Thinking Object and Classes

Class for Object

– Class is a template of the object, which defines the properties of objects, and provides constructors to create objects and methods to manipulate objects. 
– Object is a representation of the class. 
– Many objects that can be created using only a single class.  
– An object of the class have: 
Unique identity.
State – data field, properties.
Behavior – one or a set of method or function.
– Example : 
Class : Circle
Data fields : Radius
Methods : getArea
– Use the new operator to create objects and operator dot (.) To access the member object
– Example : 
Circle obj = new Circle();
 System.out.println(“area radius of the circle is ” + obj.getArea());



– Used to create objects
– First flight at the time the object was created using the new operator.
– has the same name with its class name.
– there is no return type nor the data type void.


Access Modifier

•Private : hide the class members so not accessible from outside the class
•Protected : allows members of the class can be accessed by the class or its derivatives in the classroom several similar packages.
•Public : allows the member class can be accessed by other classes class
•Package : used to organize classes. If the class that was created without using the package statement, the class will be placed in the default package. 



•Ability of objects
•In a programming language commonly known as a function / procedure
•Specification of header method :
  modifier return_value_type method_name(parameters){
  // Function contain
•Passing parameter by value is sending the value of a function that is in a class.
•A function allowing for the return value. Only void that does not return value from method. 
•A function will return the value in accordance with a data type functions. 

•Advantage of Method :

– Reusable.
Function can be used to reduce repetitive coding and the same coding can be used repeatedly by invoking the name of the function and can be used in other programs.
– Modularize.
Function makes the code into modules, so easy to search its mistakes and improve the quality of the program.
– Maintainable.
Easy to maintain. 


Overloading Method

•Have two or more names for the same function in a class with a sequence of different parameters.

public class TestOverloading{
public static int max( int a, int b, int c ){
if ( a > b )
return a;
return b;
  public static double max( double a, double b )
  if ( a > b )
  return a;
 return b;
public static double max( double a, double b, double c )
return max( max( a , b ) , c );


Abstract Method

•Dummy Code Method.
•Always be defined in abstract class.
•Abstract Class : Classes which are declared abstractly, can not be real, but can be used in subclasses.
•No implementation.
•Has no content of coding in the function
•End in a semicolon (;)
– Example :
public abstract class Circle{
  private double radius;
  public void setRadius ( double x ){
  radius = x;
  public abstract double getArea(); // Abstract method which return value type double
  public abstract void setRadius(); // Abstract method without returning of value And Overloading method


Static Variables and Static Methods

•Variable radius in class Circle is an instance variable
•If you want to use all of data of the entire event (instance) in a class, use static variables.
•Static Variables store value in local memory.
•Static Methods can be called without creating objects from the class. 
– Example :
public class Circle{
private double radius;
private static int numberofObject = 0;  //static variable
public static int getArea() { //static method
return numberofObject++;



•Used by all objects in class
•Must be declared with the keywordfinal static
 – Example :
PI constant in class Math
final static double PI = 3.14159265358979323846;


Inner Class

•Known as nested class.
•Defined in a class called Outer Class.
•Can access all class members which has been defined in the Outer Classes
•Create a program to be simple and concise
•Can be declared with access modifier
•Can be declared with static variables.
•A static inner class could not be accessed by non-static member from Outer Class

•Example for Inner Class :
public class OuterClass{
  private int data;
  public void m()   //functions that exist in the outer class
  //an inner class which exist in the outer class
  class InnerClass
public void mi()  //function that exist in inner class
data++;  //could directly access the outer class member


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