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Summary A design pattern is a general reusable solution to commonly recurring problems in software projects. Bad smells are symptoms existing in the source code that possibly indicate the presence of a structural problem that requires code refactoring. Although design pattern and bad smells be different concepts, literature has shown that they may be related and cooccur during the evolution of a software system. This paper presents an empirical study that investigates cooccurrences of design patterns and bad smells as well as identifies the main factors that contribute to the emergence of the relationship between them. We carried out a case study with five Java systems to: (1) investigate if the use of design pattern reduces bad smell occurrence, (2) identify cooccurrences of design patterns and bad smells, and (3) identify situations that contribute for the cooccurrence emergence. As the main result, we found that the application of design pattern not necessarily avoid bad smell occurrences. The results also show that some design patterns such as composite, factory method, and singleton, are intrinsically modular and might be useful in creating high‐quality systems. However, other design patterns such as adapter‐command, proxy, and state‐strategy, have presented high cooccurrence frequency with bad smells; therefore, they require attention in their implementation. Finally, via manual inspection in the components with cooccurrence, we found that the identified cooccurrences appeared due to poor planning and inadequate application of design patterns.

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Design patterns are general reusable solutions to common recurring problems in software projects. These solutions, when correctly applied, are supposed to enhance modular and flexible structures in software. The aim of this work is to study the occurrences of God Class and Long Method bad smells in software systems developed with design patterns. To achieve this aim, we carried out a study with five Java project, in order to: (i) investigate if the use of GOF design patterns avoid the occurrences of the bad smells God Class and Long Method, (ii) identify co-occurrences of the GOF design patterns with these bad smells, and (iii) identify the main situations that lead software systems to present these co-occurrences. The results obtained suggest that Composite and Factory Method have a low co-occurrence with these bad smells, and Template Method and Observer have a high co-occurrence with God Class and Long Method, respectively. In addition, we have identified that the misuse of design patterns and the scattering and crosscutting concerns has contributed to the emergence of such co-occurrences.

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