BAT often ask Java foundation 39 often meet questions
Java multithreading interview questions
100 Java Interview Questions
Multithreading, concurrency, and threading fundamentals
Java interview questions for experienced programmers
The underlying JVM and Garbage Collection interview questions
3 years of work experience in Java interview questions
Java basic Concepts interview questions
Java Collections Framework interview questions
Java IO and NIO interview questions
Java Best Practices interview questions
Date, Time and Calendar interview questions
Unit test JUnit interview questions
Interview questions about OOP and design patterns
A variety of other Java interview questions
Java development job interview questions are summarized
First, Java foundation
Second, the Java IO
Third, Java Web
Fourth, the JVM
Open source framework
Vi. Multi-threading
7. Network communication
MySql database
9. Design mode
Ten, algorithm
Concurrency and performance tuning
Ali Advanced Java interview questions and answers
Interview topic:
Interview questions and reference answers:
BAT often ask Java foundation 39 often meet questions
1. The size of the eight basic data types, and their encapsulation classes
2. Reference data types
3. Can the Switch use string as a parameter
4. Equals ==
5. Automatic packing, constant pool
6. What are the common methods of Object
7.Java four kinds of references, weak and weak soft virtual, used in the scene
8. The role of Hashcode
9. What hashCode does for HashMap
10. Why override the hashCode method?
11. Differences between ArrayList, LinkedList and Vector
12. The difference between String, StringBuffer and StringBuilder
13. Features and usage of Map, Set, List, Queue and Stack
14. Differences between HashMap and HashTable
Implementation of HashMap in JDK7 and JDK8
16. The difference between HashMap and ConcurrentHashMap, the underlying source of HashMap
17. Can ConcurrentHashMap completely replace HashTable
18. Why is HashMap thread unsafe
19. How to use HashMap thread safely
20. Whether HashMap still generates an infinite loop under multiple concurrent conditions
21. Differences between TreeMap, HashMap, LindedHashMap
22.Collection package structure, the difference between Collections
23.try? catch? Finally, try has a return in finally
24.Excption and Error package structure, OOM what situation you have encountered, SOF what situation you have encountered
25.Java(OOP) Object oriented three characteristics and meaning
26.Override and Overload
27. The difference between Interface and Abstract class
28.Static? class? And non? static? The difference between the class
29. Comparison of foreach efficiency with normal for loop
30.Java? IO and NIO
31. How Java reflection works
32. Common features of generics
33. Principles and characteristics of several ways of parsing XML: DOM and SAX
Java1.7 and 1.8,1.9,10 new features
35. Design patterns: singletons, factories, adapters, chains of responsibility, observers, etc
36. The use of JNI
37. The AOP is what
38. The OOP is what
The difference between AOP and OOP
Java multithreading interview questions
1. What is the use of multithreading?
2. How threads are created
3. The difference between the start() and run() methods
4. Difference between Runnable interface and Callable interface
5. Difference between CyclicBarrier and CountDownLatch
The role of the volatile keyword
7. What is thread safety
How to obtain thread dump file in Java
9. What happens to a thread with a runtime exception
How do I share data between two threads
What’s the difference between sleep and wait
12. What is the role of the producer-consumer model
13. What does ThreadLocal do
14. Why wait() and notify()/notifyAll() are called in synchronous blocks
15. What is the difference between wait() and notify()/notifyAll() when giving up object monitors
16. Why use thread pools
17, how to check if a thread has object monitor
The difference between synchronized and ReentrantLock
19. What is the concurrency of ConcurrentHashMap
20. What is ReadWriteLock
21. What is FutureTask
How do I find which thread uses the longest CPU in Linux
Java programming to write a program that will cause a deadlock
24, How to wake up a blocked thread
25. How does immutable objects help multithreading
26. What is multithreaded context switching
27. What happens if the thread pool queue is full when you submit a task
28. What is the thread scheduling algorithm used in Java
What does thread.sleep (0) do
30. What is spin
What is the Java memory model
32. What is CAS
What is the optimistic lock and pessimistic lock
34, What is AQS
Singleton thread safety
36. What does Semaphore do
37, Hashtable size() = “return count”;
38, Thread class constructor, static block is called by which thread
Synchronization method and synchronization block, which is the better choice
40. How can thread pools be used for high concurrency and short task execution times? How can thread pools be used for businesses with low concurrency and long task execution times? How can a business with high concurrency and long business execution time use thread pools?
100 Java Interview Questions
Multithreading, concurrency, and threading fundamentals
1) Can Volatile arrays be created in Java?
2) Can volatile make a nonatomic operation atomic?
3) What is the practice with volatile modifiers?
4) What guarantees do volatile variables provide?
5) Which is easier to write, 10-thread or 2-thread synchronization code?
6) How do you call wait ()? If block or loop? Why is that?
7) What is false sharing in multi-threaded environment?
Java interview questions for experienced programmers
8) What is Busy Spin? Why do we use it?
How to obtain a thread dump file in Java?
10) Is Swing thread-safe?
11) What are thread-local variables?
12) What are the differences between sleep and wait methods in Java?
13) What is an immutable object? How do you create an immutable object in Java?
14) Can we create an immutable object that contains mutable objects?
15) What data types should be used to represent prices in Java?
16) How to convert byte to String?
17) How to convert bytes to long in Java?
18) Can we cast int to a byte variable? What happens if the value is greater than the byte range?
19) Which class contains the Clone method? Is it Cloneable or Object?
20) Is the ++ operator in Java thread safe?
21) Not a thread-safe operation. It involves multiple instructions, such as reading variable values, increasing,
22) A = a + b
23) Can I assign a double to a variable of type long without casting?
24) 3*0.1 == 0.3 will return what? True or false?
25) Which takes up more memory, int or Integer?
26) Why are strings Immutable in Java?
27) Can we use String in Switch?
28) What is a constructor chain in Java?
The underlying JVM and Garbage Collection interview questions
29) The length of an int in a 64-bit JVM is the majority?
30) What are the differences between Serial and Parallel GC?
31) For 32-bit and 64-bit JVMS, is the length of a variable of type int the majority?
32) Difference between WeakReference and SoftReference in Java?
33) How does WeakHashMap work?
34) What does the JVM option -xx :+UseCompressedOops do? Why make
35) How to determine whether a JVM is 32-bit or 64-bit using a Java program?
36) What is the maximum heap memory for 32-bit and 64-bit JVMS?
37) What are the differences between the JRE, JDK, JVM and JIT?
3 years of work experience in Java interview questions
38) Explain Java heap space and GC?
39) Can you guarantee GC execution?
40) How to obtain the memory used by Java programs? What percentage of the heap is used?
41) What is the difference between heap and stack in Java?
Java basic Concepts interview questions
42) What is the difference between “a==b” and “a. quals(b)”?
43) What does a.hashcode () do? What does it have to do with A. als(b)?
44) What is the difference between Final, Finalize and finally?
45) What are compile-time constants in Java? What are the risks of using it?
Java Collections Framework interview questions
46) The difference between List, Set, Map and Queue (answer)
47) The difference between the poll() method and the remove() method?
48) What is the difference between LinkedHashMap and PriorityQueue in Java?
49) No difference between ArrayList and LinkedList?
50) What are the two ways to sort sets?
51) How to print an array in Java?
52) Is LinkedList unidirectional or bidirectional in Java?
53) What tree is used to implement TreeMap in Java? (the answer)
54) What is the difference between Hashtable and HashMap?
55) How does a HashSet in Java work internally?
56) Write code to remove an element while iterating through an ArrayList?
57) Can we write a container class ourselves and use the for-each loop code?
58) Default size of ArrayList and HashMap is majority?
59) Is it possible for two unequal objects to have the same Hashcode?
60) Can two identical objects have different hash codes?
61) What is the difference between Comparator and Comparable in Java?
62) Why do I need to override hashCode when overriding equals?
Java IO and NIO interview questions
63) How to create a ByteBuffer in Java?
Java Best Practices interview questions
64) What best practices do you follow when writing multithreaded programs in Java?
65) Name a few best practices for using Collections in Java
66) Name 5 IO best practices (answers)
67) Name a few best practices for method overloading in Java?
Date, Time and Calendar interview questions
68) Is SimpleDateFormat thread-safe in a multithreaded environment?
Unit test JUnit interview questions
69) How do I test static methods?
70) How to convert a string to an integer in Java?
Interview questions about OOP and design patterns
71) What is the interface? Why use interfaces instead of directly using concrete classes?
72) What is the difference between abstract classes and interfaces in Java?
73) Besides singletons, what other design patterns have you used in production?
74) Under what circumstances is Demeter’s Law violated? Why is this a problem?
75) What is the adapter pattern? When to use it?
76) What are “dependency injection” and “inversion of control”? Why do people use it?
77) What is abstract class? How is it different from an interface? Why have you ever used abstract classes?
78) Which is better, constructor injection or setter dependency injection?
79) What is the difference between dependency injection and engineering patterns?
80) What is the difference between adapter mode and decorator mode?
81) What was the difference between the adapter pattern and the proxy pattern?
82) What is the template method pattern?
83) When to use the visitor pattern?
84) When to use composite mode?
85) What is the difference between inheritance and composition?
86) Describe overloading and overwriting in Java?
87) What is the difference between nested public static classes and top-level classes in Java?
88) What is the difference between composition, aggregation, and association in OOP?
89) Give me an example of a design pattern that conforms to the open close principle.
90) What is the difference between abstract factory pattern and prototype pattern?
91) When to use the premium mode?
A variety of other Java interview questions
What is the difference between a nested static class and a top-level class?
93) Can you write a regular expression to determine if a string is a number?
94) What is the difference between checked and unchecked exceptions in Java?
Throws throws (throws) throws (throws
96) How does Serializable differ from Externalizable in Java?
97) What is the difference between DOM and SAX parsers in Java?
98) Name three new features in JDK 1.7?
99) Name five new features introduced in JDK 1.8?
100) What is the difference between Maven and ANT in Java?
Java development job interview questions are summarized
First, Java foundation
1. Why is the String class final
2. HashMap source code, implementation principle, underlying structure.
List, Set, Queue, Map implementation classes.
4. Describe the respective implementations and differences between ArrayList and LinkedList
5. What are the queues in Java and what are the differences?
6. The difference between class. forName and classloader in reflection.
7. New features of Java7 and Java8
8. The operation efficiency of Java array and linked list structures, in which cases (start from the beginning, start from the end, start from the middle), which operations (insert, find, delete) are efficient.
9. Investigate and locate the problem of Java memory leak: the use of JMAP, JStack, etc.
10. The difference between String, StringBuilder and StringBuffer
11. Differences between hashTable and HashMap
13. Structure of exceptions, run-time exceptions and non-run-time exceptions, for example.
14. A common String method
16. What are the types of Java references
17. Distinction between abstract classes and interfaces
18. Java base types and byte sizes
19. The Hashtable, HashMap, ConcurrentHashMap underlying implementation principle and thread safety.
20. What would you do if you implemented a Map instead of using Java Jdk tools? For a long time, I said HashMap source code, if I do, I will draw on the principle of HashMap, said a HashMap implementation.
21. What about Hash conflicts? What are the ways to resolve hash conflicts?
22. How do you resolve HashMap conflicts with the worst performance? Order n to log n.
23. rehash
24. HashCode () and equals() generate the algorithm and how to rewrite the method.
Second, the Java IO
1. Talk about common classes in IO, byte streams, character streams, interfaces, implementation classes, method blocking.
2. Tell me about the NIO
3. What is the difference between UTF-8 and GBK?
4. When to use byte stream and when to use character stream?
5. Recursively read files under the folder, how to achieve the code?
Third, Java Web
1. The difference and connection between session and cookie, the life cycle of session, and session management when multiple services are deployed.
2. Some issues related to servlets
3. Webservice-related problems
4. JDBC connection, forname mode step, how to declare using a transaction.
5. Configure web. XML without a framework
6. The difference between JSP and servlet
Fourth, the JVM
1. Java memory model and GC algorithm
2. What does JVM performance tuning do
3. Introduce the seven regions in the JVM, and then explain how each region can cause memory overflow.
4. Describes abnormal references to GC and GC Root
5. From the classload loading mode, loading mechanism, from the program runtime data area, to the memory allocation, to the String constant pool, to the JVM garbage collection mechanism, algorithm, hotspot.
6. How the JVM allocates direct memory, how new objects are not allocated on the heap but on the stack, constant pool resolution.
7. The size of the array is placed in the older JVM
8. Access to arrays in the old days
9. GC algorithm, how to GC permanent generation objects, how to deal with GC loops.
10. Who gets GC and when.
11. What if you want to avoid GC
12. What if you want to survive a GC
Open source framework
1. Differences between Hibernate and IBatis
2. Talk about connection pooling in Mybatis
3. Which JAR packages need to be referenced in the Spring framework, and the purpose of these JAR packages
4. Principle of springMVC
5. Meaning of springMVC annotations
6. Spring beanFactory and ApplicationContext
7. Several ways of Spring injection
8. How does Spring implement transaction management
9. springIOC
10. Principles of Spring AOP
Level 1 and Level 2 caches in Hibernate
12. Hibernate principle architecture, five core interfaces, three state transitions of Hibernate objects, transaction management.
Vi. Multi-threading
1. Java calls the difference between start() and run() directly after creating a thread
2. Common thread pool modes and usage scenarios of different thread pools
3. NewFixedThreadPool This thread pool if the number of threads reaches the maximum.
4. Synchronization of communication between multiple threads. Synchronized locks are objects, which can be derived from many specific issues related to synchronized, such as whether an object can be accessed at the same time when different methods of the same class have synchronized locks. Or the effect of a class’s static constructor plus synchronized locks.
5. Understand the meaning of ReentrantLock and the difference between ReentrantLock and synchronized
6. Understanding of the source code of synchronized data structures such as concurrentHashMap and its internal implementation, why it is synchronous and efficient.
7. Understanding and use of thread-safe operation keywords such as AtomicINTEGER and Volatile
8. Communication between threads, wait and notify
9. Use of timed threads
10. Scenario: In a main thread, a large number (many, many) of child threads are required to execute before the main thread is finished. Multiple ways, consider efficiency.
11. The difference between processes and threads
12. What is thread safety?
13. Several states of threads
14. Concurrent, synchronous interfaces or methods
15. Is HashMap thread safe and why is it not? ConcurrentHashMap, thread safe, why safe. What the underlying implementation looks like.
16. Use of common classes under J.U.C. An in-depth look at ThreadPool; Use of BlockingQueue. (take, poll, put, offer) Implementation of atomic classes.
17. A brief introduction to multithreading, starting with creating a thread. And then how do you control the synchronization process, the common methods and structures of multithreading
18. Understanding of volatile
19. There are several ways to implement multithreading. How to do multithreading synchronization?
7. Network communication
1. HTTP is stateless communication. What are the HTTP request methods?
2. Socket communication, and processing of long connection, subcontracting and abnormal connection disconnection.
3. Use of socket communication model, AIO and NIO.
4. The use of socket framework NetTY, and the implementation principle of NIO, why is asynchronous non-blocking.
5. Synchronous and asynchronous, blocking and non-blocking.
6. OSI seven-layer model, including some basic knowledge of TCP and IP
7. Differences between GET and Post in HTTP
8. Describe the relationship between HTTP, TCP, and UDP.
9. Tell me how the browser visited http://www.taobao.com.
10. HTTP protocol, HTTPS protocol, SSL protocol and the complete interaction process;
11. TCP congestion causes fast return, and IP packets are discarded
12. HTTPS processes a process, symmetric encryption and asymmetric encryption
13. What are the characteristics and differences of head
14. Tell me how the browser visited http://www.taobao.com.
MySql database
1. MySql storage engine is different
2. Single index, union index, and primary key index
Mysql > select * from user where user = ‘Mysql’; select * from user where user = ‘Mysql’
4. After dividing tables, you want to make multiple tables with one ID to be self-increasing, which is efficient
5. Configure the master/slave real-time backup synchronization of MySql, and the principle (read the master binlog from the secondary database), read/write separation.
6. Write SQL statements and SQL optimization
7. Index data structure, B+ tree
8. Four characteristics of transactions, and their respective characteristics (atoms, isolation, etc.), how the project solves these problems.
9. Database lock: row lock, table lock; Optimistic lock, pessimistic lock
10. Several granularity of database transactions
11. Difference between relational and non-relational databases
9. Design mode
1. Singleton mode: full and hungry. And delayed loading in Hanzhong, double check.
2. Factory mode, Decorator mode, observer mode.
3. Advantages of factory method mode (low coupling, high cohesion, open and closed principle)
Ten, algorithm
1. Use the random algorithm to generate a number, which requires all the numbers between 1-1000W to be generated.
2. Merge sort of two ordered arrays
3. An array in reverse order
Calculate the positive square root of a positive integer
5. In plain English, common search and sort algorithms and their respective time complexity.
6. Binary tree traversal algorithm
7. DFS and BFS algorithm
9. Basic understanding and implementation of important data structures, such as linked lists, queues and stacks.
10. Sorting algorithms and temporal complexity (why fast sorting is unstable and why your project is still using it)
11. Reverse Polish calculator
12. Hoffman encoding
13. Find trees and red black trees
Concurrency and performance tuning
1. There are 5K requests per second to query the location of the mobile phone number. How to design the algorithm? More requests, say 5W, how do you design the whole system?
2. How does our system support a large number of requests under high concurrency
3. How does the cluster synchronize session status
4. Principle of load balancing
5. If there is a particularly large number of visits to the database, how to do optimization (DB design, DBIO, SQL optimization, Java optimization)
6. If large area of concurrency occurs, how to solve the problem of delayed server response without adding more servers?
7. If there is a performance bottleneck in your project, what do you think it might be and how to solve the problem?
8. How to find the location causing the performance bottleneck and identify the location as the performance bottleneck.
9. Do you use caching in your projects? There is no user non-local cache
Ali Advanced Java interview questions and answers
Interview topic:
1. What are the algorithms of machine learning that you are familiar with? Talk about the processes and differences of these algorithms
2. What are the five layers of the network architecture and what are the protocols in each layer
3, what is the difference between TCP and UDP, if you want to send instant messages should use which protocol
4, TCP connection establishment and disconnection process (three times handshake and four times wave), how to ensure that TCP sent information is correct, and ensure that the order is not tampered with
5. How much do you know about HTTP, what is the difference between HTTP and HTTPS, and how is HTTPS security implemented
6, usually use mysql with what engine
7. What are the features of database transactions
8, what are the possible problems caused by transaction concurrency, what are the isolation levels of the database, what is the default isolation level of mysql, what are the problems that can be avoided by this default isolation level?
9, how to judge whether the SQL query operation is slow SQL, how to optimize
10, the difference between process and thread, communication between processes
What are deadlocks and how to handle deadlocks
12. What are the handling methods for critical sections in process synchronization
Spring MVC, Spring AOP source code
14. Spring loop references
15. Spring Transaction propagation mechanism
16, Java NIO, BIO, AIO, operating system underlying NIO implementation principle
17, Java thread programming understand?
18. What is the data structure of HashMap, how is it implemented, is it thread-safe (no), and what are its thread-safe alternatives?
Interview questions and reference answers:
What challenges did you encounter in the project?
Reference: Worked on a high concurrency project for seckill.
1. What if traffic spikes at one point and then plummets?
Reference answer:
- Flow peak cutting and valley filling
- Queues messages on both the client and server as a caching mechanism
- The access layer and all modules use cache to increase QPS
2. How does redis message queue delete expired/invalid information
Reference answer:
- Add an expiration time upper limit
- Different queues are used for information in different groups. When the number of groups is full, the queues are deleted
3. Redis persistence mechanism?
- RDB and AOF
4. Why parent delegates are used for JAVA class loading
- Example: The Object class is unique
5. How to achieve synchronization
- The Synchronized keyword
- Volatile variables
- The Lock object
6. What types of JAVA locks are available
- Sychronized
- ReentrantLock
7. The difference between the two locks
- Synchronized is implemented by the JVM
- ReentrantLock is implemented by the JDK
6. Know about AQS?
- AQS (Abstract Queue Synchronizer) Queue Synchronizer
- It consists of a Valotaile variable marking State and a CLH (synchronization, FIFO) queue
Concrete implementation class:
- CountdownLatch: Waits for multiple threads to complete;
- CyclicBarrier: synchronization barrier;
- Semaphore: Controls the number of concurrent threads.
7. Scenario: Add a timeout exception to a method
- Use AspectJ for AOP development
- The method call is cut Around
- A Future object is used to create a thread that is timed while the method is called
- Throws a timeout exception if the Future returns a value first
- Otherwise, it is called normally
Corresponding interview questions to obtain answers: pay attention to the following public account can be obtained
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