1. A method of executing bytecodes in a data processing system, said method comprising the steps of: a) receiving a plurality of bytecodes, each bytecode defining an operation, wherein said plurality of bytecodes comprises at least first and second subsets of bytecodes, and wherein each bytecode belonging to said first and second subsets defines an object creation operation and an object initialization operation respectively; b) identifying bytecodes belonging to at least one of said first and second subsets in said plurality of bytecodes; and c) executing said plurality of bytecodes, wherein the operation defined by each bytecode is performed, and so that i) when the operation defined by at least one bytecode belonging to said first subset is performed, a memory barrier operation is performed thereafter, and ii) when the operation defined by at least one bytecode belonging to said second subset is performed, a memory barrier operation is performed thereafter.