Describe the problem you'd like to have solved

Currently the javadoc has no links to JDK classes, e.g. java.lang.Object. This makes browsing it slightly inconvenient.

Describe the ideal solution

This could be solved by specifying the JDK link the Gradle build file:

javadoc {
    options.links 'https://docs.oracle.com/javase/8/docs/api/'
}

Alternatives and current work-arounds

Alternatively, or additionally you could also specify a JDK toolchain only for the javadoc task which takes advantages of the lastest JDK javadoc features (such as a search bar), without having to change the lowest Java version this projects supports.

I have implemented an experimental implementation for this here (this also partially addresses #487), feel free to try it out:

1. Build with gradlew javadoc
2. Open lib/build/docs/javadoc/index.html in your browser

I don't have much experience with Gradle, so I am not sure if this is properly implemented. However, let me know if I should create a pull request for the branch.