What is the difference between PMD, FindBug, checkstyle, and sonar? What is the focus of each?

It can be said that they are all code static analysis tools, but the focus is different.
pmd: Based on source code analysis, it is mainly oriented to safe coding rules, such as "avoid declaring variables with the same name", including style classes, type usage, etc., and has certain data flow analysis and path analysis capabilities.
checkstyle: Based on source code, similar to pmd, but more focused on coding syntax style, and its analysis depth is not as deep as pmd.
findbugs: Based on bytecode analysis, a large number of data flow analysis techniques are used, focusing on runtime error detection, such as null pointer references, etc., and the analysis depth is greater than the previous two.
sonar: Positioned as a code quality platform, it does not perform code analysis itself, but can integrate various static analysis tools and other software development and testing tools, and based on the result data of the integrated tools, according to a certain quality model, such as iso-9126, the quality of the software to evaluate.

https://www.zhihu.com/question/19620900

http://blog.csdn.net/ml5271169588/article/details/6975701