Checkstyle

Checkstyle is a development tool to help programmers write Java code that adheres to a coding standard. It automates the process of checking Java code to spare humans of this boring (but important) task. This makes it ideal for projects that want to enforce a coding standard.

Checkstyle is highly configurable and can be made to support almost any coding standard. An example configuration files are supplied supporting the Sun Code Conventions, Google Java Style.

FindBugs

FindBugs is a static analysis tool that examines your class or JAR files looking for potential problems by matching your bytecodes against a list of bug patterns. With static analysis tools, you can analyze software without actually running the program.

PMD

In the facts, PMD is a very powerful tool which works a little bit like Findbugs, but inspect directly the source code, and not the bytecode (btw. PMD can work with plenty of languages). The goal is globally the same, find patterns which can lead to bugs using static analysis. So why use Findbugs and PMD at the same time ? Well, even if Findbugs and PMD share globally the same goals, their inspecting methods are different. So PMD can sometimes find bugs which Findbugs wont, and vice versa. Additionally it includes CPD, the copy-paste-detector. CPD finds duplicated code in Java, C, C++, C#, PHP, Ruby, Fortran, JavaScript, PLSQL, Apache Velocity, Ruby, Scala, Objective C, Matlab, Python, Go, Swift and Salesforce.com Apex.

Lint

“The Android lint tool is a static code analysis tool that checks your Android project source files for potential bugs and optimization improvements for correctness, security, performance, usability, accessibility, and internationalization.”

As the official site said, Android Lint is another static analysis tool, dedicated this time to Android. It is extremely powerful, and can give great piece of advice to improve the quality of your code.