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javacompiler-constructioninterpreterjit

How can java use Compiler

I studied somewhere that to execute on different processor architectures Java is interpreted. If it would use compiler then there would be some (Machine Code) instructions which would be specific to processor architectures and Java would be platform dependent. But since java use interpreter it is processor architecture independent.

My question is how can the java use JIT (Just In Time) Compiler? Doesn't the processor's architectures affect it? If it doesn't affect it, then why doesn't it affect it?

Solution

  • There isn't just one JIT compiler. There is a different one for each architecture, so there's one for Windows 32-bit, one for Windows 64-bit etc.

    Your Java code is the same across all platforms. That is compiled into byte code by the Java compiler. The byte code is also the same across all platforms.

    Now we run your Java program on Windows 32-bit. The JVM starts up and it interprets the byte code and turns that into machine code for that architecture. Note that that JVM is specifically for this architecture.

    If we run your program on another architecture, another variation of the JVM will be used to interpret the byte code.

    That's why you see all these different download links when you download the JRE:

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