1. Java Tutorial Mr.Arun Kumar.P, Asst.Proff.,ISE Dept., JNNCE, Shimoga
4th Sem ISE, B Sectionp
8th March and 7th April 2017p 1

2. Object-Oriented Programming

3. Different Programming Paradigms
Functional/procedural programming:
program is a list of instructions to the computer
Object-oriented programming
program is composed of a collection objects that communicate with each other
flexibility, easing changes to programs
easier to learn
simpler to develop, maintain and analysize

4. Main Concepts
Object
Class
Inheritance
Encapsulation

5. Objects identity – unique identification of an object
attributes – data/state
services – methods/operations
supported by the object
within objects responsibility to provide these services to other clients

6. Class “type” object is an instance of class
class groups similar objects
same (structure of) attributes
same services
object holds values of its class’s attributes

7. class <ClassName>{
attributes/variables;
Constructors();
methods(); }

8. Instance is an Object of a class which is an entity with its own attribute values and methods.
Creating an Instance
ClassName refVariable;
refVariable = new Constructor(); or
ClassName refVariable = new Constructor();

9. Encapsulation
Separation between internal state of the object and its external aspects
How ?
control access to members of the class
interface “type”

10. Java Java is an object-oriented language, with a syntax similar to C
Structured around objects and methods
A method is an action or something you do with the object
Avoid those overly complicated features of C++:
Operator overloading, pointer, templates, friend class, etc.

11. Why Java ? Portable Easy to learn
[ Designed to be used on the Internet ]

12. Intro to Java Java programming language Java virtual machine (JVM)
The one we use to write our program
Compiled to byte code of JVM
Java virtual machine (JVM)
Java interpreter – interpret the compiled byte code
Software simulated CPU architecture
Cross-platform: support Linux, Windows, PalmOS…etc.
Java runtime environment (JRE)
Predefined set of java classes available to use
Core Java APIs – basic utilities, I/O, graphics, network…

13. JVM JVM stands for Java Virtual Machine
Unlike other languages, Java “executables” are executed on a CPU that does not exist.

14. Platform Dependent gcc machine code OS/Hardware Platform Independent
myprog.exe
myprog.c
machine code
C source code
OS/Hardware
JVM
bytecode
Java source code
myprog.java
javac
myprog.class
OS/Hardware
Platform Independent

15. Bottom line: slow but safe
Not suitable for high-performance computation
Scientific computation, games, OS kernel
Compiled to byte codes of JVM, not native machine language instructions
New release of Java is improving the speed a lot
Just-in-time (JIT) compiler: convert byte codes to native machine language on the fly
Very safe
No pointer
Automatic garbage collection
Check array access bound

16. Hello World! File name: Hello.java
/* Our first Java program – Hello.java */
public class Hello {
//main()
public static void main ( String[] args ) {
System.out.println( "hello world!" ); }
Command line arguments
Standard output, print with new line

17. Hello World Hello.java ( compilation creates Hello.class )
class Hello {
public static void main(String[] args) {
System.out.println(“Hello World !!!”); } }
C:\javac Hello.java
C:\java Hello
( compilation creates Hello.class )
(Execution on the local JVM)

18. About class Fundamental unit of Java program
All java programs are classes
Each class define a unique kind of object ( a new data type)
Each class defines a set of fields, methods or other classes
public: modifier. This class is publicly available and anyone can use it.

19. What is class? Class introduces a new data type
A class describes a set of objects that have identical characteristics (data elements) and behaviors (methods).
Existing classes provided by JRE
User defined classes
Once a class is established, you can make as many objects of it as you like, or none.

20. Data Abstraction Data Abstractions organize data. StudentType
Name (string)
Marks (num)
Grade (char)
Student Number (num)

21. Behavioral Abstraction
Behavioral Abstractions combine procedural and data abstractions.
Data State
Enqueue
Is Full
Is Empty
Dequeue
Initialize
Queue Object

22. Simple example: class Person
A Person has some attributes
The class defines these properties for all people
Each person gets his own copy of the fields
Attributes = properties = fields

23. Class Person: definition
String name;
int height; //in inches
int weight; //in pounds
public void printInfo(){
System.out.println(name+" with height="+height+", weight="+weight); }
class ClassName{ /* class body goes here */ }
class: keyword

24. Class Person: usage Person ke; //declaration
ke = new Person(); //create an object of Person
ke.name= “Ke Wang”; //access its field
Person sal = new Person();
sal.name=“Salvatore J. Stolfo”;
ke.printInfo();
Sal.printInfo(); // error here??

25. Class Person Name: Ke Wang height: 0 weight: 0 ke
Name: Salvatore J. Stolfo
height: 0
weight: 0
sal

26. Things to notice Java is case sensitive
whitespace doesn’t matter for compilation
File name must be the same as one of the class names, including capitalization!
At most one public class per file
If there is one public class in the file, the filename must be the same as it
Generally one class per file

27. Things to notice Java is case sensitive
whitespace doesn’t matter for compilation
File name must be the same as one of the class names, including capitalization!
At most one public class per file
If there is one public class in the file, the filename must be the same as it
Generally one class per file

28. What is an object? Object is a thing
An object has state, behavior and identity
Internal variable: store state
Method: produce behavior
Unique address in memory: identity
An object is a Instance of a class

29. More sophisticated Default C’tor Copy C’tor class Kyle {
private boolean kennyIsAlive_;
public Kyle() { kennyIsAlive_ = true; }
public Kyle(Kyle aKyle) {
kennyIsAlive_ = aKyle.kennyIsAlive_; }
public String theyKilledKenny() {
if (kennyIsAlive_) {
kennyIsAlive_ = false;
return “You bastards !!!”;
} else {
return “?”;
public static void main(String[] args) {
Kyle k = new Kyle();
String s = k.theyKilledKenny();
System.out.println(“Kyle: “ + s);
Default C’tor
Copy C’tor

30. More sophisticated Default C’tor Copy C’tor class Kyle {
private boolean kennyIsAlive_;
public Kyle() { kennyIsAlive_ = true; }
public Kyle(Kyle aKyle) {
kennyIsAlive_ = aKyle.kennyIsAlive_; }
public String theyKilledKenny() {
if (kennyIsAlive_) {
kennyIsAlive_ = false;
return “You bastards !!!”;
} else {
return “?”;
public static void main(String[] args) {
Kyle k = new Kyle();
String s = k.theyKilledKenny();
System.out.println(“Kyle: “ + s);
Default C’tor
Copy C’tor

31. Results javac Kyle.java ( to compile ) java Kyle ( to execute )
Kyle: You bastards !!!

32. Access Control public member (function/data) protected private
Can be called/modified from outside.
protected
Can be called/modified from derived classes
private
Can be called/modified only from the current class
default ( if no access modifier stated )
Usually referred to as “Friendly”.
Can be called/modified/instantiated from the same package.

33. Methods allows to reuse a sequence of statements
Inheritance allows to reuse classes by deriving a new class from an existing one
The existing class is called the parent class, or superclass, or base class
The derived class is called the child class or subclass.
The child class inherits characteristics of the parent class(i.e the child class inherits the methods and data defined for the parent class 33

34. Inheritance Generalization and Specialization (Cntd...)
- subclass inherits attributes and services from its superclass
- subclass may add new attributes and services
- subclass may reuse the code in the superclass
- subclasses provide specialized behaviors (overriding and dynamic binding)
- partially define and implement common behaviors (abstract)

35. Inheritance (Cntd...) Base Derived
class Base {
Base(){}
Base(int i) {}
protected void foo() {…} }
class Derived extends Base {
Derived() {}
Derived(int i) {
super(i); …
super.foo();
(Cntd...)
Base
Derived
As opposed to C++, it is possible to inherit only from ONE class.
Pros avoids many potential problems and bugs.
Cons might cause code replication

36. Inheritance In Java, all methods are virtual : (Cntd...) class Base {
void foo() {
System.out.println(“Base”); }
class Derived extends Base {
System.out.println(“Derived”);
public class Test {
public static void main(String[] args) {
Base b = new Derived();
b.foo(); // Derived.foo() will be activated

37. Polymorphism Inheritance creates an “is a” relation:
(Cntd...)
Inheritance creates an “is a” relation:
For example, if B inherits from A, than we say that “B is also an A”.
Implications are:
access rights (Java forbids reducing access rights) - derived class can receive all the messages that the base class can.
behavior
precondition and postcondition

38. Inheritance (3) - Optional
(Cntd...)
class classC extends classB {
classC(int arg1, int arg2){
this(arg1);
System.out.println("In classC(int arg1, int arg2)"); }
classC(int arg1){
super(arg1);
System.out.println("In classC(int arg1)");
class classB extends classA {
classB(int arg1){
System.out.println("In classB(int arg1)");
classB(){
System.out.println("In classB()");

39. Inheritance (3) - Optional
(Cntd...)
class classA {
classA(int arg1){
System.out.println("In classA(int arg1)"); }
classA(){
System.out.println("In classA()");
class classB extends classA {
classB(int arg1, int arg2){
this(arg1);
System.out.println("In classB(int arg1, int arg2)");
classB(int arg1){
super(arg1);
System.out.println("In classB(int arg1)");
} class B() { System.out.println("In classB()"); }

40. (Cntd...)
Inheritance relationships are often shown graphically in a class diagram, with the arrow pointing to the parent class
Animal
weight : int
+ getWeight() : int
Bird
+ fly() : void 40

41. In Java, class “Object” is the base class to all other classes
(Cntd...)
In Java, class “Object” is the base class to all other classes
If we do not explicitly say extends in a new class definition, it implicitly extends Object
The tree of classes that extend from Object and all of its subclasses are is called the class hierarchy
All classes eventually lead back up to Object
This will enable consistent access of objects of different classes.

42. Abstract
abstract member function, means that the function does not have an implementation.
abstract class, is class that can not be instantiated.
AbstractTest.java:6: class AbstractTest is an abstract class.
It can't be instantiated.
new AbstractTest(); ^
1 error
NOTE:
An abstract class is not required to have an abstract method in it.
But any class that has an abstract method in it or that does
not provide an implementation for any abstract methods declared
in its superclasses must be declared as an abstract class.
Example

43. Abstract - Example package java.lang; public abstract class Shape {
public abstract void draw();
public void move(int x, int y) {
setColor(BackGroundColor);
draw();
setCenter(x,y);
setColor(ForeGroundColor); }
package java.lang;
public class Circle extends Shape {
public void draw() {
// draw the circle ... }

44. Interface Interfaces are useful for the following:
Capturing similarities among unrelated classes without artificially forcing a class relationship.
Declaring methods that one or more classes are expected to implement.
Revealing an object's programming interface without revealing its class.

45. Interface Example abstract “class”
Helps defining a “usage contract” between classes
All methods are public
Java’s compensation for removing the multiple inheritance. You can “inherit” as many interfaces as you want.
Example
* - The correct term is “to implement”
an interface

46. Interface interface IChef { void cook(Food food); }
interface BabyKicker {
void kickTheBaby(Baby); }
interface SouthParkCharacter {
void curse(); }
class Chef implements IChef, SouthParkCharacter {
// overridden methods MUST be public
// can you tell why ?
public void curse() { … }
public void cook(Food f) { … } }
* access rights (Java forbids reducing of access rights)

47. When to use an interface ?
Perfect tool for encapsulating the classes inner structure. Only the interface will be exposed