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This article mainly explains: Java core technology
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preface
After so many years of Java development, combined with the usual interview Java developers experience, I think the JavaSE aspect is mainly to master the following content.
1. The JVM
For those new to Java, knowledge of the JVM does not have to be deep, but a brief 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 think the things to know are:
2. Java running
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 one is how to execute Java programs from 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, whether there were any missing files, etc.
This allows you to really develop solutions to all the weird and potentially environment-related problems.
The knowledge to master here includes:
3. Data types
There’s not much to say about this, but it’s all about basic types and object types in Java.
Learn more about automatic conversion in the JDK, including boxing and unboxing, and avoid type equality judgment after boxing.
Key points:
4. Objects and instances
In this regard, developers need to understand the concepts and differences between class and Instance, which is a foundation of Java’s object-oriented nature.
The main points are:
Class and Instance concepts
Instance creation process:
Points to note:
5. Access control
Public protected Default Private decorates classes, methods, and fields.
6. 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.
7. The concept of object-oriented programming
This is a core Java concept that should be mastered by any Java developer.
Many of the features or knowledge points in Java are related to Java object-oriented programming concepts.
In my opinion, a good developer needs to know more than just the features themselves.
It is also important to know how these objects are represented in Java’s object-oriented programming concepts, so that developers can better grasp the Java development language, as well as other object-oriented programming languages.
Here is just a brief list, the main knowledge points include:
8. static
Static properties are also frequently used in Java daily development. You need to understand the usage of the static keyword, as well as the use of other keywords, such as whether it can be used together with the keywords such as abstract and final.
The main things to master are:
9. Basics
Here mainly lists some scattered, no system classification of some Java knowledge points.
It is also used in daily development. In fact, there are a lot of this content, just temporarily summarized these several here:
Include:
10. Collection framework
This is a need to master the part, do Java development, it can be said that there is no collection framework, this is very important, here collated Java collection interview questions and answers you must be clear.
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) :
Collection framework system: basic Collection, Map
Specific Set implementation content, List, Set, Map specific implementation, internal structure, special methods, applicable scenarios, etc
The use of the collections-related utility classes, Collections, etc
11. Exception framework
Exceptions may not get that much attention in Java development, as best practices in exception handling detail.
In general, there is no great impact on the overall operation of the program after directly throwing or catching exceptions. However, in enterprise design and development, the design and handling of exceptions are often related to the robustness of the system as a whole.
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.
There are not many knowledge points to master in this part, mainly including:
Abnormal system:
Throwable Exception RuntimeException Error RuntimeException specifies the difference between RuntimeException and common Exception
12. 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:
The basic IO system includes InputStream, OutputStream, Reader/Writer, file reading, various stream reading, NIO concept, specific use methods and use scenarios.
13. 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; You must be clear about the Java multithreaded interview questions and answers.
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.
14. The network
Java also provides apis for directly operating TCP and UDP protocols.
In cases where network performance needs to be emphasized, TCP/UDP can be directly used for communication.
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.
15. 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.
17. Use Maven
Maven is not in Java either, but Maven is revolutionary and brings great convenience to Java development. Here are 30 Maven commands you must be familiar with.
From the introduction and management of dependencies, to the updating of development processes and release outputs, to the updating of versions, using Maven can greatly simplify the complexity of the development process, resulting in significant time savings.
Maven has become standard for Java developers. So I use Maven as a basic knowledge base for Java developers.
18. Generics
This is a new concept that JDK5 is starting to introduce and is actually a syntax candy.
There is some convenience in writing Java code, the general application or business development, just simple use, do not necessarily need to define generics such operations.
However, developing some basic common components will be used, so you can look at this section as needed, generally as long as you know how to use it.
19. The annotation
Also introduced after JDK5, meta-annotations are something you have to understand.
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.
20. RMI
RMI is the RMI invocation interface for remote Invocation. RMI is the RMI invocation interface for remote invocation.
However, in the case of cross-language support, other means such as WebService are needed.
In general, applications do not need to use RMI, but they can be used in certain situations, such as in one project where I used RMI to remotely start and stop applications.
21. JNI
Java Native Interface allows you to call Native Interface methods in Java. It is generally used to call C/C++ code.
One thing to note is the path to load so/ DLL files in Java. Calling the interface itself is not complicated, but it often takes a lot of time to determine whether or not the required local interface library is loaded.
The above is just a brief introduction to my view and introduction of these Java basics and technical points.
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