Java Classes and Objects

Java Class

In Java everything is encapsulated under classes. Class is the core of Java language. It can be defined as a template that describe the behaviors and states of a particular entity.

In Java, class is declare using class keyword. A class contain both data member and methods that operate on that data. The data or variables defined within a class are called instance variables and the code that operates on this data is known as methods.

Thus, the instance variables and methods are known as class members.

Create a class in Java

We can create a class in Java using the class keyword.

Syntax:

class ClassName {
    // dataMember
    // methods
}

Example:

class Simple {
    // dataMember
    int number = 3;

    // method
    void message()
    {
        System.out.println("Hi i'm method in a class Simple")
    }
}

In the above example, we have created a class named Simple. It contains a dataMember number and a method named message().

Java Objects

Object is an instance of a class. An object in OOPS is nothing but a self-contained component which consists of methods and properties to make a particular type of data useful. When you send a message to an object, you are asking the object to invoke or execute one of its methods as defined in the class.

In a simple word object is a real world entity which have predefined attributes and its beheviour. It has a physical thing as well as abstract in nature.

Creating an Object in Java

Here is how we can create an object of a class.

Syntax:

ClassName ReferenceVariable = new ClassName();

Example:

class Simple {
    int x = 10;

    public static void main(String[] args) {
        Simple obj = new Simple();
        System.out.println(obj.x);
    }
}

Output:

10

Multiple Objects

We can also create multiple objects of one class. Here is the example of multiple object creation.

class Simple {
    int x = 10;
    int y = 20;

    public static void main(String[] args) {
        Simple obj1 = new Simple();
        Simple obj2 = new Simple();
        System.out.println(obj1.x);
        System.out.println(obj2.y);
    }
}

Output:

10

20