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In this post for how to create an object in Java, we will discuss what is an object, how to store a Java object and popular ways for creating an object in Java. Java is an object-oriented programming language and in case of object-oriented language, we design a program using objects and classes. So, an object could be defined as the physical or logical entity both but classes could be given as logical entity only. Let us discuss objects in detail in the later sections.
What are Objects in Java?
An entity having state and behavior both is called as an object. For example, chair, car, pen, pencil, everything is an object around us. It can be either logical or physical both like tangible or intangible. Here are three popular characteristics of an object.
Let us understand the concept with the help of an example ahead. A pen is an object whose name is Reynolds, color is white, these are the states. The pen is used to write something, so the writing would be its behavior. And a unique identity is given by machine, so no need to discuss here. In simple words, an object could be defined as an instance of a class.
A class is a blueprint in Java that is used for creating objects. A class generally contains fields, methods, constructors, methods, blocks, nested classes etc. So, we can say that objects are instances or output of a class. Here are the following definitions for an object in Java –
One more term that can be used here is instance variable. This is a special variable that is created inside a class but outside of a method. These variables don’t take up the memory space during compile time but it is taking space during the runtime when an object or instance variable is created. This is the reason why it is named as an instance variable in Java. Let us see further how can you initialize an object in Java.
How to initialize an object in Java?
There are three popular techniques that can be used to initialize an object in Java.
1). Initialization through references
An object initialization means storing the data within an object. Let us understand the concept with the help of an example how to initiate objects through references below. This is possible to initiate multiple objects too through references and store the information together.
The output of this program would be given as –
2). Initialization through Methods
Take an example of student class where you need to create two objects for the same class and that can be further initiated through method. Here you could also display the state of a method by invoking any another method. Objects are generally stored in the heap memory area and the reference variables are used to refer objects allocated in the heap memory area. I hope you must have understood the difference between the reference variables and objects here.
3). Initialization through constructors
Constructors are also to initialize the new objects. The constructor has the same name as that classes, so they could always be identified quickly. Constructors don’t have any return type generally. For a compiler, this is easy to differentiate between class and constructor on the basis of number and type of arguments.
Keep in mind that every class has at least one constructor in Java. If there is no constructor defined by the programmer then it is given by the compiler as no argument constructor. We could say it as a default constructor in Java. Further, we can name as it as no-argument constructor too because it contains only one statement i.e. super (). Here, you can see that each Java class has one constructor that could be defined either directly or indirectly.
How to create an object in Java?
A class gives the blueprint for an object. So, basically, objects are derived from the class. Commonly, programmers use the new keyword to create an object in Java. Here are three major steps to follow when creating an object in Java.
Java developers are generating a plenty of objects daily but they are based on new and dependency management systems. For example, spring can be used to create objects here. Let us see the possible number of techniques here for creating an object in Java. There are total 5 ways as described by experts, let us discuss on each of them one by one further.
Using the new keyword
This is just the most popular and common technique for creating an object that is used by Java programmers worldwide. This is very simple and it allows us to call almost any constructor that we wanted to call. You could call even no-argument constructors too that does not contain any parameter.
With Class.newInstance () Method
We can use the newInstance () method of the class to create objects. This method will further call the no-argument constructor for creating an object. Here is the basic syntax of how to use this method for creating an object of the class.
With newInstance () method of constructor class
Similar to the previous technique, there is one newInstance () method in constructor class that can be used to create an object in Java. With this method, you could call parametrized or private constructors too whenever needed. Methods are called reflective ways for creating an object. This method is generally used internally and it can be used different frameworks like Springs, Hibernate, structs etc.
The basic syntax for using this method is given as below –
With the clone () Method
Every time we call a clone () method on an object, it will be creating a new object and copy all contents of previous objects into a new object. Keep in mind that creating an object with the clone method will not invoke any constructor. To clone an object, you should use the clone () method within it.
Cloning in Java is one of the most repeated topics in communities and it does have its drawbacks too. This is just a fabulous idea to copy the content of an existing object to the newer ones.
With Deserialization technique
Every time we serialize or deserialize an object then JVM will create the separate object for the same. In this technique too, Java does not use any constructor to invoke an object. For deserialization, an object should implement the Serializable interface in our class.
Good Practice – Use one type at one time
Mostly, we need multiple objects of a class in multiple methods. Creating a number of references together to create an object is not a good practice at all. Here, you should static reference variable and use whenever needed. In this case, the wastage of memory is always negligible. In case, there are a few objects that are not needed anymore then they would be destroyed by the garbage collector in Java. Here, the example is given below for a better understanding of the concept.
In the case of Inheritance in Java, we are using reference variables for storing the sub-class object. In this case, we should switch among subclass objects using the name of reference variables.
What are anonymous objects in Java?
Anonymous objects in Java are the special case where objects are initiated but never stored in a reference variable. They can be used for quick method calling. They are destroyed once calling to the method is complete. They are used frequently in different libraries to perform a specific action on an event. Here is the basic syntax of how to create anonymous objects in Java –
With this discussion, we come to an end of this article. I hope you must have gained the maximum knowledge of objects in Java and how to create an object using different techniques in Java. You can use any of these five techniques based on your preferences and requirements.
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