Java is an object-oriented programming language for writing cross-platform applications. Java technology has excellent versatility, high efficiency, platform portability and security. It is widely used in PC, data center, game console, scientific supercomputer, mobile phone and Internet. At the same time, it has the world’s largest professional developer community.

1.Java running (Basic requirements)

This one may seem simple, but who doesn’t run Java programs? But most of the time, we just use the IDE to execute Java programs. How does the underlying IDE execute Java programs? Many people don’t.

This is one of the most basic things Java developers need to know. The first thing you learn is how to execute Java programs on the command line, but many people forget this once they learn Java and use the IDE. Why do you want to know this? Knowing the purest way to start Java allows you to analyze how many directories you started, how the execution was named, what the parameters were, and whether there were any missing files when something went wrong. This allows you to really develop solutions to all the weird and potentially environment-related problems.

The knowledge to master here includes:

Javac compiles Java files to class files.

The use of Java commands, where Java classes with package are launched on the command line;

The various paths involved in Java programs (classpath, Java, Library, Path, home directory where Java runs, etc.).

  1. There’s not much to say about data types, but basic types and object types in Java. Basic types: int, long, float, double, Boolean; basic types: int, long, float, double, Boolean; Corresponding Object types: Integer and other types of conversion to basic types, boxing and unboxing Object types: equals, Hashcode, String characteristics.

  2. Access control This is also a foundation of Java encapsulation features, such as public protected Default private for class, method, and field.

  3. Process Control The basics of Java process control, although some of the syntax may not be very common, need to be understood and used where appropriate. Need to master: if, switch, loop, for, while and other flow control syntax.

  4. This is a core Java concept that any Java developer needs to master. Many of the features or knowledge points in Java are related to Java object-oriented programming concepts. In my opinion, a good developer not only needs to understand the features themselves, but also needs to know how these objects are reflected in the concept of Java object-oriented programming, which is more conducive to the developer to master the Java development language, as well as other object-oriented programming languages. The main knowledge points include: object-oriented three characteristics: encapsulation, inheritance, polymorphism; Definition of the respective concepts, what features are represented, the respective usage scenarios, static multiple dispatch, dynamic single dispatch, concept of overloading and use inheritance: interface multiple implementation, base class single inheritance abstraction, abstract class, interface polymorphism: concept of method override and use interface callback

  5. Object and instance, object creation In this respect, developers need to understand the concept of class and instance and the difference between them, this is a foundation of Java object-oriented features. The concepts of Class and Instance; 1. No inheritance: Allocate memory space, initialize variables, call constructors; 2. There is inheritance: handle static actions, allocate memory space, define variables as initializers, from base class to subclass, handle initializations at definitions, execute constructors; Points to note: Static attributes and so on are initialized from base-subclass; Properties associated with the default no-argument constructor.

  6. Static Static attributes are commonly used in Java. Use the Static keyword with other keywords, such as abstract and final. The main things you need to know are: how to define static properties, how to use them, and how to initialize static method definitions and how to use static class definitions and how to use static code blocks and when to initialize them

  7. Basic knowledge points here mainly lists some scattered, no system classification of some Java knowledge points. It is also used in daily development. Equals, HashCode, String/StringBuffer, Final, Finally, Finalize 9. Collection framework this is a need to master the part, do Java development, can say that there is no collection framework, this is very important. But the knowledge is not difficult, but to set the best to understand the internal implementation approach, because it can help you in each different scenario to choose a suitable framework to solve the problem, such as the 1 w a collection of elements, often should undertake the contains operation, know the characteristics of the collection or internal implementation, it is easy to make the right choice. This includes the following (concurrency is not included) : Basic Collection, Map concrete Collection implementation content, List, Set, Map concrete implementation, internal structure, special methods, applicable scenarios and other Collection related utility class Collections usage. 10. Exception framework anomalies may not be as important in Java development. In general, there is no great impact on the overall operation of the program after directly throwing or catching exceptions. However, in enterprise design development, the design and handling of exceptions are often related to the overall robustness of the system. A good system exception handling for the developer should be uniform, avoid scattered exception handling logic; For system, the anomaly should be controlled, and is easy to operations, some abnormal, there should be a response to approach, know how to operational process, so although exception framework is very simple, but for the entire enterprise application development, exception handling is important to deal with abnormal you need to understand the exception system of Java. Exception system: Throwable Exception RuntimeException Error RuntimeException is different from common exceptions and how to handle exceptions.



11.Java IO

IO in Java is not only file read and write so simple, but also includes socket network read and write and so on all input and output operations. For example, reading the content of a Post in a standard HTTP request is an output process, etc…

For IO, Java not only provides basic Input and Output related apis, but also provides some simplified operation apis such as Reader and Writer. It is also important in some development projects (involving a large number of I/O operations), and is also involved in daily development (logging, reading and writing temporary files, etc.).

The main knowledge points in this are:

Basic IO system: including InputStream, OutputStream, Reader/Writer, file reading, various streams reading NIO concepts, specific use methods and use scenarios

12. Multi-threaded concurrency

Multithreading is generally considered a difficult part of Java. Multithreading can effectively improve THE CPU utilization rate, improve the overall system efficiency, especially in the case of a large number of IO operation blocking; But it is also a double-edged sword, if the use is not good, the system not only improve little, or no improvement, but also bring debugging problems between multiple threads.

There are a lot of content in multi-threading, just a brief description of the initial use of multi-threading in Java to master the knowledge, later have the opportunity to separate and detailed some advanced features of the use of the scenario.

Multithreading implementation and startup

Callable is different from runable

Characteristics and comparison of syncrhoized and reentrantLock

The thread pool

Future gets the execution result asynchronously

Concurrent package

lock

.

13. The network

Java also provides apis for directly operating TCP and UDP protocols. In the case that network performance needs to be emphasized, Socket can be directly used to communicate through TCP/UDP. You can see the usage of these apis in the source code of Tomcat, etc. However, TCP is seldom used directly, and frameworks such as MINA and Netty are used for processing. As there is not much development involved in this area, I will not list in detail.

14. Time and date processing

Time and date handling is also tricky for almost every application, but the time related apis prior to JDK8 were not user-friendly. In that era, time frames such as Joda were available. By the time JDK8 was released, the new time-based API basically incorporated the benefits of the other frameworks and was ready to be used directly.

For Java developers, you need to be proficient in using the API to manipulate times and dates.

I will write a later article summarizing the use of the date and time API in JDK8.

XML parsing/JSON parsing

In fact, these two contents are not J2SE inside the content, but in daily development, and other programs interaction, and configuration file interaction, more and more inseparable from these two formats of parsing.

However, as a developer, understanding the principles and methods of XML/JSON parsing can help you choose the right way to make your application more efficient and robust in each specific scenario.

XML: You need to understand the basic principles of DOM parsing and SAX parsing and their applicable scenarios

JSON: You need to understand some common JSON frameworks such as Jackson, FastJson, Gson, etc.

16. Reflection technology

Provide dynamic creation instance, dynamic call method artifact, each big frame zhong love.

17. Using Maven or Gradle

Maven is not in Java either, but Maven is revolutionary and brings great convenience to Java development. From the introduction and management of dependencies, to the updating and release outputs of development processes, and even newer versions, using Maven can save a lot of time by simplifying the complexity of the development process. Maven has become standard for Java developers. So I’m using Maven as a basic knowledge base for Java developers. In the future, I will cover some of my experiences and tips on using Maven, but I won’t go into details here. Gradle is an up-and-comer.

18. Generics

This is JDK5 started to introduce new concept, is actually a syntactic sugar, there’s a convenience when writing Java code, general application or the development of the business, only need a simple to use, does not necessarily need to define a generic such operations, but the development, some basic common components will have access to this part can be in need of looking closer, In general, as long as you can use it simply.

19. Mark

Also introduced after JDK5. Spring is an excellent framework that starts with XML as the standard configuration file. However, with Spring3, and especially with the advent of Spring-Boot, annotations are becoming increasingly popular to simplify XML configuration files, which can save developers a lot of time in XML configuration. But the disadvantage is that annotations are scattered across classes, unlike XML, which has a global understanding and management of all configurations, so there is no way to completely replace XML. For the average developer, it’s ok to use annotations, but some publicly built developers may need to understand the definition and implementation of annotations, so they can review them as needed.

  1. JVM related (including features of each version) For those new to Java, knowledge of the JVM does not necessarily require a deep understanding of the concepts involved. However, for an experienced developer with more than 3 years of Java experience, not knowing the JVM is almost unacceptable. The JVM is the foundation on which Java runs, and it’s hard to believe that someone who doesn’t know anything about the JVM can know everything about the Java language. When I interview developers with more than 3 years of Java experience, the JVM is almost a must-ask question. Of course, the JVM is not the only interview question that determines technical competence, but it is a good example of Java development competence. In the JVM category, I would like to know: JVM memory model and architecture GC principles, performance tuning tuning: Class binary bytecode structure, class loader system, class loading process, instance creation process, method execution process:

Conclusion: People can’t do too many things in this life, so do everything wonderful. Your time is limited, so don’t waste it living someone else’s life. Don’t be trapped by dogma, which is living with the results of other people’s thinking. Don’t let the noise of others’ opinions drown out your own inner voice. And most important, have the courage to follow your heart and intuition. They already know what you truly want to become. Everything else is secondary.

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