A development system having a client which employs a virtual machine for executing programs written in the Java programming language is described. The client executes a "compiled" (i.e., bytecode or pseudo-compiled) Java program, which has been created by compiling a Java source code program or script with a Java compiler. The pseudo-compiled program comprises the bytecode emitted by the compiler. The development system further includes a just-in-time compiler which natively compiles each pseudo-compiled method of a Java program on a "just-in-time" basis--that is, compiles each method as it is actually used into native machine code for a target microprocessor. Methods which are unused are left uncompiled (i.e., left as bytecode). During program execution, when a method call is made from interpreted code, the system employs an "invoker" slot of the callee. When a method call is made from compiled code, the system employs a "compiled code" slot of the callee. As the addresses for the slots themselves remain unchanged, a method which has been compiled need not be recompiled when a callee method it invokes is itself compiled. In this manner, a method (caller) calling another method (callee) need not know whether it is calling is an interpreted method or a compiled method.