Objects and Classes in Java

What is an object in Java

• A member (also known as an instance) of a Java class is a Java object. Every object has a state, a behaviour, and an identity.
• In Java, the word "new" is used to create an object.
• The items we can see in the actual world and Java objects are extremely similar. An item can be a pet, a lighter, a pen, or an automobile.
• Object has 3 characteristics:
• State:: State represents an object's data (value).
• Behavior : Behavior reflects how a thing behaves (or how it functions), such as when you deposit or withdraw money from your bank account. its own.
• Identity :Usually, a distinct ID is used to implement an object's identification. The external user cannot see the value of the ID. However, the JVM uses it internally to uniquely identify each object its own.
• For Example, Car is an object. Its name is Nano; color is red, known as its state. It is used to drive, so drive is its behavior.

Java objects' properties

• A thing in the actual world is an object
• An entity at runtime is an object.
• An entity with state and behaviour is an object.
• The object is a class instance.

• Usually, an object's methods may be used to communicate with it. The objects continue to have control over how the world may utilise them through states and methods.
• Individual objects of code may be created, and each object's source code can be developed and maintained separately from the others. It is simple to remove and replace any item that interferes with a program's functionality.



Syntax

The following syntax is used to create a new object of type "Student":

Student StudentObject= New Tree = Student().

Object structure

 // Java  program using class and object   

class Student2{  
	String Stu_name ;   
	int Stu_id;   
} 
class Student{  
	public static void main(String args[]){  
          Student2 studentObject=new Student2();  
          
          studentObject.Stu_id=40139522;  
          
          studentObject.Stu_name="Dr Alok Raja";  
          
    	  System.out.println(studentObject.Stu_name+" \n"+studentObject.Stu_id);
	 } 
} 

Dr Alok Raja  

40139522 

Different ways to create an object in Java

• By new keyword
• By newInstance() method
• By deserialization
• By clone() method
• By factory method

We will learn how to make these objects later.

There are 3 ways to initialize object in Java.

• Using reference variable
• Using constructor
• Using method

1.Object initialized through reference variable

 // Java  program using class and object   

class Student2{  
	String Stu_name ;   
	int Stu_id;   
} 
class Student{  
	public static void main(String args[]){  
          Student2 studentObject=new Student2();  
          
          studentObject.Stu_id=40139522;  
          
          studentObject.Stu_name="Dr Alok Raja";  
          
    	  System.out.println(studentObject.Stu_name+" \n"+studentObject.Stu_id);
	 } 
} 

Dr Alok Raja  

40139522 

2.Object initialized Using constructor

 // Java  program using class and object   

class Student2{  
	String Stu_name ;   
	int Stu_id;
	public Student2(String stu_name, int stu_id) {
		Stu_name = stu_name;
		Stu_id = stu_id;
	}   
} 
class Student{  
	public static void main(String args[]){  
		  Student2 studentObject=new Student2("Dr Alok Raja", 40139522);  
		  System.out.println(studentObject.Stu_name+" \n"+studentObject.Stu_id);
	 } 
}  
 

Dr Alok Raja  

40139522 

3.Object initialized Using Method

 // Java  program using class and object   

class Student2{  
	String Stu_name ;   
	int Stu_id;
	 void insert(String stu_name, int stu_id) {
		Stu_name = stu_name;
		Stu_id = stu_id;
	}  
	public void Display() {
		System.out.println(Stu_id);
		System.out.println(Stu_name+"\n");
	}
} 
class Student{  
	public static void main(String args[]){  
		  Student2 studentObject1=new Student2();
		  Student2 studentObject2=new Student2();
		  studentObject1.insert("Dr Alok Raja ", 40139522);
		  studentObject1.Display();
		  studentObject2.insert("Mrs Anita Sinha", 40139522);
		  studentObject2.Display();
	 } 
}  

40139522  

Dr Alok Raja 

40139532 

Mrs Anita Sinha 

What is Class in Java

• In object-oriented programming (OOPs), Classes serves as a tailored blueprint, a precise model used for creating object A class is essentially a blueprint or template that defines the properties and behaviors of objects. OOP classes lassencapsulates both data (in the form of variables) and methods that operate on that data.
• The class can be compared to a rough draught (prototype) of a home. It includes all of the information on the floors, doors, windows, etc. We construct the house in accordance with these descriptions. The item is a house.
• We may produce several objects from a class since numerous houses can be constructed using the same description.
• In Java, a class can include:
• Fields:
• Methods
• Constructors
• Blocks
• interface
• Nested class

Class structure

• Here, fields (variables) represent the state of object and methods represent the behavior of object
• fields are used to store data
• Methods are used to perform some operations

 // Java  program using class and object   

class Car {	   
    public int gear = 2; // state 
  
    public void braking()  // behavior 
    {
      System.out.println("Car braks Working");
    }
}
  





• In the preceding example, we defined a class called Car. It has a gear field and a braking method (). Car is a prototype in this context. We can now use the prototype to build an unlimited number of Car. Furthermore, all of the Car will use the prototype's fields and methods.