.
name = JOptionPane.showInputDialog("What is " "your name? ");
// Get the hours worked.
inputString =
JOptionPane.showInputDialog(
"How many hours” +
“ did you work this week? ");
// Convert the input to an int.
hours = Integer.parseInt(inputString);

58. PayrollDialog.java // Get the hourly pay rate. inputString =
JOptionPane.showInputDialog("What is” + " your hourly pay rate? ");
// Convert the input to a double.
payRate = Double.parseDouble(inputString);
// Calculate the gross pay.
grossPay = hours * payRate;

59. PayrollDialog.java // Display the results.
JOptionPane.showMessageDialog(null, "Hello " + name + ". Your gross pay is $" + grossPay);
// End the program.
System.exit(0); }