import edu.umd.cs.findbugs.annotations.NonNull;
import edu.umd.cs.findbugs.annotations.CheckForNull;

public class AnnotationDemo {

    @NonNull
    private Object returnNonNull() {
        // ERROR: returnNonNull() may return null, but is declared @Nonnull
        return null;
    }

    @CheckForNull
    private Object returnNullable() {
        return null;
    }

    public void testReturnNullable() {
        Object obj = returnNullable();
        // ERROR: Possible null pointer dereference due to return value of called method
        System.out.println(obj.toString());
    }

    private void argumentNonNull(@NonNull Object arg) {
        System.out.println(arg.toString());
    }

    public void testArgumentNonNull() {
        // ERROR: Null passed for non-null parameter of argumentNonNull(Object)
        argumentNonNull(null);
    }

    public void testNullableArgument(@CheckForNull Object arg) {
        // ERROR: arg must be non-null but is marked as nullable
        System.out.println(arg.toString());
    }

}