Java Class

What is class in java?

Class is a user defined data type.

All the data/fields and methods/functions are encapsulated within the class. The data and methods written within the class are called as members of class.

When we define any class, we are not defining any data, we just define a structure or a blueprint, as to what the object of that class type will contain and what operations can be performed on that object.

Syntax

class className
{
	// instance variable declaration
	type/datatype  variable1;
	type/datatype  variable2;
	.
	.
	.
	type/datatype  variableN;

	//	method declaration
	return_type method_name( parameter list..)
	{
		// body of method
	}
}

Explanation

Instance variable declaration

they are called as instance variables because they are created whenever an object of the class is instantiated. These are accessible to all the functions written inside the class.

Method declaration

Method means functions. Methods are used for working on the data contained in the class.

Example of class

Consider the Class of Cars. There may be many cars with different names and brand but all of them will share some common properties like all of them will have 4 wheels, Speed Limit, Mileage etc. So here, Car is the class and wheels, speed limits, mileage are their properties.

class Cars
{
     static byte wheels;
     static int speed_limit, mileage; 

     static void apply_break()
     {
	 System.out.println("Break pressed");
     }
     static void increase_speed()
     {
	 System.out.println("Speed increased");
     }
     public static void main(String args[])
     {
       wheels = 4;
	 speed_limit = 120;
	 mileage = 23;
	 System.out.println("wheels  : "+wheels+" speed limit : " +speed_limit+" mileage : "+mileage);
	 apply_break();	// calling member function
	 increase_speed();
     }
}
	

Output

In the above example of class Cars, the data member will be speed limit, mileage etc. and member functions can be applying brakes, increase speed etc.

Why static fields and methods?

In java, the main method accepts only static type of data and methods from outside the main method. that’s why we have not to worry about creating an object of same class for calling the methods or initializing the fields.

We will Learn more about static keyword on later tutorial.