Showing posts from February, 2016

Exception Handling: File CRUD Operations Example

Introduction to Exception Handling This is a supplement to my previous blog Creating Custom Exception Classes in Java . I recommend you read that one first and then read this one. Java provides many Exception (and Error) Handling classes. Both of these categories implement the Throwable interface. Although it is not imperative that you develop your own custom exception classes, it is often a good idea to do so; particularly when dealing with large systems. The main reason to create custom exception classes is to quickly identify which custom class is being affected or causing these custom exceptions. For example, referencing a null object and trying to use it will result in a NullPointerException . However, in your code, there could be literally hundreds or even thousands of statements which could result in such exception. Designing your Custom Exception Class Suppose that you are designing a class that will serve as a message receiver. For simplicity,

Creating Custom Exception Classes in Java

Introduction My first piece of advice: Search the web. There is a ton of information that is available to you on the Internet. However, beware where you go for information. There are many places with bad information as well. For this topic, the safest source of information is the Oracle The Java Exceptions Tutorials . Starting with the basics, the first thing to do is determine whether or not you need the custom exception class to begin with. We are going to assume we need to handle an exception that it is not clearly represented already in Java. To create a custom exception class, we must use a name that it is meaningful. Typically, the exception class is named after a process or a class name that will throw the exception. For instance, if I create a MessageReceiver class that could result in an exception, I might consider naming my exception class MessageReceiverException. The UML diagram below depicts this relationship between the class and the custom

How to create Javadoc comments

This document is a summary of the information found on the Oracle website: My goal is to give you a summarized version of the following topics: ·          What is Javadoc and why is it needed? ·          How to document your code using Javadoc ·          How to generate Javadoc documentation ·          How to publish Javadoc What is Javadoc and why is it needed? In simple terms, Javadoc is a tool for documenting your code in HTML format. Because this documentation is in HTML, it can be easily uploaded to a web server and made available online for the whole world to see. An example of this is the Java API ( ). For many developers, one of the selling points of Java over other languages like C++ was in fact Javadoc. Why? If you consider one of the most common libraries in C++, stdio, most of the documentation found online is

Aggregation and Composition

When determining the relationship between object at design time, it is easy to succumb to the habit of using inheritance; simply because it is easy.  In a language such as C++, it is even easier to do so because the language supports multiple inheritance. Figure  1 : the java.util. List  Interface Assume that Java does not have a Stack (java.util.Stack) class and you need to create a custom stack (call it MyStack).  You could do this in three different ways, but for the purposes of this paper I will discard the creation of the Stack class as shown in the image above.  Therefore, assume that there are only two ways.  The first way is to extend the ArrayList class.  The second way is to include an ArrayList object as a data member.  The first solution uses inheritance to solve the problem.  Remember, inheritance establishes an “is-a” relationship between objects.  Therefore, the relationship between MyStack and ArrayList is incorrect since a stack is not

Specialization, Generalization, and Abstraction

A question was raised on LinkedIn (you can follow me there: ) that got me thinking and I decided to blog about it. I am going to start by defining what generalization means in Object-Oriented Programming (OOP) and Design (OOD). Generalization in OOD implies that a specialized (child) class is based on a general (parent) class. This, in turn, implies a "is-a" relationship. When you analyze the object types and their relationships as depicted in the image above, from left to right, it goes from very general to more specific. You could say that an Animal "is a" more general form of Dog, of Canine, and even than Mammal. Likewise, a Canine "is a" more general form of Dog. If you analyze it from right to left, the opposite happens: it goes from more specific to more general. Put in other terms, the type gets broadened. Therefore, you can still refer to dogs as canines, mammals, or even animals.