Authentication is any process by which you verify that someone is who they claim they are. This usually involves a username and a password, but can include any other method of demonstrating identity, such as a smart card, retina scan, voice recognition, or fingerprints. Authentication is equivalent to showing your drivers license at the ticket counter at the airport.

Authorization is finding out if the person, once identified, is permitted to have the resource. This is usually determined by finding out if that person is a part of a particular group, if that person has paid admission, or has a particular level of security clearance. Authorization is equivalent to checking the guest list at an exclusive party, or checking for your ticket when you go to the opera.

Finally, access control is a much more general way of talking about controlling access to a web resource. Access can be granted or denied based on a wide variety of criteria, such as the network address of the client, the time of day, the phase of the moon, or the browser which the visitor is using. Access control is analogous to locking the gate at closing time, or only letting people onto the ride who are more than 48 inches tall - it's controlling entrance by some arbitrary condition which may or may not have anything to do with the attributes of the particular visitor.

Because these three techniques are so closely related in most real applications, it is difficult to talk about them separate from one another. In particular, authentication and authorization are, in most actual implementations, inextricable.

1.Introduction to Object-Oriented Programming
Object-Oriented programming(OOP) is the dominant programming paradigm these days.
Java is totally object-oriented.
You don’t care how the functionality was implemented. In OOP, you only care about what the object expose.
The Vocabulary of OOP
A class is a template or blueprint from which objects are actually made.
Encapsulation(date hiding) is a key concept in working with objects. Formally, encapsulation is nothing more than combining data and behavior in one package and hiding the implementation of the data from the user of the object.
When you extend an existing class, the new class has all the properties and methods of the class that you extend.
Objects
The three key characteristics are:
 The object’s behavior – what can you do with this object, or what methods can you apply to it.
 The object’s state – how does the object react when you apply those methods?
 The object’s identity – how is the object distinguished from others that may have the same behavior and state?
Relationship Between Classes
 Dependence(“uses-a”)
 Aggregation(“has-a”)
 Inheritance(“is-a”)

2.Using Existing Classes
Objects and Object Variable
In the Java programming language, you use constructors to construct new instance. A constructor is a special method whose purpose is to construct and initialize objects.
Constructors always have the same name as the class name.
An object variable doesn’e actually contain an object. It only refers to an object.
You should think of Java object varialbes as analogous to object pointers in C++:
Date birthday; //Java
is really the same as
Date* birthday; //C++
All Java objects live on the heap. When an object contains another object variable, that variable still contains just a pointer to get another heap object.
Mutator and Accessor Methods
Methods that change instance fields are called mutator methods and those only access instance field without modifying them are called accessor methods.

translation of words:
dominant – stronger, more powerful, or more noticeable than other people or things.
paradigm – a very clear or typical example of something
expose - show
combine – mix, join together