Java10: Class and Object

Object is real life entity that has attributes and behaviors and has unique identity. In object oriented programming, a program is designed based on objects that take part in a system. 

 To use object in a program, first we have to define a class. Class is a blueprint that define how a object has to be created. Without a class, we can't create an object.

Defining a Class

To define a class

class ClassName{
    // attributes and behaviors.
}

The class keyword indicates the begining of the class definition. It is followed by the class name. As a convention, class name begins with capital letter and has no space. The the curly braket contains the attribute and behaviors of the class.

Example

class Circle{
    double radius;
    String color;

    double calculateArea(){
        double area;
        area = Math.PI * Math.pow(this.radius, 2);
        return area;
    }
    void info(){
        System.out.println("Color : " + this.color);
        System.out.println("Radius : " + this.radius);
    }
}

Creating the Object

To create an object, we need to use the new keyword. The syntax is: d

ClassName objectReference = new ClassName(parameters);
class CircleDemo{
    public static void main(String[] args){
        Circle cir1 = new Circle();
    }
}

The name of the class is Circle. and the object reference variable is cir1. Then, after the new keyword, we specify the name of the constructor, in this case it's Circle(). This will create the circle object and its reference is assigned to cir1.

Accessing property

To access the properties of the object, use the dot operator. For example

class CircleDemo{
    public static void main(String[] args){
        Circle cir1 = new Circle();

        cir1.radius = 3.5;

        double area = cir1.calculateArea();

        System.out.println("The area of the circle is " + area);
    }
}

Constructor

When we create an object, the constructor of the class is called. It is a special method whose main purpose is to create and initialize the object. A constructor has same name as the class name. All classes has constructor eventhough we don't provide one.

class ClassName{
    ClassName(parameters){
        // codes
    }
}

A constructor do not have return type as it does not return as value. The constructor initialize the object by assigning initial value to the attributes of the object.

class Circle{
    double radius;
    String color;

    Circle(double radius, double color){
        this.radius = radius;
        this.color = color;
    }

    double calculateArea(){
        double area;
        area = Math.PI * Math.pow(this.radius, 2);
        return area;
    }
    void info(){
        System.out.println("Color : " + this.color);
        System.out.println("Radius : " + this.radius);
    }
}

The constructor above allow us to create object as follows:

class CircleDemo{
    public static void main(String[] args){
        Circle cir1 = new Circle(3.5, "red");

        cir1.info();
    }
}

Output

Color: red
Radius : 3.5

A post by Cuber

Comments

Post a Comment

Popular posts from this blog

Drawing Simple Pie Chart

Image
To draw pie chart with 5 sectors. The program calculates the total of all the input given by user and find the angle in degrees to draw each sectors. When the program first loads, chart based on default values is painted by the program. User can edit the values in the text field and presses draw button to redraw the chart. Each time the draw button is pressed, new set of angle is calculated and repainted. I have attached the the sources for this program. It is simple and needs upgrades. Pie.java This class executed the program and initializes the components JTextField and JPanel to draw the chart. package coolApp.graphics; import java.awt.*; import java.awt.event.*; import javax.swing.*; public class Pie { JTextField a,b,c,d,e; JButton btnDraw; double total; JPanel contentPane; Pie(){ JFrame frame = new JFrame("Pie - CoolApps"); frame.setSize(500,500); contentPane = new JPanel(); contentPane.setLayout(new BorderLayout()); frame...
Read more

VB.net connecting to SQL Server

Connecting to SQL server 2014 from VB.Net 2017, read values from the database and display the data in windows form. Before begin to write this program, first we need to import SqlClient class. Imports System.Data.SqlClient Step 1 Create a sql connection object. This is to make connection to object. Dim conn As New SqlConnection() Step 2 Set the connection string to the sqlconnection object: conn.ConnectionString = connStr Road block The variable connStr is a connection string. Connection object need connection string to make connection to database. It has information like who providing the database, the name of the database and some security information. Dim connStr As String = "Data Source = ServerInstanceName;Initial Catalog=testDB;Integrated Security=True" Let's break down the connection string into the three main components. Dim provider As String = "ServerInstanceName;" Dim database As String = "Initial Catalog=testDB;" Dim ...
Read more

Setting up data set and display it

Before we display some data in DataGridView control in Visual Basic window we must create a data set. Data Set is an object that can hold data tables where all the data is stored in rows and columns. the first step is to create a table. Dim  dataTableObjectName as DataTable = New DataTable(tableName) this will create a table which is reference using the dataTableObjectName Example Dim userTable As DataTable = New DataTable("Users") Next step is adding columns to the table Dim column as DataColumn dataTableObjectName.Columns.Add (columnName, columnType) Example userTable.Columns.Add("userID", Type.GetType("System.Int.32")) ' adding second and third column userTable.Columns.Add("userName", Type.GetType("System.String")) userTable.Columns.Add("userContact", Type.GetType("System.String")) once we we columns in the table we can add row The rows contains records or the data for each user. dat...
Read more