Understanding Object Oriented Programming

1.....In OOP we create and use objects. 
2.....Each object is an instance (created entity ) of a specific class.
3.....Many classes already exist and many more are being developed each day.
4.....Each class has characteristics and capabilities.
5.....Characteristics can be viewed as the physical features that all objects of the class will take on.
6.....Capabilities can be viewed as actions that all objects of the class will be capable of doing.
7.....Since hundreds of these classes already exist, programmers do not need to reinvent the wheel
       every time they want to write a program.
8.....Programmers still use the primitive data types and the standard logic and control structures of
       a specific language but now they have access to a big collection of items (classes) that a already do
       things for them.
9.....The key is is learn how to incorporate these new classes into a program to facilitate the overall
       programming task.
10...The following general guidelines are not  all encompassing by any means but they can be viewed as
       a very good starting point.
11...Create an object of an existing class or of a class of your own creation. --  using the "new" keyword
12...This means that the physical feature (instance variables) have been created and you are ready
       to give them values and use the capabilities (methods) that have already been provided for that class.
13...Using a method on an object of a class is normally pretty simple  >>   object_name.method
14...I t now gets a little more complicated because in order use use objects and methods properly
       and in more sophisticated applications, a programmer needs to thoroughly understand about parameters
       and returned values.
15...The above is critical because many aspects of object oriented programming involve
       "objects communicating with each other"
16...Objects basically send and receive messages (values, references etc.) back and forth.
      EXAMPLE       String name = person.substring(1,20);
17...In the above, the substring method is called on the person object and it is passed 2 parameters. These
       parameters are needed by the method.
18...The method in the above is a NON void method because it RETURNS a String value. And in this example
        the value is assigned to another String object.called name.
19....This concept of objects communicating by passing values back and forth is critical to understanding OOP..
20....You can create your own classes and provide methods that allow the outside world to have access to
         your instance variables or use existing classes and their methods. Either way, you create objects of the
         respective class and you can use their methods on your new object. You also have the right to override
         methods not quite suited to your specific task. Bottom line is "you must know how to use the methods
         and handle what they give you back -- NO SURPRISES".