We, as a developers, sometimes, make mistakes or add bugs to our code without realizing. For this reason static analyzers are a handy tool to apply during our builds or during our code verification processes.

One of these tools is Error Prone.

Error Prone is Google’s Java bug detection and static analysis tool. It is integrated into the Java compiler and catches bugs at compile time. It supports plugin checks for project-specific enforcement.

Basically, it is a tool created by Google for code analysis and error detection for the Java language. It is integrated inside the compiler and tries to detect bugs in compilation time.

But, let’s see and example. Imagine we have a program with the next line of code:

String.format("Param A: {}, param B: {}, param C: {}", paramA, paramB, paramC);

Obviously, it is not correct and the error comes from, maybe, a transformation between a previous log message to a different kind of message. The compiler is not going to complain because it is a string message and it is not a syntax error. But, the truth is there is an error.

When we try to compile the program with Error Prone, we are going to receive a compilation error message like this:

error: [FormatString] extra format arguments: used 0, provided 3
String.format("Param A: {}, param B: {}, param C: {}", paramA, paramB, paramC);              ^
(see http://errorprone.info/bugpattern/FormatString)

We can see clearly and without any doubts there is an error. Even, a link to the error description is provided.

The proper code should be:

String.format("Param A: %s, param B: %s, param C: %s", paramA, paramB, paramC);

The easiest way to start using the tool, it is to add the maven plugin to our pom.xml file:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.3</version>
    <configuration>
        <compilerId>javac-with-errorprone</compilerId>
        <forceJavacCompilerUse>true</forceJavacCompilerUse>
        <source>8</source>
        <target>8</target>
    </configuration>
    <dependencies>
        <dependency>
            <groupId>org.codehaus.plexus</groupId>
            <artifactId>plexus-compiler-javac-errorprone</artifactId>
            <version>2.8.1</version>
        </dependency>
        <dependency>
            <groupId>com.google.errorprone</groupId>
            <artifactId>error_prone_core</artifactId>
            <version>2.0.19</version>
        </dependency>
    </dependencies>
</plugin>

For more options, just go to the installation instructions page.

The project is open source and you can see all the code in the official repository: error-prone.

I am not saying that it is going to solve all your problems but, at least, it is another tool to increase our code quality and avoid silly mistakes.