Bad or broken designs

Quite often, the structure or design and patterns used in implementing an application can result in bad code, most especially when object-oriented programming principles or design patterns are wrongly used. A common anti-pattern is spaghetti coding. It is common among developers with little grasp of object-orientation and this involves creating a code base with unclear structures, little or no reusability, and no relationships between objects and components. This leads to applications that are difficult to maintain and extend.

There is a common practice among inexperienced developers, which is the unnecessary or inappropriate use of design patterns in solving application complexity. The design patterns when used incorrectly can give a code base bad structure and design. The use of design patterns should simplify complexity and create readable and maintainable solutions to software problems. When a pattern is causing a readability issue and overtly adding complexity to a program, it is worth reconsidering whether to use the pattern at all, as the pattern is being misused.

For example, a singleton pattern is used to create a single instance to a resource. The design of a singleton class should have a private constructor with no arguments, a static variable with reference to the single instance of the resource, and a managed public means of referencing the static variable. A singleton pattern can simplify the access to a single-shared resource but can also cause a lot of problems when not implemented with thread safety in mind. Two or more threads can access the if (smtpGateway==null) line at the same time, which can create multiple instances of the resource if the line is evaluated to true, as with the implementation shown in the following code:

public class SMTPGateway
{
    private static SMTPGateway smtpGateway=null;

    private SMTPGateway()
    {
    }

    public static SMTPGateway SMTPGatewayObject
    {
        get
        {
            if (smtpGateway==null)
            {
                smtpGateway = new SMTPGateway();
            }
            return smtpGateway;
        }
    }
}