1<?xml version="1.0" encoding="UTF-8" ?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> 3<html xmlns="http://www.w3.org/1999/xhtml" lang="en"> 4<head> 5 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> 6 <link rel="stylesheet" href="resources/doc.css" charset="UTF-8" type="text/css" /> 7 <link rel="shortcut icon" href="resources/report.gif" type="image/gif" /> 8 <title>JaCoCo - Coverage Counter</title> 9</head> 10<body> 11 12<div class="breadcrumb"> 13 <a href="../index.html" class="el_report">JaCoCo</a> > 14 <a href="index.html" class="el_group">Documentation</a> > 15 <span class="el_source">Coverage Counters</span> 16</div> 17<div id="content"> 18 19<h1>Coverage Counters</h1> 20 21<p> 22 JaCoCo uses a set of different counters to calculate coverage metrics. All 23 these counters are derived from information contained in Java class files 24 which basically are Java byte code instructions and debug information 25 optionally embedded in class files. This approach allows efficient on-the-fly 26 instrumentation and analysis of applications even when no source code is 27 available. In most cases the collected information can be mapped back to 28 source code and visualized down to line level granularity. Anyhow there are 29 limitations to this approach. The class files have to be compiled with debug 30 information to calculate line level coverage and provide source highlighting. 31 Not all Java language constructs can be directly compiled to corresponding 32 byte code. In such cases the Java compiler creates so called <i>synthetic</i> 33 code which sometimes results in unexpected code coverage results. 34</p> 35 36<h2>Instructions (C0 Coverage)</h2> 37 38<p> 39 The smallest unit JaCoCo counts are single Java byte code instructions. 40 <i>Instruction coverage</i> provides information about the amount of code that 41 has been executed or missed. This metric is completely independent from source 42 formatting and always available, even in absence of debug information in the 43 class files. 44</p> 45 46<h2>Branches (C1 Coverage)</h2> 47 48<p> 49 JaCoCo also calculates <i>branch coverage</i> for all <code>if</code> and 50 <code>switch</code> statements. This metric counts the total number of such 51 branches in a method and determines the number of executed or missed branches. 52 Branch coverage is always available, even in absence of debug information in 53 the class files. Note that exception handling is not considered as branches 54 in the context of this counter definition. 55</p> 56 57<p> 58 If the class files haven been compiled with debug information decision points 59 can be mapped to source lines and highlighted accordingly: 60</p> 61 62<ul> 63 <li>No coverage: No branches in the line has been executed (red diamond)</li> 64 <li>Partial coverage: Only a part of the branches in the line have been 65 executed (yellow diamond)</li> 66 <li>Full coverage: All branches in the line have been executed (green diamond)</li> 67</ul> 68 69<h2>Cyclomatic Complexity</h2> 70 71<p> 72 JaCoCo also calculates cyclomatic complexity for each non-abstract method and 73 summarizes complexity for classes, packages and groups. According to its 74 definition by 75 <a href="http://hissa.nist.gov/HHRFdata/Artifacts/ITLdoc/235/title.htm">McCabe1996</a> 76 cyclomatic complexity is the minimum number of paths that can, in (linear) 77 combination, generate all possible paths through a method. Thus the 78 complexity value can serve as an indication for the number of unit test cases 79 to fully cover a certain piece of software. Complexity figures can always be 80 calculated, even in absence of debug information in the class files. 81</p> 82 83<p> 84 The formal definition of the cyclomatic complexity v(G) is based on the 85 representation of a method's control flow graph as a directed graph: 86</p> 87 88<blockquote> 89 <p> 90 v(G) = E - N + 2 91 </p> 92</blockquote> 93 94<p> 95 Where E is the number of edges and N the number of nodes. JaCoCo calculates 96 cyclomatic complexity of a method with the following equivalent equation based 97 on the number of branches (B) and the number of decision points (D): 98</p> 99 100<blockquote> 101 <p> 102 v(G) = B - D + 1 103 </p> 104</blockquote> 105 106<p> 107 Based on the coverage status of each branch JaCoCo also calculates covered and 108 missed complexity for each method. Missed complexity again is an indication 109 for the number of test cases missing to fully cover a module. Note that as 110 JaCoCo does not consider exception handling as branches try/catch blocks will 111 also not increase complexity. 112</p> 113 114<h2>Lines</h2> 115 116<p> 117 For all class files that have been compiled with debug information, coverage 118 information for individual lines can be calculated. A source line is 119 considered executed when at least one instruction that is assigned to this 120 line has been executed. 121</p> 122 123<p> 124 Due to the fact that a single line typically compiles to multiple byte code 125 instructions the source code highlighting shows three different status for 126 each line containing source code: 127</p> 128 129<ul> 130 <li>No coverage: No instruction in the line has been executed (red 131 background)</li> 132 <li>Partial coverage: Only a part of the instruction in the line have been 133 executed (yellow background)</li> 134 <li>Full coverage: All instructions in the line have been executed (green 135 background)</li> 136</ul> 137 138<p> 139 Depending on source formatting a single line of a source code may refer to 140 multiple methods or multiple classes. Therefore the line count of methods 141 cannot be simply added to obtain the total number for the containing class. 142 The same holds true for the lines of multiple classes within a single source 143 file. JaCoCo calculates line coverage for classes and source file based on the 144 actual source lines covered. 145</p> 146 147<h2>Methods</h2> 148 149<p> 150 Each non-abstract method contains at least one instruction. A method is 151 considered as executed when at least one instruction has been executed. As 152 JaCoCo works on byte code level also constructors and static initializers are 153 counted as methods. Some of these methods may not have a direct correspondence 154 in Java source code, like implicit and thus generated default constructors or 155 initializers for constants. 156</p> 157 158<h2>Classes</h2> 159 160<p> 161 A class is considered as executed when at least one of its methods has been 162 executed. Note that JaCoCo considers constructors as well as static 163 initializers as methods. As Java interface types may contain static 164 initializers such interfaces are also considered as executable classes. 165</p> 166 167</div> 168<div class="footer"> 169 <span class="right"><a href="@jacoco.home.url@">JaCoCo</a> @qualified.bundle.version@</span> 170 <a href="license.html">Copyright</a> © @copyright.years@ Mountainminds GmbH & Co. KG and Contributors 171</div> 172 173</body> 174</html> 175
