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2: Chapter 1: understanding JVM specification 1: introduction to JVM;
2022-07-05 23:11:00 【Small withered forest】
explain :
(1)JVM brief introduction , know JVM;
Catalog
3. Virtual machine is “Java Platform independence ” The protection of ;
1.JVM summary ;
(1) Virtual machine can be regarded as a computer system , But it is simulated by software ;
(2) On a real physical machine , Mainly from CPU Execute instruction set ;;; stay JVM in , Simulate instruction set through software ;
……………………………………………………
(1) The right part : We wrote java Source code (.java file ), And then through java compiler ( Such as javac Wait for the order , Or by IDEA Tools such as ) Compile it into java Bytecode (.class file );
● This process is the development process ;
(2) The left part : When we compile into .class After the document , This Java Platform runtime environment ( namely JVM) Through the class loader (Class Loader), Put the bytecode file (.class file ) Load into the virtual machine ;
● natural , When loading , Will verify and authenticate bytecode files ( such as , Verify whether it conforms to the virtual machine specification 、 Whether the format is correct );
● When loading bytecode files , Also mount java Class library ( It refers to some basic things that must be provided by the virtual organism 、 Necessary support , such as : Basic data types 、if-else and for Treatment of circulation 、 Basic java Safe handling ,JNI With some hardware processing and so on );
(3) The middle part on the left : When we finish loading , The virtual machine will give these to Java Interpreter ;
● Java The interpreter will interpret the bytecode and execute ; It will also involve just in time compilers (JIT);
● The runtime is much more complex than shown in this figure ;;; The running environment must first allocate memory , And then execute .class Bytecode ( You will use the bytecode execution engine ), Garbage collection is also needed , Consider concurrent processing , Safety treatment ;
(4) Lower left : If you need to interact with hardware or operating system ( Such as through JNI Interact with the outside world ), The virtual machine will come out ; namely java Programs interact with virtual machines 、 Virtual machines interact with operating systems 、 Then interact with the hardware through the operating system ;
2.JVM The main function ;
3. Virtual machine is “Java Platform independence ” The protection of ;
(1) stay Windows On the system 、Linux On different systems, such as the system ,Java Virtual machines are different ;
(2) The same program we developed , Compile it into .class After the document ;
● Throw it into Linux On the system , There is Linux Version of JVM To run ;;; Throw it into Windows On the system , There is Windows Version of JVM To run ;
● Look at it like this , Actually Java It's not really platform independent ; It's just that different virtual machines on different platforms have shielded us ;
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2:第一章:认识JVM规范1:JVM简介;
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