Object and Class in Java

1) Object

Object is real life entities that has state, behavior and identity is known as an object.
For example, a chair, pen, table, keyboard, bike, etc. every thing is an object

State : It is represented by attributes of an object. It also reflects the properties of an object.
Behavior : It is represented by methods of an object. It also reflects the response of an object with other objects.
Identity : It gives a unique name to an object and enables one object to interact with other object

Example : Dog

2) Class

Class is blue print of an object that means It represents the set of properties or methods.

class can contain that is:

Fields
Methods
Constructors
Blocks
Nested class and interface

Syntax of class declare :

class <class_name>{
   field;  
  method;
}

What is Method in Java .?

Method is like a function which is used to pass data, as a parameters, into a method, expose the behavior of an object.

Advantage of Method

Code Reusability
Code Optimization

Example :

 public class Pradeep {
  static void myMethod() {
    System.out.println("My Name is Rajvanshi!");
  }

  public static void main(String[] args) {
    myMethod();
  
  }
}

Output

new keyword in Java

→ Objects are created by the help of "new" keyword. new keyword is used to allocate memory at runtime

→ new keyword is used to create a new object of a class.

Example : Create a new instance of a class:

  class Car {
   }
Car newCar = new Car();

Full Example1 :

 public class Car
 {
  int price = 500000;
  public static void main(String args[])
  {
    Car rate = new Car();
    System.out.println("Car Price is Rs."+rate.price);
  }
 }

Output

Example2 :

 public class Car
{
  String newcar = "Ford";
  public static void main(String args[])
  {
    Car c = new Car();
    System.out.println("My Car name is ."+c.newcar);
  }
}

Output

Initialize object

There are 3 ways to initialize object in Java.

By reference variable
By method
By constructor

1) Initialization Reference variable

initialize the object through a reference variable.

Example1 :

   class Student{  
    int id;  
   String name;  
 }  
class TestEx{  
 public static void main(String args[]){  
     //Creating objects  
  Student s1=new Student();  
  Student s2=new Student();  
  //Initializing objects  
  s1.id=01;  
  s1.name="Pradeep";  
  s2.id=02;  
  s2.name="Jon";  
   //Printing data  
  System.out.println(s1.id+" "+s1.name);  
  System.out.println(s2.id+" "+s2.name);  
 }  
}  

Output : (1)save by the class Student.java name and run TestEx see in fig..

Output : (2) Direct save by the class TestEx.java name and run TestEx see in fig..

2) Initialization through method

We are creating the objects of Student class and initializing the value to these objects by invoking the insertRecord method. Here, we are displaying the data of the objects by invoking the display() method.

Example1 :

   class Student{  
  int id;  
 String name;  
 void insertRecord(int i, String n){  
  id =i;  
  name=n;  
 }  
 void display()
  { 
   System.out.println(id +" "+name);}  
  }  
  class TestStudent{  
  public static void main(String args[]){  
   Student s1=new Student();  
   s1.insertRecord(01,"Peeter");  
   s1.display();  
 }  
}

Output

Initialization through method Example in Java

3) Initialization through a constructor

Next Topic discuss, More Details....

Create an object in Java?

There are three ways to create an object in java. That is....

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

Anonymous object

Anonymous 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 you can use :

Calling method through a reference:

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

Calling method through an anonymous object

Example

  class FactorialEx
   {
 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 FactorialEx().fact(5);//calling method with anonymous object
}
}

Output:

Next TopicConstructor

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OOPs Concepts

Object and Class in Java

1) Object

2) Class

class can contain that is:

Syntax of class declare :

What is Method in Java .?

Advantage of Method

Example :

new keyword in Java

Example : Create a new instance of a class:

Full Example1 :

Example2 :

Initialize object

1) Initialization Reference variable

Example1 :

2) Initialization through method

Example1 :

3) Initialization through a constructor

Create an object in Java?

Anonymous object