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Cyclomatic Complexity

Cyclomatic Complexity. Dan Fleck Fall 2009. What is it?. A software metric used to measure the complexity of software Developed by Thomas McCabe Described (informally) as the number of simple decision points + 1. What is it?.

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Cyclomatic Complexity

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  1. Cyclomatic Complexity Dan Fleck Fall 2009 Coming up: What is it?

  2. What is it? • A software metric used to measure the complexity of software • Developed by Thomas McCabe • Described (informally) as the number of simple decision points + 1 Coming up: What is it?

  3. What is it? • Essentially the number of linearly independent paths through the code • The code has no decision statements: complexity = 1 • The code has an if statement, there are two paths through the code: complexity = 2

  4. Cyclomatic Complexity V(G) Computing the cyclomatic complexity: number of simple decisions + 1 In this case, V(G) = 4 From Pressman Slides - Software Engineering a Practical Approach 6,e Coming up: What is it?

  5. Cyclomatic Complexity V(G) Convert To This is NOT a simple decision! These are simple decisions! A simple decision chooses one of two options

  6. Steps to calculate complexity • Draw the control flow graph of the code • Count the number of edges = E • Count the number of nodes = N • Count the number of connected components = P • Complexity = M – N + 2P • What is the complexity for the graph?

  7. Graph Complexity (Cyclomatic Complexity) A number of industry studies have indicated that the higher V(G), the higher the probability or errors. modules V(G) modules in this range are more error prone From Pressman Slides - Software Engineering a Practical Approach 6,e Coming up: What is it?

  8. 1 2 3 4 5 6 7 8 Basis Path Testing Next, we derive the independent paths: Since V(G) = 4, there are four paths Path 1: 1,2,3,6,7,8 Path 2: 1,2,3,5,7,8 Path 3: 1,2,4,7,8 Path 4: 1,2,4,7,2,4,...7,8 Finally, we derive test cases to exercise these paths. From Pressman Slides - Software Engineering a Practical Approach 6,e Coming up: What is the complexity?

  9. What is the complexity? public void howComplex(i) { while (i<10) { i++; System.out.printf("i is %d", i); if (i%2 == 0) { System.out.println("even"); } else { System.out.println("odd"); } } } Coming up: What is the complexity V(G)?

  10. What is the complexity V(G)? public void howComplex() { int i=20; while (i<10) { System.out.printf("i is %d", i); if (i%2 == 0) { System.out.println("even"); } else { System.out.println("odd"); } } } V(G) = 2 decisions + 1 = 3 Coming up: Output from JavaNCSS

  11. Output from JavaNCSS NCSS = Non Commenting Source Statements CCN = cyclomatic complexity number Better Tool Found

  12. Better Tool Found (Nov 2009) • RefactorIt • http://sourceforge.net/projects/refactorit/ • http://www.aqris.com/display/A/Refactorit • Provides Cyclomatic Complexity many other metrics, and refactoring tools • Comment density • Coupling • Depth of inheritance, • …

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