Java Short Review

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Java Short Review
Source http//java.sun.com/docs/books/tutorial
15 Jan 2004
Adianto Wibisono
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Outline

• General Concepts
• Object, Messages, Class, Inheritance, Interfaces
• Class Structure
• Class Declaration, Class Body, Constructor,
  Member Variables, Methods, Access Control,
  Instance Class Members
• Examples Walkthrough
• Hello World, Other simple examples describing the
  concepts.
• Practical Information
• Compiling, environment setup (CLASSPATH), using
  existing packages, Java tools

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General Concept

• Object Oriented Programming Overview
• What is object ?
• How object interact ?
• What is a class ?
• What is inheritance ?
• What is interface ?

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What is Object ?

• Taken from real world objects, which has states
  and behaviour
• State lt-gt Data/Information ?Variable
• Behaviour lt-gt Function ?Methods
• Definition 
• An object is a software bundle of variables and
  related methods.

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Objects
Bycicle Object
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Object Interaction Message passing
Receiver/Target Object
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Class

• Definition 
• A class is a blueprint, or prototype, that
  defines the variables and the methods common to
  all objects of a certain kind.

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Class Instances a.k.a Objects
Class
Instance/Object
Instance/Object
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Inheritance
Superclass
Subclasses
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Inheritance

• Subclasses provide specialized behaviors from the
  basis of common elements provided by the
  superclass.
• Enable reuse of the code in the superclass.
• Superclasses can be abstract classes that define
  "generic" behaviors
• Not all members of this abstract classes need to
  be implemented, it will be done on the subclasses

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Interface

• Definition
• A Java(TM) programming language keyword used to
  define a collection of method definitions and
  constant values. It can later be implemented by
  classes that define this interface with the
  "implements" keyword

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Interface

• Usage
• 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

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Class Structure

• Structure Outline
• Class Declaration
• Class Body
• Constructor
• Member Variables
• Instance Class Members
• Implementing Method
• Control Access

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Structure Outline
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Class Declaration
Required
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Class Body

• Body of a class contains
• Constructors for initializing new objects
• Declaration of Variables providing the state of
  the class and its objects
• Methods to implement the behaviour of the class
  and its objects
• Ocassionally a finalize method for cleaning up an
  object

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Constructor

• Has the same name as the class
• Can have many constructor with different
  parameter list, but the same name (overloading)
• Automatically invoked when you create an object
  with operator new

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Member Variables
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Instance vs Class Member

• Instance variable/method ? Belong specifically to
  the instance
• Class variable/method ? Belong to the class (all
  instances has it)
• Declared as static variables

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Instance vs Class Member
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Implementing Method
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Control Access of a Method/Member Variable

• Private
• accessible only to the class in which it is
  defined
• Protected
• Accessible to the class itself, subclasses, and
  classes in the same package
• Public
• Any class, Any Package has access to this method
  / member variable

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Example Walkthrough

• Hello World
• Bycicle Class
• Using Bycicle class
• Inheritance example
• Interface example
• Collection
• Exception Handling

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Hello World

• /
• The HelloWorldApp class implements an
  application that
• displays "Hello World!" to the standard
  output. /
• public class HelloWorldApp
• public static void main(String args)
• // Display "Hello World!"
• System.out.println("Hello World!")

Class Variable/Member
Instance Method
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Bycicle Class

• public class Bycicle
• protected int speed
• protected int gear
• Bycicle()
• speed0
• gear1
• public void changeGear(int newGear)
• gear newGear
• public void increaseSpeed(int deltaSpeed)
• speed deltaSpeed
• public void printState()
• print(Bycicle speed is speed in
  gear gear)

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Using Bycicle Class

• public class UseBike
• public static void main(String args)
• Bycicle bike new Bycicle()
• bike.increaseSpeed(10)
• bike.changeGear(2)
• bike.printState()

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RacingBike Inherit Bycicle

• public class RacingBike extends Bycicle
• public void boostSpeed()
• speed speed10

Specialized function specific to this subclass
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Using RacingBike Class

• public class UseRacingBike
• public static void main(String args)
• RacingBike bike new RacingBike()
• bike.increaseSpeed(10)
• bike.changeGear(2)
• bike.printState()
• bike.boostSpeed()
• bike.printState()

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Interface TravelingObj

• public interface TravelingObj
• public int getDistance(int time)
• public void printDistance(int time)

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Sprinter Implements TravelingObj

• public class Sprinter implements TravelingObj
• protected int speed
• protected String name
• Sprinter (String name, int speed)
• this.name name
• this.speed speed
• public int getDistance(int time)
• int distance time speed
• return distance
• public void printDistance(int time)
• System.out.println(Distance travelled so far by
  name is time speed)

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Sprinter Bike treated as the TravelingObj

• public class UseTravelingObj
• public static void printDistance(TravelingObj
  obj)
• obj.printDistance(10)
• public static void main(String args)
• Bycicle bike new Bycicle()
• Sprinter ali new Sprinter("Ali baba",
  10)
• printDistance(ali)
• printDistance(bike)

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Use Collection
dont reinvent the wheel.

• import java.util.
• public class Sort
• public static void main(String args)
  List l Arrays.asList(args) Collections.sort(l
  ) System.out.println(l)

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Sample Exception Handling

• class ErrorTest
• public static void main(String args)
• int arrInt new int20
• int i 0
• for (i 0 i lt 20 i)
• arrInti (int)(Math.random()100)
• try
• for (i 0 i lt 21 i)
• System.out.println("Value at " i "
  " arrInti)
• catch (ArrayIndexOutOfBoundsException e)
• System.out.println("Index out of bounds at
  index " i)

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Practical Information

• How to compile
• About classpath
• About Packages
• Java tools