1. SSD1 – Introduction to Information Systems
Fundamentals of Java
Lecture 5

2. Data Types
Any objects in the real world have attributes. Attributes are characteristics of objects
Each attribute may take on specific kinds of information. In programming terms, we would say that an attribute has a specific data type
Data types – are the specific kinds of information

3. Data Types
One of the defining characteristics of a data type is its size in computer's memory.
Memory is measured in bits (binary digit).
A binary digit can take two values, 0 or 1.
A memory bit can store two states.
Bits can be combined to store information that is more meaningful.

4. Floating Point (from +-4.9E-324 to +-1.7976931348623157E+308)
Primitive Data Types
Type
Represents
Size
Example
boolean
Boolean value
(true or false)
1 bit
true
double
Floating Point (from +-4.9E-324 to E+308)
64 bits
3.14
int
Integer value
(from -2,147,483,648
to 2,147,483,647)
32 bits 6

5. Reference Data Types
Reference Types are more advanced types then primitive types
Every Java class is a reference type
Reference types range from very simple classes built solely from primitives to very complex types
One relatively simple reference type is the String class

6. Variables Variables are a fundamental building block of programming.
A variable represents a placeholder or container for information
A Java variable can be of certain type but every variable in Java must be of a certain type.
Strict typing also has an effect on memory use and allocation

7. Declaring Variables
Java, as a strongly typed language, requires the explicit designation of a data type when declaring a variable
This data type cannot change within the program
Similarly, if a Java program expects to receive data of a specific type, it will not accept data of any other type

8. Declaring Variables
Declaring a variable is specifying a data type and an identifier (a name) for that variable
Declaring a variable will allocate enough space in memory to store the variable's data type.

9. DataType variableName;
Declaring Variables
The generic declaration of a variable follows the following format
DataType variableName;
For example, the following are valid variable declarations
int age;
String name;
double salary;

10. Naming Variables Rules: Conventions
Identifiers can contain letters, underscores ( _ ), or the dollar sign ( $ )
Identifiers cannot start with a number
Identifiers may not contain spaces or other special characters or punctuation marks
Identifiers cannot be a Java keyword
Conventions
Identifiers should begin with a lower-case letter
Identifiers should be descriptive nouns, adjectives, or noun/adjective phrases

11. Valid Variable Identifiers Invalid Variable Identifiers
Naming Variables
Valid Variable Identifiers
Invalid Variable Identifiers x y
personalGreeting
_userID
$backgroundImage
double
3sisters
State Capitol

12. Using Variables Assignment String myStr; int x; int y;
The following assignments are possible
myStr = "This is a string";
x = 5;
y = 3; x = y;

13. Using Variables Initialisation String myStr = "This is a string";
Default Values
If a variable does not have a value assigned, Java helps by initializing the variable to a default value (whatever value is specified as the default for that type)
Reference variables are initialized to null which means that the variable does not refer to any object.

14. Using Variables
Scope

15. Arithmetic Operators and Expressions
int x = 100;
Operation
Operator
Example
Evaluates to:
Addition +
x + 5
105
Subtraction -
x - 5 95
Multiplication *
x * 2
200
Division for Quotient /
x / 2 50
Division for Remainder %
x % 2

16. Arithmetic Operators and Expressions
Casting
Casting is converting a value of one type to a similar value of another type at run time. To cast, specify within parentheses the type you want to cast to. The casting is acceptable for both primitive and reference types
int x;
int y;
y = (int) x * 0.5;

17. Arithmetic Operators and Expressions
Increment Operator
It is a shortcut in Java to increment the numeric value stored in a variable by one. The two statements below are equivalent:
age = age + 1;
++age;

18. Greater than or equal to
Relational Operators
Operator
Symbol
Greater than
>
Less than
<
Greater than or equal to
>=
Less than or equal to
<=
Exactly equal to ==
Not equal to !=
instance of
instanceof

19. Boolean Operators
Operator
Symbol
AND
&& OR ||
NOT !

20. AND Operator
The Boolean AND expression evaluates to true only when both the component Boolean expressions evaluate to true
Receives discount: (Is the customer a student) && (Is the age of the customer less than 24)

21. OR Operator
A Boolean OR expression evaluates to true only when either or both of the component Boolean expressions evaluate to true
Cannot play: (Is it raining) || (Is it snowing)

22. NOT Operator
If your height is NOT less than five feet you can join the police force
can join: !(height less than five feet)

23. Boolean Type and Boolean Variables
True
False

24. If-Else Statement

25. If-Else Statement Syntax if (booleanExpression) statement
The statement can be
a single statement,
a block of statements (enclosed by curly braces)
a null statement (just a semicolon)

26. If-Else Statement Examples if (isRaining) canPlay = false;
if (isRaining); // Does nothing.
if (order > 50.00)
{freeShipping = true;}
else
{freeShipping = false;}

27. If-Else Statement Examples if ((isStudent) && (age <= 24))
{discount = order_price * 0.1;}
else if (order_price > 50.00)
{discount = shipping;}
else {discount = 0;}

28. If-Else Statement Examples if ((isStudent) && (age <= 24))
{ discount = discount + order_price * 0.1;} 
if (order_price > 50.00)
{ discount = discount + shipping;}

29. Nested If-Else Statement
Examples
if ((isStudent) && (age <= 24)) {
if (order_price <= )
{discount = order_price * 0.1;}
else if (order_price > )
{discount = order_price * 0.15;} }
else if (order_price > 50.00)
{discount = discount + shipping;}

30. Iterations
Iteration allows the program to repeat statements until some condition is met.
Java offers three forms of iteration for the programmer to us.
With these forms of iteration or loops, programmers can create applications that repeat one or more Java statements as many times as required

31. The While-Loop
while (loop guard expression)
loopBody

32. The While-Loop Examples int i = 1; while (i < 5)
{out.println("value of i is " + i);        i = i+1;}
The while loop follows the "test then execute" pattern; it tests the value of i before printing it

33. The For-Loop
for (initialization; loopGuard; update) 
loopBody

34. The For-Loop Examples int i; for (i = 0; i < 5; i = i + 1)
{out.println("value of i is " + i); }
A loop body can also contain an empty statement
for (i = 0; i < 1000; i = i+1);

35. The Basics of Object-Oriented Programming
SSD1 – Introduction to Information Systems
The Basics of Object-Oriented Programming
Lecture 5

36. Classes Object-oriented programming is based on the notion of classes.
A class is a reference type which is used as a template for creating objects.
So the object is an instance of the class.
A person might be a class. And each of you is an instance of this class or an object of this class.

37. Classes
A class usually contains attributes and methods. An attribute is a characteristic of the class. A method is an action which is performed with the instance of that class.
int i; // variable of int type
Car y; // variable of Car type
(or object of the Car class)

38. Object Orientated Programs
Let’s take an example of corporate personnel to illustrate OOPs.
- Problem: Write a project proposal
- Personnel Involved: Vice President (VP) and Project Manager (PM)
We need two objects to model this task

39. Steps to Modelling Task
Object needed: One for Vice President and another for Project Manager
The class that these objects would belong to depends on behavior of these objects.
Hence consider attributes of the two objects:
Both objects have different tasks and responsibilities although both employees
Project Manager can be asked to prepare proposals, Vice President prepares financial data
One Vice President heads several teams, while a manager heads only one team

40. Steps to Modelling Task
Implies the two objects need two different classes
Details of tasks is as follows:
The VP requests PM to write a proposal. In response, PM starts the proposal and realizes financial data is needed from the VP.
PM asks VP for financial data. VP sends financial data to PM in response to this message.
PM completes the proposal with the financial data and other necessary information.

41. Attributes Attributes for the Vice President object:
Name
Department
Attributes for the Project Manager object:
Team

42. Messages
Message(s) from the Vice President object that the Project Manager object must respond to:
Write project proposal
Message(s) from the Project Manager object that the Vice President object must respond to:
Provide financial data

43. Steps to Modelling Task
Class representation according to attributes and functions discussed is illustrated in the diagram below.

44. Catfish Class. Attributes
...
private int row;
private int column;
private String imageFileName;
Identifiers of the attributes
Access to the attributes
Types of the attributes

45. Types of Access
Private. A class element with the private level can be accessed only within a class
Public. A class element with the public level can be accessed by objects of other types (from outside of the program)
Protected. A class element with the protected level can be accessed by objects of child classes.

46. Catfish Class. Methods getRow getColumn get methods getImage
swimRightIfPossible
swimLeftIfPossible
swimUpIfPossible
swimDownIfPossible
get methods

47. get Methods These methods are used to access the class attributes
For each attribute a get method must be defined

48. The type of value returned by the method
get Methods
public int getRow() {
return row; }
For instance, the getRow method allows another object to find out the row in the grid corresponding to the location of the Catfish object
The type of value returned by the method

49. Methods
The second set of methods attempts to modify a Catfish object to swim in a particular direction
swimRightIfPossible
swimLeftIfPossible
swimUpIfPossible
swimDownIfPossible

50. Method returns no value
Methods
public void swimRightIfPossible() {
// If the cell to the right is within bounds, move right.
if (column + 1 <= 10) {
column = column + 1; }
imageFileName = "/Catfish-right.gif";
Method returns no value

51. The Diagram of the Catfish Class

52. Writing Java Source Code
Java Compiler (javac.exe) is a program that translates a high-level language (Java) program into byte code (the result – the file with .class extension)
Java Virtual Machine (JVM) interprets the byte code into the machine code and executes this code as native code on the client machine. The JVM is the core of the Java platform.

53. Writing Java Source Code
Java Runtime Environment (JRE) contains JVM, class libraries, and other supporting files. JVM runs the program, and it uses the class libraries, and other supporting files provided in JRE.
If you want to run any java program, you need to have JRE installed in the system. 

54. Writing Java Source Code
Java Developer Kit (JDK) is a software bundle which contains tools needed to develop the Java programs, and JRE to run the programs.
The tools include compiler (javac.exe), Java application launcher (java.exe), the documentation generator (javadoc.exe), etc…

55. Writing Java Source Code

56. Writing Java Source Code
If you want to write your own programs in Java and to compile them you need JDK.
For running java programs, JRE is sufficient. 
In order to compile a Java program you need to write the following command in the command line
javac Catfish.java