What is the evolution and change of the Java virtual machine?

1. Sun Classic/Exact VM

Class VM (JDK 1.0)

The world’s first commercial Java virtual machine

Pure Execute Java code in interpreter mode

Object search based on handle

Exact VM (JDK 1.2)

Accurate memory management: the virtual machine can know the data at a certain location in the memory Specific type

2, HotSpot VM

Default virtual machine in Sun/OracleJDK and OpenJDK

The most widely used Java virtual machine

Since the HotSpot virtual machine is currently the most widely used and is currently the default virtual machine for OracleJDK and OpenJDK, the content analysis in the following article is mainly focused on this virtual machine.

Execute the java -version command on the terminal as follows:

$ java -version
java version "1.8.0_191"
Java(TM) SE Runtime Environment (build 1.8.0_191-b12)
Java HotSpot(TM) 64-Bit Server VM (build 25.191-b12, mixed mode)

3. Mobile/Embedded VM

Java ME virtual machine

4. BEA JRockit/IBM J9 VM

These two virtual machines were once known as the "three major commercial Java virtual machines" together with the HotSpot virtual machine.

JRockit

Focus on server-side applications

Does not contain an interpreter, all codes are compiled and executed by a just-in-time compiler

J9 VM

Separation of duties and modularity are better than HotSpot VM

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