Java Object and Classes Tutorial

What is an Object in Java

An object is an entity that has a state and behavior.

• State: Represents 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. But, it is used internally by the JVM to identify each object uniquely.

Real World Example:

A pen is an object that has state (color, name, etc.) and behavior (writing).

A car is an object that has state (color, brand, etc.) and behavior (accelerating, braking).

What is a Class in Java

A class is a group of objects which have common properties. It is a template or blueprint from which objects are created. It contains:

• Fields
• Methods
• Constructors
• Blocks
• Nested class and interface

Syntax to declare a class:

class ClassName {
    //fields
    //methods
}

Java Object and Class Example

In this example, we have created a Student class that has 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 = 1;  
    String name = "John";  
}  

class TestStudent {  
    public static void main(String args[]) {  
        Student s1 = new Student();  
        System.out.println(s1.id);  
        System.out.println(s1.name);  
    }  
}