checker/tests/nullness/generics/GenericsBounds4.java

import org.checkerframework.checker.nullness.qual.*;

public class GenericsBounds4 {
  class Collection1<E extends @Nullable Object> {
    public void add(E elt) {
      // :: error: (dereference.of.nullable)
      elt.hashCode();
    }
  }

  Collection1<? extends @Nullable Object> f1 = new Collection1<@NonNull Object>();
  // :: error: (assignment)
  Collection1<@Nullable ? extends @Nullable Object> f2 = new Collection1<@NonNull Object>();
  Collection1<@Nullable ? extends @Nullable Object> f3 = new Collection1<@Nullable Object>();

  void bad() {
    // This has to be forbidden, because f1 might refer to a
    // collection that has NonNull as type argument.
    // :: error: (argument)
    f1.add(null);

    // This is forbidden by the Java type rules:
    // f1.add(new Object());

    // ok
    f3.add(null);
  }
}