Object in Java

An object has three characteristics:

State: represents the data (value) of an object.
Behavior: represents the behavior (functionality) of an object such as deposit, withdraw, etc.
Identity: An object identity is typically implemented via a unique ID. The value of the ID is not visible to the external user. However, it is used internally by the JVM to identify each object uniquely.

An object is an instance of a class. A class is a template or blueprint from which objects are created. So, an object is the instance(result) of a class.

Object Definitions:

An object is a real-world entity.
An object is a runtime entity.
The object is an entity which has state and behavior.
The object is an instance of a class.

There are 3 ways to initialize object in Java.

By reference variable
By method
By constructor

Initialization through reference class Student{
int id;
String name;
}
class TestStudent2{
public static void main(String args[]){
Student s1=new Student();
s1.id=101;
s1.name="Sonoo";
System.out.println(s1.id+" "+s1.name);//printing members with a white space
}
}

Initialization through method class Student{
int rollno;
String name;
void insertRecord(int r, String n){
rollno=r;
name=n;
}
void displayInformation(){System.out.println(rollno+" "+name);}
}
class TestStudent4{
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();
}
}

Initialization through a constructor class Employee{
int id;
String name;
float salary;
void insert(int i, String n, float s) {
id=i;
name=n;
salary=s;
}
void display(){System.out.println(id+" "+name+" "+salary);}
}
public class TestEmployee {
public static void main(String[] args) {
Employee e1=new Employee();
Employee e2=new Employee();
Employee e3=new Employee();
e1.insert(101,"ajeet",45000);
e2.insert(102,"irfan",25000);
e3.insert(103,"nakul",55000);
e1.display();
e2.display();
e3.display();
}
}

There are many ways to create an object in java. They are:

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

Anonymous object

Anonymous simply means nameless. An object which has no reference is known as an anonymous object. It can be used at the time of object creation only.

If you have to use an object only once, an anonymous object is a good approach. For example:

new Calculation();//anonymous object  

Calling method through a reference:

Calculation c=new Calculation();  
c.fact(5);  

Calling method through an anonymous object

new Calculation().fact(5);  

Let's see the full example of an anonymous object in Java.

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 anonymous object  
}  
}