Ali Senior Technical Expert: What technical capabilities should a Java programmer with 3 years of experience have at each stage

1. Basic grammar

This includes the use of static, final, transient, foreach loops, and so on. If you answer static modifiers, modifiers I will think you qualified, if you answer static blocks, I will think you are good, if you answer static inner class I will think you are very good, and if you answer static guide package I will be very satisfied with you, because I can see that you are very keen on research technology.

In my most in-depth interview, I remember being asked directly about the underlying implementation of the Volatile key. (By the way, the interview and the intervieware themselves are relative, and the interviewer’s ability to ask this question also makes the interviewer feel that the interviewer is also a technical person, which makes the interviewer feel good about the company. I ultimately chose the company that asked this question), and don’t be too picky — simple questions tell you a lot about your skills, and breadth is often more important than depth, remember.

2, collections,

It’s very important and it’s a must-ask. List, Map, Set, etc.

ArrayList, LinkedList, Hashtable, HashMap, ConcurrentHashMap, HashSet, etc. ConcurrentHashMap is one of the most frequently asked questions in interviews, probably because it can generate so many questions. For ConcurrentHashMap, I would like to offer three answers or research directions:

(1) Lock segmentation technique of ConcurrentHashMap.

(2) Whether the read of ConcurrentHashMap should be locked and why.

(3) Whether the iterator of ConcurrentHashMap is strongly consistent or weakly consistent.

3, the framework

It’s a cliche. It’s an interview question. In general, I will ask you about the framework you are using in your project, and then I will give you some scenarios to ask you how to use the framework, such as how I want to do something when Spring initializes the bean, how I want to do something when the bean is destroyed, the difference between $and # in MyBatis, etc. All these are practical. Usually accumulated well, how much learning framework use details naturally are not a problem.

If you answered the above questions well, the interviewer will often ask in depth how the framework works. One of the most frequently asked questions is the implementation principle of Spring AOP. Of course, this is very easy to do in two sentences, even if you don’t have to prepare for it. The weirdest I encountered was when I was asked to draw a UML diagram of Spring’s actual Bean plant, an insightful question I was, of course, absolutely unable to answer

4. Database

Nine times out of ten, the database will ask. Some basic differences like and all, left JOIN, several indexes and their differences are not discussed, the more important is the database performance optimization, if the database performance optimization is ignorant, then have time, or suggest you spend a day or two before the interview specifically to prepare the SQL foundation and SQL optimization content.

However, the database is not to worry about, a company often has many departments, if you are not familiar with the database and the basic technology is very good, nine chengdu will ask you, it is estimated that you will be put into the database use is not very high requirements of the department exercise.

5. Some Web issues

Java is primarily web-oriented, so some questions about the Web are also mandatory.

The two most common questions I get are:

Discuss several ways to implement distributed Session.

The four commonly used answers are naturally very satisfying to the interviewer.

Another commonly asked question is: Talk about the difference and connection between Session and Cookie and how Session is implemented. In addition to these two questions, the content of web.xml is the key. Filters, servlets, and listeners are not only clear about how they are implemented, but at least how they are used. In addition, some details such as get/ POST differences, forward/ redirect differences, and HTTPS implementation principles may also be examined.

6. Data structure and algorithm analysis

Data structure and algorithm analysis, for a programmer, is better than never and definitely comes in handy in the workplace. Array, linked list is the basis, stack and queue in-depth but also not difficult, tree is very important, more important tree AVL tree, red black tree, can not understand their specific implementation, but to know what is a binary search tree, what is a balanced tree, AVL tree and red black tree difference. I remember an interview, a certain interviewer and I were talking about the index of the database, he asked me: do you know what kind of data structure the index uses?

I think I got the Hash table. Wrong. Do you know why trees are used? I replied that because Hash tables are likely to have a lot of conflicts, it can greatly increase the time complexity of searching for tens or even hundreds of millions of data faces. And the tree is more stable, basic guarantee up to 20 or 30 times can find the data you want, the other party said not completely right, finally we still communicate about this problem, I also understand why to use a tree, here do not say, friends think index why to use a tree to achieve it?

As for algorithmic analysis, forget it. I was asked in an interview what sort method collections.sort used. Of course in order to show my erudite, analysis of the algorithm also have a certain amount of research (⊙﹏⊙) B, I still stiff upper lip said a may be bubbling sort bar. The answer, of course, is no. For those interested, check out the source code for the collections.sort method, which uses a sort called TimSort, or enhanced merge sort.