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This article is about how to learn JVM. The editor thinks it is very practical, so share it with you as a reference and follow the editor to have a look.

What is JVM?

Introduction to JVM: JVM is the abbreviation of Java Virtual Machine, which is translated into Java virtual machine in Chinese. It is a specification for computing devices. It is a fictional computer, which is realized by simulating various computer functions on the actual computer. To put it simply, JVM is used to parse and run Java programs.

Java has a very important feature, "platform independence", which is implemented using JVM. The Java language only needs to generate the object code (bytecode) running on Jvm to run without modification on a variety of platforms, because JVM itself shields platform-specific information, allowing Java to "compile once, run everywhere".

Second, why learn JVM?

Learn JVM for no more than the following reasons:

1. Program tuning

Different programs (business scenarios) require different Jvm configurations, such as setting different garbage collectors, setting memory configuration and share of new and old belts, and so on. Different configurations have different effects on the operation of programs. The default configuration of Jvm can only ensure that the program can "run", and wanting to "run well" or even "run better" is one of the most important factors in learning Jvm.

2. Troubleshoot the running problems of the program

Some programs may encounter a variety of problems when they are used online, and these problems are usually fatal, such as memory overflow, slow running of programs caused by deadlocks, and so on, and these problems are easy to be ignored in the development and small concurrent testing stages, so learning Jvm can help you sweep away the "stubborn diseases" in the system at a critical time.

3. Master the foundation and principle of program execution.

That is what many people say: we should not only "know what it is", but also "know why".

4. Avoid some mistakes when writing code

For example, avoid overloading calls to variable length parameters (specific examples will be given later).

5. Deal with the interview

I have to say that this is also one of the purposes for many people to learn, and of course it is also a positive driving force, if you understand the "catfish effect".

6. Master the general mechanism of other languages

Another powerful thing about JVM is that it can run not only Java programs, but also Scala, Clojure, Groovy, and the popular Kotlin these days. By learning JVM, you can understand the common mechanisms of these languages, and even let these languages share an ecosystem.

Third, how to learn JVM effectively?

The knowledge points of JVM are as follows:

1. The composition of JVM

Only by understanding the components of JVM, can we really understand the five parts of JVM,JVM: heap, virtual machine stack, local method stack, program counter, method area. Later articles will introduce the specific uses of the five parts.

2. Multiple garbage collection algorithms

There are many garbage collection algorithms in Jvm, and the advantages and disadvantages of different algorithms are different, such as: tag removal algorithm and replication algorithm, clearly marked algorithm will produce a variety of space fragments, replication algorithm divides memory into two pieces, although the performance is very good, but only one piece can be used at a time, and the space of memory is wasted, is there a relatively perfect algorithm? The answer must be yes, because of the space, the following article will explain in detail.

3. Various garbage collectors

There are many Jvm garbage collectors, such as the earliest version of the serial collector Serial, the oldest collector, it is a new generation of collector using replication algorithm, it is a single-threaded collector, it must suspend all other worker threads until the end of the Serial collector collection ("Stop The World"). There are also CMS (Concurrent Mark Sweep) collectors that aim to obtain the shortest recovery pause time, and the more cutting-edge G1 (Garbage-First) collectors.

To learn these collectors, on the one hand, to configure appropriate collectors for your own program, on the other hand, the setting parameters of each collector are different. After learning the configuration of these collectors, you can set the optimal running matching parameters for the program.

4. JVM analysis tools

Jvm analysis tools are used to troubleshoot the defects of the program and find out where the problems lie, so as to ensure the stable operation of the program. Jvm analyzer is divided into command line tools (officially called experimental tools, but stability is indisputable), and view analysis tools, the former is certainly better than the latter, but the latter is based on the former. Each tool will be explained in depth later in this series.

5. Java class loading mechanism

Java class loading mechanism, which is about the loading and running mechanism of Java classes in Jvm, is of great help in understanding how Java works. This is also a very interesting point in learning Java. You can see that the whole process of running Java is completely transparent, giving people a sense of "control". This is naturally supported by the Java language, so you will find the language Java very interesting.

6. JVM commonly used to optimize configuration

In fact, the biggest benefit of learning Jvm is to use these common configurations of Jvm to make your program run more efficiently, so it is essential for this aspect of learning.

Thank you for reading! This is the end of the article on "how to learn JVM". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, you can share it for more people to see!

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