1. Object-Oriented Programming with Java
Object-Orientation and Java
Lecture 1

2. Object-Orientation & Java
Contents
Getting Started
A Little Bit of Syntax
Differences between C and Java
Object-Oriented Programming in Java

3. Getting Started Goto: Download the Java Software Development Kit (SDK)
Download the Java Software Development Kit (SDK)
Its free!
Download the Documentation
Also free! (
Buy JAVA In a Nutshell, by David Flanagan, Publ. O’Rielly
It’ll cost you, sorry!

4. File extensions in Java
Source
.class
javac (compiler)
Byte code
JVM
Java Virtual Machine
Any Hardware (that supports the JVM)

5. What you get in the JDK appletviewer For running Applets javac
Compiles .java  .class
java
Interprets a Java Class
classes.zip
The system provided classes
src.zip
Complete source for standard classes
javadoc
Generates Java HTML documents …

6. Object-Orientation & Java
Contents
Getting Started
A Little Bit of Syntax
Differences between C and Java
Object-Oriented Programming in Java

7. { Defining a Class Account public class Account { public int number;
public double balance;
public void credit(double x) {
// do some sums }
public void debit(double y) {
// do checking then sums {
members
number
balance
fields
credit_account
debit_account
methods

8. “Circle” Example public class Circle { } Circle radius circumference
area
public static final double PI = ;
public double radius;
public double circumference() {
return 2 * PI * radius; }
public double area() {
return PI * radius * radius;

9. The “Circle” class public class Circle { // A class field
public static final double PI= ; // A useful constant
// A class method: just compute a value based on the arguments
public static double radiansToDegrees(double rads) {
return rads * 180 / PI; }
// An instance field
public double r; // The radius of the circle
// Two instance methods: they operate on the instance fields
// of an object
public double area() { // Compute the area of the circle
return PI * r * r;
public double circumference() { // Compute the circumference
return 2 * PI * r;

10. The “main” method public class Circle {
public double r; // The radius of the circle
public double area() { // Compute the area of the circle
return PI * r * r; }
public double circumference() { // Compute the circumference
return 2 * PI * r;
public static void main(String[] args) {
int input = Integer.parseInt(args[0]);
Circle c = new Circle();
c.r = input;
double result = c.circumference();
System.out.println(result); }

11. Put “main” in a new class?
public class MakeCircle {
public static void main(String[] args) {
int input = Integer.parseInt(args[0]);
Circle c = new Circle();
c.r = input;
double circum = c.circumference();
System.out.println(circum);
double a = c.area();
System.out.println(a); }

12. An Association Circle radius circumference area MakeCircle main
creates instances of

13. File extensions in Java
Source
.class
javac (compiler)
Byte code
JVM
Java Virtual Machine
Any Hardware (that supports the JVM)

14. The Circle example C:\Java contains C:\>cd Java Circle.java and
MakeCircle.java
C:\>cd Java
C:\Java>javac Circle.java
C:\Java>javac MakeCircle.java
C:\Java now also contains
Circle.class and
MakeCircle.class
C:\Java>java MakeCircle 4
C:\Java>java MakeCircle 5

15. Object-Orientation & Java
Contents
Getting Started
A Little Bit of Syntax
Differences between C and Java
Object-Oriented Programming in Java

16. Differences No Preprocessor No Global Variables
No analogues of #define, #include, #ifdef
Constants are replaced by static final fields
No Global Variables
Avoids possibility of namespace collisions
We will see later how you can make a constant or variable globally accessible

17. Java vs. C Well-defined primitive type sizes No pointers
Removes this as a platform dependency
No pointers
Although Java Classes and Arrays are reference types, these references are “opaque”. No “address of” or “dereference” operators
This is not a handicap and eliminates an important source of bugs

18. Java vs. C Garbage Collection No goto statement
Objects are “tidied away” as soon as there are no further references to them
So, no need to explicitly manage memory
Eliminates memory leaks
No goto statement
Adds exception handling and labelled break and continue statements

19. Java vs. C Variable declarations anywhere Forward references
Java allows local variable definitions to be made anywhere in a method or block
Good practice to group them, though
Forward references
Methods can be invoked before they are defined (we’ll see why it is important to be able to do this)

20. Java vs. C Method overloading No struct and union types
Multiple methods can be defined with the same name, so long as they have different parameter lists
No struct and union types
No enumerated types
No bitfields
No typedef
No method pointers
No variable-length argument lists

21. Object-Orientation & Java
Contents
Getting Started
A Little Bit of Syntax
Differences between C and Java
Object-Oriented Programming in Java