How to use @Nullable and @Nonnull annotations more effectively?

Question

I can see that @Nullable and @Nonnull annotations could be helpful in preventing NullPointerExceptions but they do not propag

Answer 1

If you use Kotlin, it supports these nullability annotations in its compiler and will prevent you from passing a null to a java method that requires a non-null argument. Event though this question was originally targeted at Java, I mention this Kotlin feature because it is specifically targeted at these Java annotation and the question was "Is there a way to make these annotations more strictly enforced and/or propagate further?" and this feature does make these annotation more strictly enforced.

Java class using @NotNull annotation

public class MyJavaClazz {
    public void foo(@NotNull String myString) {
        // will result in an NPE if myString is null
        myString.hashCode();
    }
}

Kotlin class calling Java class and passing null for the argument annotated with @NotNull

class MyKotlinClazz {
    fun foo() {
        MyJavaClazz().foo(null)
    }
}  

Kotlin compiler error enforcing the @NotNull annotation.

Error:(5, 27) Kotlin: Null can not be a value of a non-null type String

see: http://kotlinlang.org/docs/reference/java-interop.html#nullability-annotations