Why I cannot cast oracle BLOB from native java Blob

...
ResultSet rs = ...
java.sql.Blob myfile = rs.getBlob("field")
java.io.OutputStream os = ((oracle.sql.BLOB) myfile).getBinaryOutputStream();

java.lang.ClassCastException

java.io.OutputStream os = ((oracle.sql.BLOB) myBlob).setBinaryStream(1L);