JVM Learning Notes (i) JDK&JRE&JVM

Jdk:java Development ToolKit (Java SDK), including the Java Runtime Environment JRE (Java Runtime envirnment), a bunch of Java tools (javac/java/ JDB, etc.) and Java-based class libraries (that is, Java APIs include Rt.jar).
The JDK includes the JRE primarily because of the tools and examples available in the JDK and requires JRE support to run.

Jre:java Runtime enviromental (Java Runtime Environment). That is what we call the Java platform, all Java programs must be under the JRE to run. Includes JVM and Java core class libraries and support files. It does not include development tools-compilers, debuggers, and other tools-compared to the JDK.

Jvm:java virtual mechinal (Java vm). The JVM is part of the JRE, a fictional computer that is implemented by simulating various computer functions on a real computer. JVM has its own perfect hardware architecture, such as processor, stack, register, etc., also has the corresponding instruction system. The main task of the JVM is to interpret its own instruction set (that is, bytecode) and map it to the local CPU's instruction set or system call to the OS. The Java language is a cross-platform operation, in fact, different operating systems, using different JVM mapping rules, so that it is independent of the operating system, the completion of cross-platform. The JVM does not care about the upper Java source files, it only focuses on the class file generated by the source file. The composition of the class file includes the JVM instruction set, the symbol table, and some subsidy information.
Very good surface of the relationship between the three JDK,JRE,JVM:

The difference between JDK and JRE can be learned from the clear view of the various logic modules contained in the Java platform

For the JVM's own physical structure, we can take a bird's eye view:

For the study of the JVM, it seems to me that so many parts are most important:

• The entire process of compiling and executing Java code
• JVM memory management and garbage collection mechanism

JVM Learning Notes (i) JDK&JRE&JVM