Java files should be located in a directory that ends with the fully qualified name of the package.
For example, classes in the package edu.oswego.cs.dl.util.concurrent should be located in: .../edu/oswego/cs/dl/util/concurrent.
If necessary, the check may be suppressed by annotating the enclosing package declaration with @com.google.errorprone.annotations.SuppressPackageLocation, for example:
// package-info.java @com.google.errorprone.annotations.SuppressPackageLocation package com.google.my.pkg;
Note that package annotations must be located in a package-info.java file that must be built together with the package.