Understanding Just In Time Java Compiler

The Just-In-Time (JIT) java compiler comes with along the Java Virtual Machine (JVM). The bytecode created by the JVM are converted to the machine code or the native code during the execution of the application.

The conversion is made possible by only the JIT compiler. This speeds up the execution process and moreover this makes the code portable to any machine.

The JIT compiler maintains a table called the V-table. The V-table has the addresses of the methods of the classes in the bytecode. If there is any derived class the address of the derived class is stored instead of the original class.

The V-table actually has two tables one for the addresses of the bytecode and another for the native code that is created using the bytecode. During the first time execution of a method, it is converted to the native code by the JIT compiler and address of the native code for that particular method is stored in the table. During subsequent execution the native is called for execution and this improves the speed of the execution.