A method and apparatus to guarantee type safety in multithreaded programs, and to guarantee initialization safety in well-behaved multithreaded programs. A plurality of bytecodes representing a program are received and examined to identify bytecodes defining object creation operations and object initialization operations. Upon execution of the plurality of bytecodes, memory barrier operations are performed subsequent to the performance of both the object creation operations and the object initialization operations. This guarantees type safety, and further guarantees initialization safety if the program is well-behaved. Optimization algorithms may also be applied in the compilation of bytecodes to improve performance.