Wednesday, February 20, 2013
Difference between JIT and JVM in Java - Interview Question
Main difference between JIT and JVM is that, JIT is part of JVM itself and used to improve performance of JVM. JIT stands for Just In time compilation and JVM stands for Java Virtual Machine. JVM is a virtual machine used in Java programming platform to execute or run Java programs. Main advantage of JVM is that, it makes Java platform independent by executing byte codes. Java source code is compiled into class files, which contains byte code. These byte codes are then executed by JVM. Now here comes JIT. Since execution of byte code is slower than execution of machine language code, because JVM first needs to translate byte code into machine language code. JIT helps JVM here by compiling currently executing byte code into machine language. JIT also offers caching of compiled code which result in improved performance of JVM. by the way difference between JVM and JIT is also a good Java interview question to ask. Well, this is just a simple explanation, JIT is lot more complex than this. There are sophisticated algorithm which helps JIT to pick most executed code for compiling into machine code. Earlier we have seen difference between JRE and JDK and in this post we will understand difference between JVM and JIT. Let's see next section for more difference between JIT vs JVM.
Here are couple of more differences between JVM and JIT in Java programing platform :
1) Main difference between JVM and JIT is there purpose, main goal of JVM is to provide platform independence while objective of JIT is to improve performance of JVM, by compiling more code into machine language. Just keep in mind that this compilation also takes time, so translating all code into native code is not worth doing. That's why JIT mostly compile frequently used code into native code.
3) Another difference between JIT and JVM is that, JIT is part of JVM. One example of JIT is Oracle's Hotspot JIT which comes with Hotspot JVM.
2) At last, JVM is older concept than JIT. JIT actually get invented to improve performance of JVM.
That's all on difference between JVM and JIT in Java. As I said, JIT is part of JVM and used to improve JVM performance by dynamically compiling or translating Java byte codes into native machine language code during execution time.
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