Java job interview focus: Java+JVM+MySQL+framework+algorithm, the salary increase depends on it

Preface

In fact, I told you before that I really don't like the behavior of memorizing various questions and memorizing all kinds of questions when the interview is approaching . I am very opposed to it! I think this method is extremely extreme, and it is useless at all in front of a slightly experienced interviewer.

Some fans left a message with me and said: "Our company's current interview is directly a computer test. As long as the computer is tested, there will be a chance for the next interview, so the test questions on the back are useless."

Judging from the current industry situation, the difficulty of interviews for Java programmers is constantly increasing, and the technical requirements for programmers are getting higher and higher. The requirements for academic qualifications in some departments of large factories are also gradually decreasing, which shows that the industry is still taking Technical speaking.

In summary, the technology is constantly being updated, the difficulty of interviews is increasing, and there is still a lot to learn. Do not interview for the interview, and do not think that you will build airplanes and rockets during the interview. And friends who work in Dachang summarized the following interview key points, I hope you can use the time of more than two months to prepare for the interview in advance, and never do to deal with the interview!

Due to space limitations, the next part of the content will be shown in screenshots. The full version can be obtained after the keyword "learning" by private message after [forward + follow]!

Java

Java basic study notes

 

Interview focus

• Hashmap source-level mastery, expansion, red-black tree, minimum tree capacity, hash conflict resolution, some interviewers will ask questions from the soul, such as why it is a red-black tree, and other trees can’t; why is it tree at 8 Change, 4 can’t it, wait
• ConcureentHashMap, segment lock, how to segment, the difference between hashmap and hashmap, performance, etc.
• HashTable, synchronization lock, this piece may ask you what has been improved after the synchronized keyword 1.6, and how to improve these
• ArrayList advantage, expansion, when to use
• Advantages of LinkedList, when to use it, the difference with arraylist, etc.
• The difference between the basic type and the packaging type involves automatic boxing and unboxing, how to do it, and the principle
• String, StringBuffer, StringBuilder which is safe
• I have been asked about the difference in string encoding. I think it’s easier to overlook a point
• What is generic and how to use generic
• Can static modify threadLocal, why? This question was actually quite daunting when I heard it
• What are the Comparable and Comparator interfaces, and the difference
• What is the principle of polymorphism? It feels easy to be asked
• The interviewer asked me how I understood interfaces and abstract classes. I said that interfaces correspond to functions and abstract classes correspond to attributes. Then the interviewer gave me his opinion, saying that abstract classes are more biased towards a template~ Then I exchanged Let’s take a look
• How to reflect and set the value of an object's private field
• What is the difference between fail-fast and fail-safe
• The realization principle of synchronized and lock optimization?
• The realization principle of volatile?
• Semaphore for Java?
• The difference between synchronized in static method and ordinary method?
• How to realize that all threads wait for an event to occur before executing?
• CAS? What are the shortcomings of CAS and how to solve it?
• What is the difference between synchronized and lock?
• How is Hashtable locked?
• List, Map, and Set interfaces are taking element teachers, what are the characteristics of each
• How to implement a counter thread-safely
• The producer-consumer model requires hand-written code, but you still need to know
• Singleton mode, hungry man style, lazy man style, thread-safe approach, judge whether the instance is empty twice, and what is the function of each judgment.
• Thread pool, this is still very important, it is used a lot in production, four thread pool types, its parameters, understanding of the parameters is very important, how to set corepoolSize, how to set maxpoolsize, keep-alive various, interview with Meituan The official discussed the setting of the blocking queue in production, he said that he generally set it to 0 to prevent users from blocking
• The difference between cyclicbarrier and countdownlatch, personal understanding of horse racing and point rocket
• Thread callback, I was asked to design an RPC, how to implement it, it is practical to the callback thing
• What is the difference between sleep and yeild method
• The volatile keyword, visibility.
• Use scenarios of optimistic lock and pessimistic lock
• Common realization of pessimistic lock: lock synchronized retreentlock
• Optimistic lock: CAS MVCC
• The realization of the read-write lock, the first eight bits and the last eight bits of the 16-bit int are used as the flag bits for the read lock and write lock respectively
• The conditions of the deadlock, how to remove the deadlock, how to observe the deadlock.
• I hope you can take a good look at the principle of reflection, how to determine the class, how to adjust the method
• RPC framework, synchronous and asynchronous, response time, these have been asked, but also let the design
• Synchronous, asynchronous, blocking, and non-blocking have been encountered in convincing interviews. It is best to find some application scenarios to understand

 

JVM

Study notes

 

 

Interview focus

• The memory model and partitions need to be detailed on what to put in each area.
• Partitions in the heap: Eden, survival (from + to), old age, their own characteristics.
• Object creation method, object memory allocation, object access location.
• Two judgment methods of GC
• The three collection methods of GC: the principles and characteristics of mark removal, mark sorting, and copying algorithms. Where are they used? If you are asked to optimize the collection method, what ideas do you have?
• What are the GC collectors? Features of CMS Collector and G1 Collector
• When do Minor GC and Full GC happen respectively?
• JVM memory is divided into several areas, what is the role of each area?
• How to judge whether an object is alive? (or how to judge GC objects)
• What are the methods of garbage collection in java?
• The class loader parent delegation model mechanism?
• Java memory model, java class loading process?
• What are class loaders and what are the class loaders?
• Briefly describe the java memory allocation and recovery strategy and Minor GC and Major GC

 

MySQL

Study notes (basic + performance optimization + architecture design)

 

Interview focus

• The four characteristics of transactions (ACID) atomicity, consistency, isolation, and durability?
• Concurrency of transactions? Transaction isolation level, what problems each level will cause, which level is MySQL by default?
• What is the difference between the three common MySQL storage engines (InnoDB, MyISAM, MEMORY)?
• MySQL's MyISAM and InnoDB storage engines, transaction and lock levels, and their respective applicable scenarios?
• The order of execution of different elements of the query statement (where, jion, limit, group by, having, etc.)
• Why use B+ tree for index, what is the difference between B+ tree and B- tree
• The default transaction level of mysql, which transaction levels are there in total
• Some statements of mysql, these must be mastered
• mysql lock, row lock, table lock, when lock occurs, how to lock, principle
• Database optimization, the leftmost principle, horizontal sub-table, vertical sub-table
• What is a temporary table and when is the temporary table deleted?
• The difference between MySQL B+Tree index and Hash index?
• SQL query statement to determine which type of index to create? How to optimize the query?
• The difference between clustered index and non-clustered index?
• What locks are there (optimistic locks, pessimistic locks), and how to add exclusive locks when selecting?
• What are the differences between non-relational databases and relational databases, and what are the advantages?
• Three paradigms of database, design data table according to a certain scene?
• 7 questions about database read-write separation, master-slave replication, master-slave replication analysis?
• Use explain to optimize sql and index?
• How to solve MySQL slow query?
• What are inner joins, outer joins, cross joins, Cartesian products, etc.?
• What locks does mysql have, the principle of deadlock determination and specific scenarios, and how to solve the deadlock?
• What are the usage scenarios of varchar and char?
• mysql high concurrency environment solution?

 

Common framework (Spring+MyBatis+Kafka+Netty)

 

 

 

Algorithm (big factory must ask)

Study notes (including problem-solving ideas)

 

Interview focus

7.1 Sorting algorithm

• The eight sorting algorithms are really interview darlings
• The most frequently tested quick sort and merge sort
• Which sorting algorithms are stable and which are unstable
• Heap row should also be mastered

7.2 Tree

• Restore the tree according to the traversal result, recursively
• K-th largest binary search tree
• The path of the tree whose sum is k
• Level traversal
• Restore tree based on level traversal and post-order traversal
• Mirror tree
• Tree depth
• Balanced binary tree

7.3 Linked List

• Reverse linked list
• Entrance of the linked list ring
• Intersection point of cross-linked list
• Copy of complex linked list
• Binary search tree becomes a doubly linked list

7.4 Backtracking algorithm

• Walk the maze
• Game clearance

7.5 Recursive Algorithm

• Step up
• Broken steel bar

7.6 Knapsack problem

• The most loaded stuff

7.7 Greedy Algorithm

• Coverage problem
• Time issue

 

to sum up

Remember, the most important thing in an interview is: brush the questions and brush the questions and brush the questions and brush the questions every day, don't hug the Buddha~

The above content is the focus of some interviews. There is a good chance that Gold Nine Silver Ten will be asked, but other related technical points, such as middleware, distributed, design patterns, etc. also need to be mastered. The editor has also compiled a pdf for only Everyone learns ways of thinking

If necessary, you can get it in the private message keyword "learning" on the homepage after [forward + follow]!

Part of the surface is sorted out: