Question

(java)

1. Explain the concept of benevolent side effects. Give an example that illustrates the concept. do not use the rat/rational example

Note: You are not required to provide a comprehensive example. It is good to use one that can just illustrate the concept clear enough.

Answer 1

Benevolent side effects:

Not every side effect needs to be documented with an effects clause. If a side effect does not affect the abstract value that a mutable representation maps to, the side effect will be invisible to the user of the abstraction. Therefore, it need not be mentioned in the specification. Side effects of this sort as known as benevolent side effects, because they are not destructive. Benevolent side effects can be useful for building caches internal to data structures, or for data structure reorganizations that improve performance without affecting their abstract value.

Examples of benevolent side effects:

For Example, consider computing a hash code for an instance of a class, since this can be computationally costly, an implementation may require to compute the hash code, the first time it is asked for and then cache the result in a private feild

of the object. When the hash code is requested in subsequent occasions, the cached result is returned without further computation. For example this is done in the hashCode method of java's String class. However in JML storing the computed hashcode into the cache is considered to be a side effect. so, String's hashCode method cannot be specified as pure.