For example, in sun/security/rsa/PSSParameters.java#L184, it takes the form of

        if (PSSParameterSpec.class.isAssignableFrom(paramSpec)) {
            return paramSpec.cast(spec);
        } else {
            throw new InvalidParameterSpecException
                ("Inappropriate parameter specification");
        }

but in fact it should be "paramSpec.isAssignableFrom(PSSParameterSpec.class)". isAssignableFrom means is-parent-of and you can only cast an object of a child class to that of a parent class.