Java code coverage tools are of two types: first, tools that add statements to the Java source code and require its recompilation. Second, tools that instrument the bytecode, either before or during execution. The goal is to find out which parts of the code are tested by registering the lines of code executed when running a test.

JaCoCo is an open-source toolkit for measuring and reporting Java code coverage. JaCoCo is distributed under the terms of the Eclipse Public License. It was developed as a replacement for EMMA, under the umbrella of the EclEmma plug-in for Eclipse.

JaCoCo offers instructions, line and branch coverage.

In contrast to Atlassian Clover and OpenClover, which require instrumenting the source code, JaCoCo can instrument Java bytecode using two different approaches:

And can be configured to store the collected data in a file, or send it via TCP. Files from multiple runs or code parts can be merged easily. Unlike Cobertura and EMMA it fully supports Java 7, Java 8, Java 9, Java 10, Java 11, Java 12, Java 13, Java 14, Java 15, Java 16, Java 17, Java 18, Java 19 and Java 20.

JCov is the tool which has been developed and used with Sun JDK (and later Oracle JDK) from the very beginning of Java: from the version 1.1. JCov is capable of measuring and reporting Java code coverage. JCov is distributed under the terms of the GNU General Public License (version 2, with the Classpath Exception). JCov has become open-source as a part of OpenJDK code tools project in 2014.

JCov is capable of reporting the following types of code coverage:

JCov implements two different ways to save the collected data: