1. Chapter 2 Java Fundamentals

2. Contents The Parts of a Java Program
The print and println Methods, and the Java API
Variables and Literals
Primitive Data Types
Arithmetic Operators
Combined Assignment Operators
Conversion between Primitive Types
Creating Named Constraints with final

3. Contents The String Class Scope Comments Programming Style
Reading Keyboard Input
Dialog Box

4. 1. The Parts of a Java Program
Problem
Write a Java program to display a message (Programming is great fun!) on the screen.

5. 1. The Parts of a Java Program (Cont’d)
Run eclipse
Create a new Java project
Enter the project name: MyFirstProject
Create a new Java class:
Enter the class name: Simple
This will create a source code file Simple.java
Enter the code

6. 1. The Parts of a Java Program (Cont’d)

7. 1. The Parts of a Java Program (Cont’d)
Run the program

8. 1. The Parts of a Java Program (Cont’d)
Line 1:
//This is a simple Java program
// :
marks the beginning of a comment.
The compiler ignores everything from the double-slash to the end of the line. You can type anything you want.
Comments help explain what’s going on.

9. 1. The Parts of a Java Program (Cont’d)
Line 2:
A blank line
Programmers often insert blank lines in programs to make them easier to read.
Line 3:
public class Simple
This is a class header, and it marks the beginning of a class definition.

10. 1. The Parts of a Java Program (Cont’d)
A Java program must have at least one class definition.
public:
public is a Java keyword
must be written in all lowercase letters
public is an access specifier, and it controls where the class may be accessed from. The public specifier means access to the class is unrestricted (the class is “open to the public”).

11. 1. The Parts of a Java Program (Cont’d)
class:
a Java keyword, must be written in lowercase letter.
indicates the beginning of a class definition.
Simple:
Simple is the class name which is made up by the programmer. Programmer-defined names may be written in lowercase letters, uppercase letters, or a mixture of both.

12. 1. The Parts of a Java Program (Cont’d)
public class Simple
tell the compiler that a public accessible class named Simple is being defined.
We can create more than one class in a file, but we may only have one public class per Java file.
When a Java file has a public class, the name of the public class must be the same as the name of the file (without the .java extension).
Java is a case-sensitive language.
Public ≠ public ≠ puBlic ≠ pUblic …

13. 1. The Parts of a Java Program (Cont’d)
Line 4: {
is a left brace, or an opening brace, and is associated with the beginning of the class definition.
All programming statements that are parts of class are enclosed in a set of braces. In line 9, we will have the closing brace.
Everything between the two braces is the body of the class named Simple.

14. 1. The Parts of a Java Program (Cont’d)

15. 1. The Parts of a Java Program (Cont’d)
Name of the method
Line 5:
public static void main(String[] args)
a method header, the beginning of a method.
main is a name of the method. Every Java program must have a method named main. The main method is the starting point of an application.

16. 1. The Parts of a Java Program (Cont’d)
Line 6: {
This opening brace belongs to the main method. Every opening brace must have a accompanying closing brace.
We will have a closing brace in line 8 that corresponds with this opening brace.
Everything between these braces is the body of the main method.

17. 1. The Parts of a Java Program (Cont’d)
Line 7:
System.out.println("Programming is great fun!");
This line is a statement. It displays a message on the screen. The message, “Programming is great fun!”, is printed without the quotation marks.
The group of characters inside the quotation marks is called a string literal.
There is a semicolon at the end of this line. Semicolon marks end of a statement in Java.

18. 1. The Parts of a Java Program (Cont’d)
Not every line of code ends with a semicolon:
Comments do not have to end with a semicolon
Class headers and method headers do not end with a semicolon.
The brace characters, { and }, are not statements, so we do not place a semicolon after them.
Lines 8 and 9 contain the closing braces for main method and the class definition.

19. 1. The Parts of a Java Program (Cont’d)
Java is a case-sensitive language.
All Java program must be stored in a file with a name that ends with .java
Comments are ignored by the compiler.
A .java file may contain many classes, but may only have one public class.
If a .java file has a public class, the class must have the same name as the file.

20. 1. The Parts of a Java Program (Cont’d)
Every Java application program must have a method named main.
For every brace, or opening brace, there must be a corresponding right brace, or closing brace.
Statements are terminated with semicolons. This does not include comments, class headers, method headers, or braces.

21. 2. The print and println Methods, and Java API
are used to display text output.
are parts of the Java API (Application Programmer Interface).
API is a collection of prewritten classes and methods for performing specific operations.
The console
Standard output: the monitor
Standard input: the keyboard

22. 2. The print and println Methods, and Java API
System.out.println("Programming is great fun!");
Hierarchical Relationship among the System class, the out object, and the print and println methods

23. 2. The print and println Methods, and Java API
The System class is part of the java API. It has member objects and methods for performing system-level operations, such as sending output to the console.
The out object is a member of the System class. It provides methods for sending output to the screen.
The print and println methods are members of the out object. They actually perform the work of writing characters on the screen.
We use the period to separate System, out and print or println. The period is pronounced “dot”.

24. 2. The print and println Methods, and Java API
The value that is to be displayed on the screen is places inside the parentheses. This value is known as an argument.
System.out.println(“King Arthur”);
The println method is that after it displays its message, it advances the cursor to the beginning of the next line.

25. 2. The print and println Methods, and Java API

26. The print Method The print method part of the System.out object.
serves a purpose to display output on the screen.
does not advance the cursor to the next line after its message is displayed.

27. The print Method

28. The print Method

29. The print Method There are two ways to fix the Unruly program:
use println method ?
use escape sequences to separate the output into different lines
An escape sequence starts with the blackslash character (\), and is followed by one or more control characters.
The escape sequence that causes the output cursor to go to the next line is \n
\n is called the newline escape sequence.

30. The print Method

31. The print Method

32. Common Escape Sequences
See table 2-2
\n New line
\t Horizontal Tab
\b backspace
\r Return
\\ Backslash
\’ Single quote
\” Double quote

33. 3. Variables and Literals
A variable is a named storage location in the computer’s memory.
A literal is a value that is written into the code of a program.

34. 3. Variables and Literals (Cont’d)

35. 3. Variables and Literals (Cont’d)
Line 7:
int value;
Variable declaration
Variables must be declared before they can be used.
A variable declaration tells the compiler
the variable’ name
the type of data the variable will hold
variable’s name
data type

36. 3. Variables and Literals (Cont’d)
Line 9:
value=5;
Assignment statement
The equal sign = is an operator that stores the value on its right (5) into the variable named on its left (value).
After this line executes, the value variable will contain the value 5.

37. 3. Variables and Literals (Cont’d)

38. 3. Variables and Literals (Cont’d)
Line 11:
System.out.println(value);
The method println will display the variable’s contents on the console.
There are no quotation marks around variable value
Compare with System.out.println(“value”);

39. Display Multiple Items with the + Operator
The + operator is used with strings:
String concatenation operator
System.out.println(“This is ” + “one string.”);
This is one string.
The + operator can be used to concatenate the contents of a variable to a string
number = 5;
System.out.println(“The value is ” + number);
The value is 5

40. Display Multiple Items with the + Operator (Cont’d)
A string literal cannot begin on one line and end on another
System.out.println(“Enter a value that is greater than zero and less than 10.”);
Breaking the argument up into smaller string literals, and use the + operator
System.out.println(“Enter a value that” + “ is greater than zero and less “ + “than 10.”);
Error

41. Display Multiple Items with the + Operator (Cont’d)

42. Identifiers Identifier A programmer-defined name.
Do not use any of the Java keywords for identifiers.
Represents some element of a program.
Variable names, class names, name of methods, …

43. Identifiers (Cont’d)
Should choose names that give an indication of what they are used for, what the purpose is
For example
Number of ordered items
int x; not good
int itemsOrdered;

44. Identifiers (Cont’d) There are some rules with all identifiers:
The first character must be one of the letters a-z, A-Z, _, $
After the first character, we can use letters a-z, A-Z, digits 0-9, _, $
Uppercase and lowercase characters are distinct.
Identifiers cannot include spaces

45. Identifiers (Cont’d) Variable Name Legal or Illegal ? dayOfWeek Legal
3dGraph
Illegal
june1997
mixture#3
week day

46. Identifiers (Cont’d) Variable Names
It is standard practice to begin variable names with a lowercase letter
Capitalize the first the first letter of each subsequent word.
int itemOdered;

47. Identifiers (Cont’d) Class Names
It is standard practice to begin variable names with a uppercase letter
Capitalize the first letter of each subsequent word.
public class PayRoll

48. 4. Primitive Data Types
Each variable has a data type, which is the type of data that the variable can hold.
Selecting the proper type for variables is important
amount of memory
the way the variable formats and stores data

49. 4. Primitive Data Types (Cont’d)
Primitive data types for numeric data
Data Type
Size
Range
byte
1 byte
Integers in the range of -128 to +127
short
2 bytes
Integers in the range of -32,768 to +32,767
int
4 bytes
Integers in the range of -2,147,483,648 to +2,147,483,647
long
8 bytes
Integers in the range of -9,223,372,036,854,775,808 to +9,223,372,036,854,775,807
float
Floating-point numbers in the range of ±3.4×10-38 to ±3.4×1038 , with 7 digits of accuracy
double
Floating-point numbers in the range of ±1.7× to ±1.7×10308 , with 15 digits of accuracy
Integer Data Types
Floating-Point Data Types

50. 4. Primitive Data Types (Cont’d)
General format of a variable declaration
DataType VariableName;
DataType : name of the data type
VariableName : name of the variable
Examples:
byte inches;
int speed;
short month;
float salesComission;
double distances;

51. 4. Primitive Data Types (Cont’d)
Combining variables of the same data type
int length;
int width;
int area;
int length, width, area;

52. Integer Literals Do not embed commas in numeric literals.
int number;
number = 1,257,649; //ERROR !
number = ;
We can force an integer literal to be treated as long
57 be treated as int value
57L, 57l be treated as long values

53. Floating-Point Literals
Java assumes floating-point literals such as 29.75, 1.76, … to be of double data type.
float number;
number = 25.5; //Error !
number = 25.5F;
number = 25.5f;

54. Scientific and E Notation
Floating-point literals can be represented in scientific notation.
47, ×104
Java uses E notation to represent values in scientific notation.
Decimal Notation
Scientific Notation
E Notation
247.91
2.4791×102
2.4791E2
7.2×10-4
7.2E-4
2,900,000
2.9×106
2.9E6

55. The boolean Data Type
The boolean data type allows us to create variables that hold one of two possible values:
true
false
Variables of boolean data type are useful for evaluation conditions that are either true or false.

56. The boolean Data Type (Cont’d)

57. The char Data Type The char data type is used to store characters.
A variable of the char data type can hold one character at a time.
Character literals
‘A’, ‘B’, ‘a’, ‘s’, …
Characters are internally represented by numbers (Unicode)
‘A’ : 65 ‘B’: 66 …

58. The char Data Type (Cont’d)
Characters and how they are stored in memory

59. The char Data Type (Cont’d)

60. The char Data Type (Cont’d)

61. Variable Assignment and Initialization
Using = assignment operator
The operand on the left side of the = operator must be a variable.
The value in right side of the = operator is assigned to the variable in left side.
int unitSold;
unitSold = 12;
12 = unitSold; //ERROR !

62. Variable Assignment and Initialization (Cont’d)
We may also assign values to variables as part of the declaration statement
int month = 2, days = 28;
int flightNum = 89, travelTime, departure = 10;

63. Variables Hold Only One Value at a Time
A variable can hold only one value at a time.
When we assign a new value to a variable, the new value replaces the variable’s previous contents.

64. 5. Arithmetic Operator There are three types of operators: Unary
Requires only a single operand
-5 -number (negative operator)
Binary
Requires two operands
Ternary
Requires three operands

65. 5. Arithmetic Operator (Cont’d)
Common operators
Operator
Meaning
Type
Example +
Addition
Binary
total = cost + tax; -
Subtraction
cost = total – tax; *
Multiplication
tax = cost * rate; /
Division
salePrice = original / 2; %
Modulus
remainder = value % 3;

66. Integer Division
When both operands of a division statement are integers, the statement will result in integer division.
The result of the integer division will be an integer.
double parts; double parts;
parts = 17 / 3; parts = 17.0 / 3;
parts is assigned the value 5.0
parts is assigned the value

67. Operator Precedence
Precedence of arithmetic operators (highest to lowest)
- (unary negation)
* / %
+ -
outcome = / 3 =
= 14

68. Operator Precedence (Cont’d)
Associativity of arithmetic operators
Operator
Associativity
- (unary negation)
Right to left
* / %
Left to right
+ -
Expression
Value
5 + 2 * 4
10 / 2 – 3
* 2 – 4
% 2 – 1
6 – 3 * – 1

69. Grouping with Parentheses
To force some operations to be performed before others
Expression
Value
(5 + 2) * 4
10 / (5 – 3)
* (6 – 2)
(4 + 17) % 2 – 1

70. The Math class Math class is a member of Java API. The Math.pow method
Rising a number to a power
result = Math.pow(4.0, 2.0); // 42
The Math.sqrt method
accepts a double value as its argument and returns the square root of the value.
result = Math.sqrt(9.0); //

71. 6. Combined Assignment Operators
The combined assignment operators combine the assignment operator with the arithmetic operators.
x += 5;
x = x + 5;
equivalent to
Add 5 to x
The resut is then assigned to x

72. 6. Combined Assignment Operators (Cont’d)
Example Usage
Equivalent To +=
x += 5;
x = x + 5; -=
y -= 2;
y = y – 2; *=
z *= 10;
z = z * 10; /=
a /= b;
a = a / b; %=
c %= 3;
c = c % 3;

73. 7. Conversion between Primitive Data Types
Before a value can be stored in a variable, the value’s data type must be compatible with the variable’s data type.
Java performs some conversions between data types automatically, but does not perform any conversion that can result in the loss of data;

74. 7. Conversion between Primitive Data Types (Cont’d)
int x; double y = 2.5; x = y; //ERROR ! Possible loss precision short y = 2; x = y; // OK

75. 7. Conversion between Primitive Data Types (Cont’d)
In assignment statements where values of lower-ranked data types are stored in variables of hight-ranked data types, Java automatically converts the lower-ranked value to the higher-ranked type. (widening conversion)
Primitive data type ranking
double Highest Rank
float
long
int
short
byte Lowest Rank
double x;
int y = 10;
x = y; //widening conversion

76. Cast Operators
A narrowing conversion is the conversion of a value to a lower-ranked type.
Narrowing conversions can cause a loss of data, Java does not automatically perform them.
The cast operator lets you manually convert a value, even if it is a narrowing conversion.

77. Cast Operators (Cont’d)
Cast operators are unary operators that appear as a data type name enclosed in a set of parentheses.
int x;
double y = 2.5;
x = (int)y; // x = 2;
cast operator

78. Cast Operators (Cont’d)
int pie = 10, people = 4; double piesPerPerson; piesPerPerson = pie / people; piesPerPerson = (double)pie / people; piesPerPerson = pie / (double)people; piesPerPerson = (double)(pie / people);
2.0
2.5
2.5
2.0

79. Mixed Integer Operations
With arithmetic operations on int, byte, and short variables:
Values of the byte or short data types are temporarily converted to int value.
The result will always be an int.
short x = 10, y = 20, z;
z = x + y; //causes an error
x + y results an int number

80. Other Mixed Mathematical Expressions
If one of an operator’s operands is a double, the value of the other operand will be converted to a double. The result of the expression will be a double.
If one of an operator’s operands is a float, the value of the other operand will be converted to a float. The result of the expression will be a float.
If one of an operator’s operands is a long, the value of the other operand will be converted to a long. The result of the expression will be a long.

81. 8. Creating Named Constants with final
The final keyword can be used in a variable declaration to make the variable a named constant.
Named constants are initialized with a value, and that value cannot change during the execution of the program

82. 8. Creating Named Constants with final (Cont’d)
amount = balance * 0.069;
final double INTEREST_RATE = 0.069;
amount = balance * INTEREST_RATE;
The Math.PI Named Constant
is assigned the value
is an approximation of the mathematical value pi.
area = Math.PI * radius * radius;
Interest rate

83. 9. The String Class
String literals are enclosed in double quotation marks.
“Hello World” “Joe Mahoney”
Java does not have a primitive data type for storing strings in memory.
The String class
Allows you to create objects for holding strings.
Has various methods that allow you to work with strings.

84. 9. The String Class (Cont’d)
Objects are created from classes.
Declare a variable of the String class
String name;
A class type variable does not hold the actual data item. It holds the memory address of the data item.
name is a class type variable, holds the memory address of a String object.
When a class type variable holds the address of an object, it is said that the variable references the object.
Class type variables are known as reference variables.

85. 9. The String Class (Cont’d)
Creating a String object
String name;
name = “Joe Mahoney”;
String object is created in memory with the value “Joe Mahoney” stored in it.
The address of that object is stored in the name variable.

86. 9. The String Class (Cont’d)
Class type variables
String name;
name = “Joe Mahoney”;
Primitive type variables
int number;
number = 25;

87. 9. The String Class (Cont’d)

88. 9. The String Class (Cont’d)
String provides numerous methods for working with strings.
To call a method means to execute it.
ReferenceVariable.method(arguments…)
String name;
name = “Tony Gaddis”;
int stringSize;
stringSize = name.length();
length method of String is called

89. A few String class methods
charAt(index)
index is an int value and specifies a character position in the string. The first character in the string is at position 0.
The method return the character at the index position.
length()
Returns the number of characters in the string.

90. A few String class methods
toLowerCase()
Returns a new string that is the lowercase equivalent of the string contained in the calling method.
toUpperCase()
Returns a new string that is the uppercase equivalent of the string contained in the calling method.

91. A few String class methods

92. 10. Scope Every variable has a scope.
A variable’s scope is the part of the program that has access to the variable.
Variables can not be accessed by statements that are outside the scope.
Variables that are declared inside a method are called local variables.

93. 10. Scope (Cont’d)
A local variable’s scope begins at the variable’s declaration and ends at the end of the method in which the variable is declared.

94. 10. Scope (Cont’d)
We can not have two local variables with the same name in the same scope.

95. 11. Comments Comments are notes of explanation.
Comments are parts of the program, but the compiler ignores them.
They are intended for people who may be reading the source code
Documented programs will make your life easier.

96. 11. Comments (Cont’d) Three ways to comment in Java
Single-line comments
Using two forward slashes //
Everything from // to the end of the line is ignored.
Multi-line comments
Multi-line comments start with /* and end with */.
Everything between /* and */ is ignored.

97. 11. Comments (Cont’d) Documentation Comments
Documentation comments can be read and processed by a program named javadoc.
The javadoc program reads Java source code files and generates HTML files that document the source code.
If the source code files contain any documentation comments, the information in the comments becomes part of the HTML documentation.

98. 11. Comments (Cont’d)
Any comment that starts with /** and ends with */ is considered a documentation comments.
Normally we write a documentation comment
before a class header, giving brief description of the class
before a method header, giving brief description of the method.
Run javadoc
javadoc SourceFile.java

99. 11. Comments (Cont’d) Generating javadoc in eclipse
Project \Generate Javadoc …
Enter Javadoc command
C:\Program Files\Java\jdk1.6.0_10\bin\javadoc.exe
Use standard doclet

100. 12. Programming Style
Programming Style refers to the way a programmer uses Spaces, Indentations, Blank lines, Punctuations to arrange a program’s source code.
This program is syntactically correct and is very difficult to read:

101. 12. Programming Style (Cont’d)

102. 12. Programming Style (Cont’d)
A common programming style is to indent all lines inside a set of braces
To handle statements that are too long to fit in one line:
Extra spaces are inserted at the beginning of statement’s second, third … lines, which indicate that they are continuations.

103. 12. Programming Style (Cont’d)

104. 12. Programming Style (Cont’d)
Declaration of multiple variables of the same type with a single statement
To write each variable name on a separate line with a comment explaining the variable’s purpose.
int fahrenheit, //Fahrenheit temperature
centigrade, //Centigrade temperature
kelvin; //Kelvin temperature

105. 13. Reading Keyboard Input
System.in is an object
Standard input device
Is used to read keystrokes
Reads input only as byte values
Is not very useful because programs normally requires values of other data types
Objects of the Scanner class can be used to read input from the keyboard.
Reads input from a source such as System.in
Provides methods to retrieve the input formatted as primitive values or strings.

106. The Scanner object
The Scanner class is not automatically available to Java programs.
Using import statement to tell the compiler where in the Java library to find the Scanner class
import statement must be placed near the beginning of the file, before any class definition
import java.util.Scanner;

107. The Scanner object (Cont’d)
Create the Scanner object and connect it to the System.in object.
Scanner keyboard;
keyboard = new Scanner(System.in);
new
a Java keyword
is used to create an object in memory

108. The Scanner object (Cont’d)
Scanner keyboard = new Scanner(System.in);
This declares a variable named keyboard . The variable can reference an object of the Scanner class.
This creates a Scanner object in memory. The object will read input from System.in
The = operator assigns the address of the Scanner object to the keyboard variable.

109. The Scanner object (Cont’d)
The Scanner class has methods for reading strings, bytes, integers, long integers, short integers, float and doubles.
int number;
Scanner keyboard;
keyboard = new Scanner(System.in);
System.out.println(“Enter an integer:”);
number = keyboard.nextInt();

110. The Scanner object (Cont’d)
Some of the Scanner methods
byte nextByte():
returns input as a byte.
double nextDouble():
returns input as a double.
float nextFloat():
returns input as a float.
int nextInt():
returns input as an int.

111. The Scanner object (Cont’d)
String nextLine():
returns input as a String.
long nextLong():
returns input as a long.
short nextShort():
returns input as a short.

112. The Scanner object (Cont’d)
Problem: User’s gross pay
Write a Java program to calculate the gross pay of a user. The program allows user to enter user’s name, hours worked, pay rate, and display the user’s gross pay on the console.

113. User’s gross pay Display “What is your name?”.
Input user’s name. → Store in a variable
Display “How many hours did you work?”.
Input hours. → Store in a variable
Display “How much do you get paid per hour?”.
Input rate. → Store in a variable
Calculate the user’s gross pay and store in a variable
Display user’s name and gross pay

114. User’s gross pay

115. User’s gross pay

116. Reading a Character
The Scanner class does not have a method for reading a single character.
To read a single character using the Scanner class:
Use the nextLine method of the Scanner class to read a string from the keyboard.
Use the charAt method of the String class to extract the first character of the string.

117. Reading a Character (Cont’d)
String input; //To hold a line of input
char answer; // To hold a single character
Scanner keyboard;
keyboard = new Scanner(System.in);
System.out.println(“Are you having fun? (Y/N)”);
input = keyboard.nextLine(); // Get a line of input
answer = input.charAt(0); // Get the first character

118. Mixing Calls to nextLine with calls to Other Scanner Methods
When we call one of the Scanner class’s methods to read a primitive value, then call the nextLine method to read a string → The string is not read
Because the Scanner class’s methods to read a primitive value left a newline character in the keyboard buffer.

119. Mixing Calls to nextLine with calls to Other Scanner Methods

120. Mixing Calls to nextLine with calls to Other Scanner Methods

121. Mixing Calls to nextLine with calls to Other Scanner Methods
To fix the problem
Insert the nextLine method to consume, or remove, the newline character that remains in the keyboard buffer.

122. 14. Dialog Boxes
A dialog box is a small graphical window that displays a message or requests input.
The JOptionPane class allows you to quickly display a dialog box
Display dialog: To display a message
Input dialog: To request input

123. Display Message Dialogs
The showMessageDialog method is used to display a message dialog
JOptionPane.showMessageDialog(null, “Hello World”);

124. Display Input Dialog
The showInputDialog method is used to display an input dialog
String name;
name = JOptionPane.showInputDialog(“Enter your name”);
The name variable will reference the string value entered in the text field.
Text field

125. Converting String Input to Numbers
Because the showInputDialog method always returns the user’s input as a String, even if the user enters numeric data
We must convert the input string to a numeric value if the string represents numeric data.

126. Converting String Input to Numbers (Cont’d)
Methods for converting strings to numbers
Byte.parseByte
Convert a string to a byte
byte num;
Num = Byte.parseByte(str);
Double.parseDouble
Convert a string to a double

127. Converting String Input to Numbers (Cont’d)
Float.parseFloat
Convert a string to a float
Integer.parseInteger
Convert a string to an int
Long.parseLong
Convert a string to a long
Short.parseShort
Convert a string to a short

128. PayrollDialog
Write the Payroll program using dialogs to get user’s input and display user’s information.

129. PayrollDialog

130. PayrollDialog