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This article mainly explains "what are the knowledge points of JAVA review". The content of the explanation is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "what are the knowledge points of JAVA review"?

JVM

JVM is a necessary skill for every developer. It is recommended to read the classic JVM books in China, which contain basic knowledge such as JVM memory interface, class loading mechanism and so on. Do you think these are familiar in the interview? So instead of reading bits and pieces online, it is better to take a closer look at the book "in-depth understanding of the Java Virtual Machine: JVM Advanced Features and practices (2nd Edition)".

Of course, if you are good at English, it is highly recommended to see the JAVA virtual machine specification released by Oracle. Remember not to be quick when reading. Your accumulation of knowledge is not determined by the number of books you read, but by the depth of reading. So when reading each chapter, you need to understand what you don't understand with the articles on the Internet, and you need to read several articles to understand it, because an article is likely to be wrong. The editor thinks that the credibility order of the articles is self-built domain name > * .github.io > SF > brief Book = blog Garden > CSDN > reprint.

Sorting algorithms and Java collections, utility classes

This classification is something that everyone must master and use skillfully, so why do I put them together? Because tools and collection classes are derived from algorithms, you need to understand why algorithms are required before you prepare for algorithm review. Officially because the sorting algorithm is closely related to our programming. Name two "chestnuts".

So only if you understand the implementation of the sorting method can you make better use of the collection classes in JAVA?

The second "Chestnut", we have all heard of the TopN question, often encountered in the interview, please write about the implementation of TopN, when it comes to the algorithm it is a big top pile, when it comes to JAVA it is an implementation of PriorityQueue, then you understand the TopN problem, know its time complexity, advantages and disadvantages, so can you skillfully use the tool class of JAVA to write more efficient programs?

Sorting algorithms are as important as JAVA collections & utility classes because they are relevant to our daily programming. The interviewer is always asking the sorting algorithm not to embarrass you, but to examine your programming skills. So you need to sort algorithms and basic algorithms with JAVA collection classes, tools to carefully study, so that you can more in-depth understanding of their relationship.

Multithreading and concurrent packages

Multithreading and concurrent packages, the importance will not be repeated, just talk about the learning method. First of all, you have to understand that multithreading is not just as simple as Thread and Runnable, the tools under the entire concurrent package are for multithreading. For multithreaded learning, you must not read a few interview articles, or a few keywords CountDownLatch,Lock Barabara thought that you understood the essence of multithreading, and the editor compiled a big picture.

You need to sort out a big picture for this big picture or yourself, and break down the classes in it, their usage scenarios, their advantages and disadvantages. If you look at it, you will find that it is inseparable from the JAVA collection class and tool class. Then the reason why it is naturally listed as an important point of knowledge is self-evident.

Redis 、 MySQL 、 ElasticSearch

Storage correlation is a tool we usually use, Redis,MySQL,ElasticSearch. Its knowledge points are divided into two aspects, on the one hand, the experience accumulated in the process of using it, and on the other hand, your in-depth understanding of it. So the advice for this place is to consolidate technical knowledge through books. "Redis Design and implementation (Database Technology Series)", "High-performance MySQL" and "ElasticSearch authoritative Guide" are not necessarily books in this field, but if you eat thoroughly, they must be of great help to your understanding of knowledge and program design. There are too many contents in the book, so I still give two "chestnuts".

* Chestnut. When using Redis, you must not only use it as a key-value cache database. The editor learned that one of its five basic types is called sorted set. When the items content in sorted set is greater than 64, both hash and skiplist are used. This will also optimize for sorting and lookup performance. Both add and delete require modification of skiplist, so the complexity is O (log (n)). But if you only look for elements, you can directly use hash, its complexity is O (1), other range operations generally have a complexity of O (log (n)), of course, if it is less than 64, because of the use of ziplist design, its time complexity is O (n). In this way, the query and update reading will become easy, can it be used to achieve the requirements of TopN? Such similar requirements do not require you to check the data and then calculate and operate in memory. For example, our simple weekly ranking and monthly ranking can be implemented by using this data structure, of course, this is not necessarily a solution, but provides a way to solve the problem.

Another "chestnut", PriorityQueue is the priority queue we have known above, so ElasticSearch's query is also used to obtain the priority queue on each shard, and then merge the priority queue, do you understand? This "chestnut" tells us that the algorithm actually works, and if you understand one, you can draw an analogy.

Frame

When you talk about the framework, you think of Spring, and when you say Spring, you think of IOC,AOP. Because everyone is using this framework, you don't need to see anything else about the framework, just take a closer look at Spring. Spring has been out for so long that we already know the basic knowledge. It is important to look at its ideas and principles to solve the problem. Here comes Chestnut again.

For example, if you need to implement something to do when Bean is just initialized, do you need to use InitializingBean? Then how to use it, what its principle is, and what the life cycle of Spring Bean looks like, are explained step by step by specific usage scenarios. This review effect will be better, and then gradually think about each knowledge point involved in more knowledge points, such as AOP inside the Proxy is based on what principles, what are the advantages and disadvantages.

Distributed system

This is an old topic, and it is also a hot topic in recent years. When it comes to distribution, it must have something to do with Dubbo, but we can't just understand Dubbo. First of all, we need to think about the problem it solves and why we introduce the concept of Dubbo.

With the development of business and the growth of the number of users, the number of systems increases, and the call dependency relationship becomes complex. In order to ensure the high availability and high concurrency of the system, the architecture of the system is also slowly moved from the single era to the service SOA era. The emergence of Dubbo, as a RPC, makes it easy for us to build micro-service projects, but we not only have to think about the framework support brought by Dubbo. At the same time, we need to consider the idempotent of services, distributed transactions, Trace location between services, distributed logs, data reconciliation, retry mechanism and so on. At the same time, we need to consider the mechanism of MQ decoupling and pressure sharing, database distributed deployment and sub-database sub-table, current limit, circuit breaker and so on. So the final summary is not only to look at the use of Dubbo, the principle, but also to consider the upstream and downstream and some system design problems, this relative knowledge point is more, can be aimed at the above points one by one.

Design pattern

There are many design patterns, but only a few are commonly used. This place can be prepared in two places.

1. To apply what you have learned, design patterns are not memorized, but used. Usually pay more attention to think about the design of the current project, whether design patterns can be applied, of course, we must first understand the significance of the existence of each design pattern.

2, think about the embodiment of design patterns in the existing framework, the above has talked about how to learn the framework, using Spring for example, it uses more than 9 design patterns, do you know where to use them? If you don't know, try to find them and think about why they are so designed. After finding them all, you will understand the usage and principles of the basic design patterns.

Thank you for your reading, these are the contents of "what are the knowledge points of JAVA review?" after the study of this article, I believe you have a deeper understanding of what the knowledge points of JAVA review have, and the specific use also needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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