Java – Class and Objects with Example3 min read

Java is an Object-Oriented Language. And classes and objects are the fundamental components of OOP’s.

Objects are real-life entity and classes are the blueprint for creating an object. For example: consider a class for a car, it has color, some weight, size, etc, these are its attributes and drive, gear, brake, etc are its behaviour.

CLASS

A class is a user-defined blueprint or prototype for creating Objects. It is a logical entity. We can say that classes are categories, and objects are items within each of those categories.

A class in Java contain:

  • Methods.
  • Fields.
  • Constructors.
  • Interfaces.

For the declaration of a class following components are included:

1. Modifiers:
A class can be public or default access.

2. Class name:
A class should have a name with an initial letter Capitalized.

3. SuperClass(if any)/ Interfaces:
If required to include SuperClass then proceed by the keyword ‘extends’. Using the keyword implements, a class can have more than one interface.

4. Body:
A class boundary is within the curly braces'{}’.

Syntax for class:

Syntax example:


OBJECTS:

It can be defined as real-world entities that have state and behavior. An object is a runtime entity. Eg. bike, Lamp, pen, table, etc. An Object is an instance of a class. It is a physical as well as a logical entity.

Objects has three characteristics:

  • State: It is represented by attributes of an object that is the data value.
  • Behaviour: It represents the functionality that is the behaviour of an object. Example withdraw, deposit, etc.
  • Identity: It is a unique ID given to each Object created so that JVM can identify all the objects uniquely.

Example:
Name of an Object: dog
Identity: Name of the dog.
State: age, color, breed, size, etc.
Behaviour: eat, sleep, bark, run, etc.

Creating an Object:

As mentioned above that class is a blueprint for objects. So, Object is created from a class. And ‘new’ Keyword is used to create an Object.Three steps to create Object:

  • Declaration: Declaration of a variable with the variable name with an object type.
  • Instantiation: When an object of a class is created, it is said to be instantiated. And the ‘new‘ keyword is used to create an object.
  • Initialization: The ‘new’ operator allocates memory for a new object that is being instantiated. Also invokes the class constructor.

Syntax of Object:


Following Example shows the creation of an Object:

Output:


Creating Multiple Objects:

Multiple Objects can be created for the same class.

The following example shows that Objects are created for One class, invoking different variables.

Output:


Example of class and objects in Java:

Output:


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