Compiling Java just in time

The Java programming language promises portable, secure execution of applications. Early Java implementations relied on interpretation, leading to poor performance compared to compiled programs. Compiling Java programs to the native machine instructions provides much higher performance. Because traditional compilation would defeat Java´s portability and security, another approach is necessary. This article describes some of the important issues related to just-in-time, or JIT, compilation techniques for Java. We focus on the JIT compilers developed by Sun for use with the JDK (Java Development Kit) virtual machine running on SPARC and Intel processors. (Access the Web at www.sun. com/workshop/java/jit for these compilers and additional information.) We also discuss performance improvements and limitations of JIT compilers. Future Java implementations may provide even better performance, and we outline some specific techniques that they may use