Java.lang.Object

Java.lang.Object Class:

• For all classes java.lang.Object is a base class.
• The important methods of java.lang.Object class is:
• toString();
• hashCode();
• equals();
• getClass();
• Notify();
• NotifyAll();
• Wait();

Note: The methods marked in blue color can override, and the methods marked in red color cannot be override.

Difference between Primitive types and Objects

Primitive Types:

• Primitives types are loaded in stack.
• When the primitive is assigned to another primitive type copy is created.
• Primitive types are not polymorphic, so it cannot be passed as to a method that takes object as a parameter.

Objects:

• Objects are loaded in heap
• When object reference is assigned to another object reference,they share the same object
• Objects are Polymorphic, so they can be passed as a parameter to any method that takes object as parameter.

OOPS Concepts

• Encapsulation
• Inheritance
• Polymorphism
• Abstraction

Encapsulation:

• Encapsulation is the mechanism that binds together code and the data it manipulates and keeps both safe from outside interference and misuse.

Inheritance:

• Inheritance is the process by which one object acquire the properties of another object.

Polymorphism:

• Polymorphism provides a way to take more than one form.
• Two types of Polymorphism.                        

                               1. Compile Time Polymorphism (Overloading)

                               2. Run Time Polymorphism (Overriding)
Abstraction:

• Abstraction allows user to view only the essential features without knowing the background details.
• In other sense we can say that, it deals with the outside view of an object (interface).

Object

• Object is an instance of a class.
• Using Object we can access non static member variables and member methods.
• If we use Objects for accessing static members, a same memory is shared for all Objects.
• So use class name for accessing static members instead of Objects.

Class

• Class is a user defined data type.
• Class contains member variables and member methods.
• Using Class we can create any number of objects.

Benefits of Java

• Java is Object Oriented language.
• Java is platform independent.
• Java code is reusable and change friendly.
• Java application don't have memory leak.
• Java applications are easy to install.