Tuning real interview questions
First of all, let's look at a few interview questions about Java tuning that I asked me:
- Why is it faster to use "+" to concatenate strings?
- Why the final keyword does not help inlining now?
- Why does the nested loop principle of small outside and large inside not help performance?
- What are the consequences of instruction reordering?
- What is the most time-consuming operation in a distributed system?
- Why must the code of JDK and high-performance products use JMH?
If I let the editor explain all these questions in detail, the editor will not be able to do it, but these questions will be asked in the interview. You must learn the actual system optimization! With the above questions, let us study a PDF note together, this note will tell the following contents:
- More than 20 optimization techniques: Explain the various methods of Java system performance optimization.
- More than 30 code snippets with "bad smell": actual combat exercises and optimization techniques.
- Commonly used high-performance tools: take Caffeine, Jackson. HikaniCP as examples to explain, and do a certain source code analysis of the reasons for their high performance.
- Easy-to-read code: Explains how to write easy-to-read code from three aspects: code comments, code decomposition and object-oriented.
The following shows you the general content of the PDF, because there is too much content, there is really no way to show all the detailed content for you, the PDF has been sorted out for you
Chapter 1 Java Code Optimization
Chapter 2 String and Number Operations
String (String) and number (Number) are commonly used objects in Java. This chapter discusses the basic usage of these objects and gives ways to use them more efficiently.
This chapter will delve into the best methods for string construction, splicing, formatting, search, and replacement. The String class is so powerful that it is often abused (we discussed the abuse of strings as objects in Chapter 1. , Will continue to be discussed in Chapter 7).
This chapter also studies the performance of digital boxing and unboxing, as well as the performance of precision calculations, and proposes some solutions.
Chapter 3 Concurrent Programming and Asynchronous Programming
Concurrent programming gives play to the processing power of a multi-processor system, allowing multiple tasks to be executed simultaneously, or allowing tasks to be split into multiple tasks for execution. Asynchronous programming can decouple producers and consumers, isolate faults, and cut peaks and fill valleys. Concurrent programming and asynchronous programming are not without cost, they are more complicated to implement, are more prone to errors than serial execution, and may consume more system resources. This chapter explains how to implement efficient concurrent programming and asynchronous programming in a Java system from an efficient perspective.
Chapter 4 Code Performance Optimization
Chapter 2 introduces the efficient usage of String and Number. Chapter 3 introduces concurrent programming to improve system performance. This chapter lists some performance optimization techniques. These skills are widely used in business systems or basic software systems as a way to improve system performance.
Chapter 5 High Performance Tools
This chapter introduces commonly used Java open source tools based on enterprise applications and microservice systems. These tools are characterized by powerful functions and good performance. Applying these tools in projects can improve system performance and enhance code maintainability. This chapter briefly analyzes these open source tools and understands how they can maximize performance.
Chapter 6 Java Annotation Specification
In order to improve the maintainability of the system, Javadoc is an indispensable tool. Javadoc is used to describe the role of classes, methods or fields, and is generally divided into three paragraphs. .
- The first paragraph: a summary description, usually in one sentence or--paragraph to briefly describe the role of the type, ending with a period in English. The summary description is very important, it will appear in the Javadoc index page, introduction page, and the method summary list of the class.
- The second paragraph: a detailed description, usually with-paragraph or multiple paragraphs to describe the role of this type in detail. If you want to describe the implementation process of a class or method, you can add a description of the implementation process after describing the role of the class and method.
- The third paragraph: document annotation, used to mark the author, creation time, reference category and other information.
Javadoc supports the use of HTML to write, and also supports the use of Javadoc Tag. This chapter focuses on the built-in tags provided by Javadoc.
Chapter 7 Readable Code
The project code is "write once, read many times". Readers include code writers, architects, reviewers, and later maintainers. It can make reading code easier and help enhance the maintainability of the project or product. Code readability is an important prerequisite for the application of various software engineering methods, object-oriented practices, refactoring, and new technologies to the project. If the code is difficult to read, then all these methods and theories are difficult to implement in the project; It is difficult to maintain, so performance optimization is impossible to talk about.
Chapter 8 JIT Optimization
Compile the program source code through Javac and convert it into Java bytecode. JVM translates the bytecode into corresponding machine instructions through a template, reads in one by one, and interprets and translates one by one. The execution speed must be faster than executable binary bytecode The program is much slower. In order to improve the execution speed, JIT technology is introduced.
JIT is an important part of JVM. JIT finds hot execution code by analyzing program code, compiles part of bytecode into machine code and saves it for the next call. For smaller methods, inline expansion will be tried. This chapter will introduce the concept of JIT, how to influence JIT through configuration, and introduce JITWatch to observe whether code is optimized by JIT.
In most cases, applications rarely consider JIT optimization, which is an automatic process. However, for tools or key service classes with extremely high performance requirements, you can still consider the impact of JIT on code optimization, and sometimes performance can be improved by hundreds of times.
Chapter 9 Code Review
This chapter lists 31 code snippets. Some code snippets need to be fine-tuned to improve performance or readability, and some code snippets do not achieve the expected function at all, or may make errors when running in certain scenarios. Readers can first read the code snippets to have their own judgment, and then compare the subsequent answers.
Chapter 10 ASM runtime enhancements
Chapter 11 JSR269 Compile Time Enhancements
JSR269 (Pluggable Annotation Processing API) has been supported since Java 6, and its main function is to process the source code when Java is compiled. We are familiar with Lombok, JMH introduced in this book, Selma object mapping & replication tools, etc., all belong to the application of JSR269. Spring Boot's configuration metadata (Configuration Metadata) also uses JSR269. Business systems can also define their own JSR269 annotations to implement code generation and source code modification to enhance Java system functions.
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