INSTRUCTIONS: =================================== You have been presented with a

Question

INSTRUCTIONS:
===================================
You have been presented with a description and purpose of the
Dependency Inversion Principle (DIP). You will need to understand this
principle to successfully complete the lab work.

DIP RULES:
A. HIGH LEVEL MODULES SHOULD NOT DEPEND UPON LOW
LEVEL MODULES. BOTH SHOULD DEPEND UPON ABSTRACTIONS.

B. ABSTRACTIONS SHOULD NOT DEPEND UPON DETAILS. DETAILS
SHOULD DEPEND UPON ABSTRACTIONS.

DIP OBJECTIVES:
1. Reduce rigidity and fragility.
2. Improve portability (code reuse, flexibility)


------------------------------------------------------------------------
In this lab you are building a program from scratch, and this process
should be thought of as a practice test, in advance of the upcoming test,
which will be very similar. To succeed follow these instructions:

Use the OOA/D goals that you memorized:

* Generic Analysis: Define the problem and its requirements:

This can be accomplished by reading the project specification below.

* Object-Oriented Analysis: Find the conceptual objects in
the problem domain:

After reading the project specification, look for, or think of nouns
that represent the objects you will need. There should be six key
nouns and these should be fairly obvious.

* Generic Design: Find a conceptual solution:

Create a Domain Model as follows...
Using pencil and paper, draw boxes containing conceptual object names,
connected by association lines, labeled to describe the association.
You should have one box for each of six key conceptual objects.

* Object-oriented Design: Skillfully Assigning Responsibilities to Objects:

Now that you have a good idea of the objects you will need and how
they will collaborate (communicate) with each other, apply the DIP and
all best practices learned so far to write code that follows your
Domain Model and skillfully assigns the right responsibilities to the
right objects. Ask yourself, what should this object do, and what
should it not do?



Criteria for Assessment: apply the DIP and all best practices learned so far
(encapsulation, Liskov Substitution, no magic numbers, validation or at
least validation comments, proper naming and capitalization, etc.).

PROJECT SPECIFICATIONS:
----------------------
We need a simple messaging system that is flexible enough to provide
messages in different ways and render those messages in different ways.

For example a message provider might be needed for error messages, or
random tip of the day messages, or welcome messages. Message rendering is the
act of outputting the provided message to various destinations: the
console or a GUI, for example. So you might need a console renderer and a
GUI renderer to start, but be able to added other message renderers (file
renderer, e.g.) in the future. Switching message providers or message
renderers should be easy and should not break code.

The actual wording of the messages is not important for this first version,
however, you will need to support at least two different ways of providing
a message and at least two different ways of rendering a message. And we want
as much code as possible to be portable and flexible so that changes don't
require much editing. For example, in the IndependentCopy sample, it was the
Copier class and Reader and Writer interfaces that were portable.

In addition to the code for managing your providers and renderers, you will
need a Startup class with a main method to start the program and do some
basic initialization. But remember, input comes from the provider components
and output goes to the renderer components. That means your program
should have at least 6 classes: one startup, one manager, two providers and
two renderers.

For those of you who don't know how to do simple input/output GUIs, here's
some sample code:

For an output GUI, just use a JOptionPane.showMessageDialog() method, but you
must remember to do an import first, above your class declaration, but below
the package reference:

package dip.lab;

import javax.swing.JOptionPane;

public class MyClass { ...

... then to use it just do this:

JOptionPane.showMessageDialog(null,"My Message");

... then to do input, if necessary, do this:

String response =
JOptionPane.showInputDialog(null, "A Prompt, like enter message here:");

For more information, see the online JavaDoc for the JOptinPane class in
Java SE 6.

Explanation / Answer

public class DataCollector { public void collectData(String source) { //collect the data from source, let us say String data //initialise a DataWriter object DataWriter writer = new DataWriter(); //ask the writer object to write the data writer.writeData(the collected data); } } public class DataWriter { public void writeData(the data) { //write the data to the database DatabaseWriter dw = new DatabaseWriter(); dw.writeToDB(params); } } public class DatabaseWriter { public void writeToDB(params) { //write physically to the database } }

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