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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());

Constructor

– 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.

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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. 

Methods

•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. 

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•A function will return the value in accordance with a data type functions. 
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•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;

else

return b;

  }

  public static double max( double a, double b )

{

  if ( a > b )

  return a;

  else

 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 StaticMethods

•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++;

  }

}

Constants

•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

 {

  //statement

  }

  //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

m();

  }

  }

}

One thought on “Thinking Object and Classes

  1. Good day! This is my 1st comment here so I just wanted to give a quick shout out and say I truly enjoy reading your blog posts. Can you recommend any other blogs/websites/forums that go over the same topics? Thanks for your time!

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