1. 1 Java : Fundamentals

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14. 14 وابستگی کمپایلرها به پلتفرم ها

15. 15 ایده ای برای استقلال از پلتفرم

16. 16 معرفی JVM

17. 17 فرایند اجرای کد جاوا

18. 18 فرایند اجرای کد جاوا (ادامه)

19. 19 فرایند اجرای کد جاوا (ادامه)

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23. 23 JVM و JRE،JDK  Java Development Kit (JDK): This includes ALL the basic Java framework packages, a compiler (javac), JRE, a JVM, debugger etc. in short all you need to develop, debug, compile and run our Java program.  Java Runtime Environment (JRE): This is a subset of the JDK. It does not include a debugger, compiler, and framework classes. This includes the bare minimum that a computer needs in order to run a.class file.

24. 24  Java Virtual Machine (JVM): JVM is a part of JRE. The.class file is passed over to JVM which then runs the program. The JRE ensures that the code does not violate any of the security restrictions. Remember that the byte-code (.class file) is not directly run on the host machine; it needs to be converted to the host machine's language. This conversion is done by the JVM. While converting the JVM ensures the security and may also optimize the code.

25. 25  There are many commercial JVMs available in the market - different JVMs have different capabilities, and varying degree of performance. In order to produce efficient, code with minimum delay a JVM needs to have great amount of intelligence built into it. Which would also make the JVM larger in size. Remember that for a Java program to run, the JVM must be loaded in the memory, and it is obvious that a large sized JVM would need much more computer resources than a compact one. So there has to be a fine balance between the size of a JVM and its capabilities. This is why a Java program is always 30-70% slower than equivalent C++ program.

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