This paper presents a kind of software design measures that help us to determine the application of Gang-Of-Four design patterns to refactoring processes. Refactoring using design patterns is one of the promising approaches to improve the designs during development activities, and a crucial issue is to identify when, where and which patterns could be applied. We analyzed several actual object-oriented designs of low quality needed to be refactored and focus on the characteristics of conditional statements of methods and inheritance structures, which seemed to cause the low quality. We provide 20 measures to objectively detect these characteristics in object-oriented designs. These measures express the complexity of branching execution in conditional statements and the strength of the dependency among the sub classes in the inheritance trees. Designers can be guided to recognize when, where and which design patterns should be used, in order to refactor their designs of low quality, by calculating these measures. We apply our approach to the low-quality design of the drawing editor that was produced by a novice designer and assess the effectiveness of our measures.
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