What should we learn in Java?

In fact, I learned Java for such a long time and blindly learned how to understand it. I did not have a deep research on how to understand it. I saw this elder brother's learning Java essay, I think we should learn many of his ideas as follows:

 

Briefly record some java tips during this time:
1. There is nothing to say about the syntax, which can be done in an hour or two;
2. Every exception must be handled, which is too troublesome. This will not only affect the development efficiency, but also easily lead to exception loss;
3. JDK, JRE, and JVM must be able to clearly understand their concepts;
4. Although the package and import mechanisms are similar to the namespace, they are used differently. First, the folder must have a corresponding relationship. Second, the full path or the shortest path must be used.. Net can use half of the using path and use half of the path;
5. To learn Java, you must start with javac.exe. it is easier to understand the consistency between java.exeand javac.exe and JRE versions. Otherwise, you will be waiting to get mad;
5. Classloader is very interesting. The delegate model is simple and practical, but it has never understood the implementation principle of context classloader;
6. Java's multithreading and serialization are really convenient to use;
7. Jar files, ear files, and war files are all in ZIP format;
8. Learning Java is the process of learning various API specification. It is very efficient to query spec in case of problems;
9. J2EE is a set of standards. jsp, Servlet, and EJB are all running in containers. Comparing EJB with Windows Services may be helpful;
10. JNDI is a part of j2se and provides an abstract description of the Naming Service for ease of use;
11. Registering a JDBC driver in the form of class. forname () is a bit incredible;
12. The attribute naming format of Javabean is still a little different from that of C;
13. Struts, hibernate, and spring are successful frameworks at different levels in the Java architecture and are easy to understand;
14. JMS is independent of different message transmission mechanisms and is easy to use, which means there are more exceptions;
15. Learning Java is just learning the architecture. The framework class library is a lot like a cow's hair. After learning Java, I learned what software design is ......
16 .......

Haha, just write something as a summary of learning Java some time ago. Although Java is not a very elegant language, it is indeed quite interesting.
In the Java world, there is no black box at all. You can thoroughly study anything. Basically, it is open source, which is indeed quite good.