The real Java post BATJ interview questions collected by Ali senior architects for half a year: all in this article

It's the peak period of job interviews again. Recently, many netizens are asking for interview questions from Dachang. It happened that I had this sort of work in my computer before, so I posted it and shared it with everyone.

These questions are the questions that netizens were asked in interviews with first-line Internet companies such as Baidu, Xiaomi, LeTV, Meituan, 58, Cheetah, 360, Sina, and Sohu. Familiarity with the knowledge points listed in this article will greatly increase the chances of passing the first two rounds of technical interviews.

The information on the Internet is divided according to the company. It is a bit difficult to find specific knowledge points. I will sort them out according to the knowledge points. I want to see which one can be found quickly. I hope it can help everyone. I wish you all The job search went smoothly.

 

java interview questions

Proficiency in Java is very important. Large companies not only require you to use several APIs, but also require you to be familiar with the principles of source code implementation, and even to know what are the shortcomings, how to improve, and some algorithms related to Java. , Design patterns and so on.

Java basic interview knowledge points

• The difference between == and equals and hashCode in java
• How many bytes does int, char, and long occupy?
• The difference between int and integer
• Tan Tan's understanding of java polymorphism
• String、StringBuffer、StringBuilder区别
• What is an inner class? The role of inner classes
• The difference between abstract class and interface
• The meaning of abstract classes
• Application scenarios of abstract classes and interfaces
• Can an abstract class have no methods and attributes?
• The meaning of the interface
• The difference between extends and super in generics
• Can the static method of the parent class be overridden by the child class
• The difference between process and thread
• The difference between final, finally, finalize
• Serialization method
• The difference between Serializable and Parcelable
• Can static properties and static methods be inherited? Can it be rewritten? And why?
• Design intent of static inner classes
• Understanding of member inner classes, static inner classes, local inner classes and anonymous inner classes, and the application in the project
• Talk about the understanding of kotlin
• The difference between closure and local inner class
• The way and principle of converting string to integer

Analysis of Java basic interview questions:

Analysis of Java basic interview questions:

(Two) java in-depth source-level interview questions (difficulty)

• Under what circumstances will objects be disposed of by the garbage collection mechanism?
• Tell me about common encoding methods?
• How many bytes does the Chinese in utf-8 encoding occupy; how many bytes does int type?
• What is the difference between static proxy and dynamic proxy, and in what scenarios?
• Java's exception system
• Talk about your understanding of analysis and dispatch.
• Modify the signature of the equals method of object A, then when using HashMap to store this object instance, which equals method will be called?
• What is the mechanism to achieve polymorphism in Java?
• How to serialize a Java object into a file?
• Talk about your understanding of Java reflection
• Talk about your understanding of Java annotations
• Talk about your understanding of dependency injection
• Talk about the principle of generics and give an example
• Understanding of String in Java
• Why should String be designed to be immutable?
• The equal and hashCode methods of the Object class are overridden. Why?

Principle source code analysis:

Principle source code analysis:

(3) Data structure

• Introduction to common data structures
• What do you know about concurrent collections?
• List java collections and the inheritance relationship between collections
• Collection class and collection framework
• Introduction to container classes and the difference between them (container classes estimate that many people have not heard the word, Java containers can be divided into 4 parts: List list, Set collection, Map mapping, tool class (Iterator iterator, Enumeration enumeration class, Arrays and Collections), you can check out this blog post Java container class http://alexyyek.github.io/2015/04/06/Collection/ for details  )
• The difference between List, Set, Map
• Implementation and storage of List and Map
• The realization principle of HashMap
• HashMap data structure?
• HashMap source code understanding
• How to put data in HashMap (explained from the perspective of HashMap source code)?
• How to implement HashMap by hand?
• The realization principle of ConcurrentHashMap
• Comparison of ArrayMap and HashMap
• HashTable implementation principle
• Concrete implementation of TreeMap
• The difference between HashMap and HashTable
• The difference between HashMap and HashSet
• How do HashSet and HashMap determine that the set elements are duplicated?
• How to prevent collisions when implementing Hash in Set
• The difference between ArrayList and LinkedList, and application scenarios
• The difference between array and linked list
• Specific implementation of depth-first traversal and breadth-first traversal of binary trees
• Heap structure
• The difference between heap and tree
• What is the difference between heap and stack in memory (answer hint: you can answer from two aspects: data structure and actual implementation)?
• What is deep copy and shallow copy
• Handwritten linked list reverse code
• Talk about the understanding of the tree, B+ tree
• Talk about the understanding of the graph
• Determine whether the singly linked list is a ring or not?
• Linked list flip (ie: flip a single necklace table)
• Combine multiple singly ordered linked lists (assuming that they are all increasing)

Data structure analysis:

Data structure analysis:

(4) Thread, multi-thread and thread pool

• Three ways to start threads?
• The difference between thread and process?
• Why have threads instead of just processes?
• The difference between run() and start() methods
• How to control the number of threads that a method allows concurrent access to?
• The difference between wait and seelp methods in Java;
• Talk about the understanding of wait/notify keywords
• What causes thread blocking?
• How to close the thread?
• Talk about the synchronization method in java
• How to ensure data consistency?
• How to ensure thread safety?
• How to achieve thread synchronization?
• Can two processes require writing or reading at the same time? How to prevent synchronization of processes?
• List of operations between threads
• The life cycle of objects in Java
• Synchronized usage
• Principle of synchronize
• Talk about the understanding of Synchronized keywords, class locks, method locks, and reentry locks
• Multithreaded access and function of static synchronized method
• Two synchronized methods in the same class, the problem of simultaneous access by two threads
• The principle of volatile
• Talk about the usage of volatile keyword
• Talk about the role of volatile keyword
• Talk about the understanding of NIO
• The difference between synchronized and volatile keywords
• The difference between synchronized and Lock
• Comparison of ReentrantLock, synchronized and volatile
• Internal implementation of ReentrantLock
• lock principle
• Four necessary conditions for deadlock?
• How to avoid deadlock?
• Will object locks and class locks affect each other?
• What is a thread pool and how to use it?
• Java's concurrency, multithreading, threading model
• Talk about the understanding of multithreading
• What are the issues to pay attention to in multi-threading?
• Talk about your understanding of concurrent programming and give examples
• Talk about your understanding of the multi-thread synchronization mechanism?
• How to ensure the safety of multi-threaded reading and writing of files?
• The principle of multi-threaded resumable transmission
• Realization of Resumable Transmission

Thread, multi-thread and thread pool interview analysis:

Thread, multi-thread and thread pool interview analysis:

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