Scientech Easy How to create object in Java with example & programs | Scientech Easy

Monday, January 7, 2019

How to create object in Java with example & programs

Welcome to the online Java tutorial. In this chapter, we will learn How to create an object in Java with some simple example and programs which will be helpful to understand the concept of an object. 

For which purpose we create an object in Java

We create an object in Java applications because of three reasons. They are as follows:
1. Since Java is purely object-oriented programming language. So Everything is done in the form of objects only. Therefore, objects are required in the Java programming language.
2. To store data temporarily in Java application, we require to create an object. The object provides temporary storage for our data.
3. To access members of any particular class, we have to create an object of the respective class. Whenever we create an object in any program, the Object reference variable is automatically generated. By using this object reference variable only, we can access the members of a particular class. The reference variable must have reference value. The Dot(.) operator gives you to access an object's state and behavior (instance variables and methods).  These are three reasons for which we create objects in Java programs.   

How to create an object in Java

There are several ways to create an object of the class in Java. They are:
a. Using the new keyword
b. Using Class.forName
c. Using Clone.
d. Using Object Deserialization.
e. Using ClassLoader.
In this chapter, we will learn using the new keyword to create the object of the class and another way we will learn one by one in the next tutorial.

By using the new keyword
It is the most common and straightforward way to create an object in Java programming. It is very simple and easily understandable to create an object of the class in the program. 
new is a special keyword which is used to create an object of the class. It allocates the memory to store the objects whose type is specified by a constructor and then calls the constructor to initialize the object which is stored in the heap(a region of memory for storing object).  When the constructor ends, new return memory addresses to the object so that it can be accessed from anywhere in the application. See below image.
Java Object Example,  How many ways to create object of the class in Java
How to create an object of the class
The general form of a statement is
ClassName object_Reference_variable_name=new ClassName();
Now consider the example to an object/instance of a class College.
      College cg=new College();
      College Name of the class.
         cg       Object reference variable which stores the address of the object in the stack memory.
      new      keyword that stores the object in the heap memory.
  College() Constructor of the class.
        =         The equal sign(=) is an assignment operator. It simply says to take the object created by new keyword and assign it to the object reference variable.
By using this method, we can call the no-argument constructor as well as parameterized constructor.
For example:
    Student st=new Student(); // It will call default constructor.
    School sc=new School("DEEP"); // It will call Parameterized constructor.

Program Source Code: Let's take a very simple program step by step. 
    package scientech; // Step 1: Create a class with the name HelloJava. public class HelloJava { // Step 2: Declare the constructor with the class name. This constructor is a default. HelloJava(){ // It will print the message on the console. System.out.println("Hello Java"); } // Step 3: Declare a method and Print any message which you want. void display(){ System.out.println("Welcome to online Java tutorial point. "); } // Step 4: Declare the main method. This method is static. public static void main(String[] args) { // Step 5: Create an object of the class with the object reference variable 'obj'. HelloJava obj=new HelloJava(); // It will call default constructor as object created. // Step 6: Now call the method to print the output on the console using object reference variable 'obj'. obj.display(); } }
    Output: Hello Java Welcome to online Java tutorial point.
You follow all the above steps to make your program easy and keep all steps in mind. 

What is void

The void is a keyword which indicates that this method does not provide or return any data back to the class of an object.
Now let's take one more example for practice.
Program source code 2: In this program, we will calculate the sum of two numbers. you follow all the above steps.
    package scientecheasy; public class Sum { // Declare instance variables. int a; int b; // Declare a default constructor and initialize the value of variables. You can also initialize directly to the variables. This is another way to initialize the value of variables. Sum(){ a=50; b=20; } // Declare a method and write the logic of add the numbers. void display(){ int sum=a+b; System.out.println("Sum of two numbers: " +sum ); } public static void main(String[] args) { // Create an object of the class and call the method using reference variables to print output on the console. Sum sm=new Sum(); sm.display(); } }
    Output: 70

Final words:
I hope that this article will help to understand the topic How to create an object in Java for example and programs. We hope that this article has covered almost all important concepts related to this topic. We always try to understand you in an easy way. In the next tutorial, we will learn different ways to initialize the objects.

Next ➝ Object Declaration and Initialization