Warming up the JVM

Compileable languages, such as C++, are so named because the provided code is entirely binary and can be executed directly on the CPU. Because the interpreter (loaded on the destination machine) compiles each line of code as it runs, Python and Perl are referred to as interpreted languages. In Figure 9.1, we showed that Java is in the middle; it compiles the code into Java bytecode, which can then be turned into binary when necessary.

It's for long-term performance optimization that Java doesn't compile the code upon startup. Java builds frequently called code by watching the program run and analyzing real-time method invocations and class initializations. It might even make some educated guesses based on past experience. As a result, the compiled code is extremely quick. The main caveat for having an optimal execution time is to call the function many times.

Before a method can be optimized and compiled, it must be called a particular number of...