How to add -Xlint:unchecked to my Android Gradle based project?

This is what worked for me: (in your project's build.gradle)

allprojects {
    gradle.projectsEvaluated {
        tasks.withType(JavaCompile) {
            options.compilerArgs << "-Xlint:unchecked" << "-Xlint:deprecation"
        }
    }
}

Disclaimer: Even though this answer has more than 10 upvotes, it does not address the problem in the context of an Android project. However, Google finds this question in the context of non-Android projects. Thus, I keep this answer for those folks.

According to JavaCompile, the following seems to be solution:

compileJava {
    options.encoding = 'UTF-8'
    options.compilerArgs << "-Xlint:unchecked" << "-Xlint:deprecation"
}

If you want it to have for the test cases, use compileTestJava

compileTestJava {
    options.encoding = 'UTF-8'
    options.compilerArgs << "-Xlint:unchecked" << "-Xlint:deprecation"
}

Put this in your build.gradle file (root directory):

allprojects { // Projects
   gradle.projectsEvaluated {
      tasks.withType(JavaCompile) {
         options.encoding = 'UTF-8'
         options.compilerArgs << "-Xlint:unchecked" << "-Xlint:deprecation"
      }
   }
}