Naming convention

Naming convention

A naming convention is a rule to follow as you decide what to name your identifiers (e.g. class, package, variable, method, etc.), but it is not mandatory to follow that is why it is known as convention not rule.
 
Advantage:

By using standard Java naming conventions they make their code easier to read for themselves and for other
programmers. Readability of Java code is important because it means less time is spent trying to figure out
what the code does.

class name : should begin with uppercase letter and be a noun e.g.String,System,Thread etc.
 
Interface name : should begin with uppercase letter and be an adjective (whereever possible). e.g.Runnable,ActionListener etc.
 
method name : should begin with lowercase letter and be a verb. e.g.main(),print(),println(),actionPerformed() etc.
 
variable name : should begin with lowercase letter e.g. firstName,orderNumber etc.
 
package name : should be in lowercase letter. e.g. java,lang,sql,util etc.
 
constants name : should be in uppercase letter. e.g. RED,YELLOW,MAX_PRIORITY etc.


Object and Class (Object-Oriented Programming)
In this page, we will learn about the objects and classes.In object-oriented programming, we design a program using objects and classes. Object is the physical entity whereas class is the logical entity. A class works as a template from which we create the objects.
 
Object

A real world entity that have state and behaviour is known as an object. For example: chair, table, pen etc.
An object have three characterstics:

• state:represents the data of an object.
• behaviour:represents the behaviour of an object.
• identity:Object identity is typically implemented via a unique ID. The value of the ID is not visible to the external user, but is used internally by the JVM to identify each object uniquely.

For Example: Pen is an object. Its name is Reynolds, color is white etc. known as its state. It is used to write, so writing is its behaviour.
Object is an instance of a class.Class is a template or blueprint from which objects are created.So object is
the instance(result) of a class.

Class 

A class is a group of objects that have common property. It is a template or blueprint from which objects are
created.
A class in java can contain:

• data member
• method
• constructor
• block

Syntax of class: 

class <class_name>{
data member;
method;
}

Simple Example of Object and ClassIn this example, we have created a Student class that have two data members id and name. We are creating
the object of the Student class by new keyword and printing the objects value.
 

class Student{
int id;//data member (also instance variable)
String name;//data member(also instance variable)
public static void main(String args[]){
Student s1=new Student();//creating an object of Student
System.out.println(s1.id+" "+s1.name);

}
}
Output:0 null

Instance variableA variable that is created inside the class but outside the method, is known as instance variable.Instance
variable doesn't get memory at compile time.It gets memory at runtime when object(instance) is created.That
is why, it is known as instance variable.
 

MethodIn java, a method is like function i.e. used to expose behaviour of an object.
 

Advantage of Method

• Code Reusability
• Code Optimization

new keywordThe new keyword is used to allocate memory at runtime.

Example of Object and class that maintains the records of studentsIn this example, we are creating the two objects of Student class and initializing the value to these objects by
invoking the insertRecord method on it. Here, we are displaying the state (data) of the objects by invoking the displayInformation method.

class Student{
int rollno;
String name;
void insertRecord(int r, String n){ //method
rollno=r;
name=n;
}
void displayInformation(){System.out.println(rollno+" "+name);}//method
public static void main(String args[]){
Student s1=new Student();
Student s2=new Student();
s1.insertRecord(111,"Karan");
s2.insertRecord(222,"Aryan");
s1.displayInformation();
s2.displayInformation();
}
}
Output:111 Karan
222 Aryan

 

As you see in the above figure, object gets the memory in Heap area and reference variable refers to the
object allocated in the Heap memory area. Here, s1 and s2 both are reference variables that refer to the
objects allocated in memory.

Another Example of Object and Class
 

There is given another example that maintains the records of Rectangle class. Its exaplanation is same as in
the above Student class example.

class Rectangle{
int length;
int width;
void insert(int l,int w){
length=l;
width=w;
}
void calculateArea(){System.out.println(length*width);}
public static void main(String args[]){
Rectangle r1=new Rectangle();
Rectangle r2=new Rectangle();
r1.insert(11,5);
r2.insert(3,15);
r1.calculateArea();
r2.calculateArea();
}
}
Output:55
45

What are the different ways to create an object in Java?There are many ways to create an object in java. They are:

• By new keyword
• By newInstance() method
• By clone() method
• By factory method etc.

We will learn, these ways to create the object later.

Annonymous object
Annonymous simply means nameless.An object that have no reference is known as annonymous object.

If you have to use an object only once, annonymous object is a good approach.
class Calculation{
void fact(int n){
int fact=1;
for(int i=1;i<=n;i++){
fact=fact*i;
}
System.out.println("factorial is "+fact);
}
public static void main(String args[]){
new Calculation().fact(5);//calling method with annonymous object
}
}
Output:55
45
Creating multiple objects by one type only:We can create multiple objects by one type only as we do in case of primitives.
 

Rectangle r1=new Rectangle(),r2=new Rectangle();//creating two objects
 

Let's see the example:
 

class Rectangle{
int length;
int width;
void insert(int l,int w){
length=l;
width=w;
}
void calculateArea(){System.out.println(length*width);}
public static void main(String args[]){
Rectangle r1=new Rectangle(),r2=new Rectangle();//creating two objects
r1.insert(11,5);
r2.insert(3,15);
r1.calculateArea();
r2.calculateArea();
}
}
 

Output:55
45