Designing Robust Constructors (and Perhaps Destructors)

When designing a class, one of the most important design issues involves how the class will be constructed. Constructors are discussed in Chapter 3, “Advanced Object-Oriented Concepts.” Revisit this discussion if you need a refresher on guidelines for designing constructors.

First and foremost, a constructor should put an object into an initial, safe state. This includes issues such as attribute initialization and memory management. You also need to make sure the object is constructed properly in the default condition. It is normally a good idea to provide a constructor to handle this default situation.

In languages that include destructors, it is of vital importance that the destructors include proper clean-up functions. In most cases, this clean-up pertains to releasing system memory that the object acquired at some point. Java and .NET reclaim memory automatically via a garbage collection mechanism. In languages such as C++, the developer must include code in the destructor to properly free up the memory that the object acquired during its existence. If this function is ignored, a memory leak will result.