BAT Interview Guide: Java Advanced Topics, Algorithms, Performance Tuning, and High‑Concurrency Design

BAT Interview Questions (36 items) – Summary

BAT First Round: Java Advanced Topics

Which collection source codes have you read? (e.g., HashMap, Hashtable, ConcurrentHashMap, etc.)

Explain the initial capacity and expansion mechanism of ArrayList.

Describe the differences between ArrayList and LinkedList.

Why is insertion near the front of a LinkedList efficient, while insertion in the middle or tail of an ArrayList is faster?

Java JVM: memory model, generational layout, operations of each generation, and GC algorithms.

Class loaders, parent‑delegation model, custom delegation, and class isolation.

Implementation of HashMap and ConcurrentHashMap; why reads are lock‑free (use of volatile) and how long values are protected with segment locks.

How volatile works, lock categories, AQS overview, and fair vs. non‑fair locks.

Concurrency basics and the principle of ThreadLocal.

Differences between NIO and BIO.

Spring AOP and IoC concepts.

Algorithms

Improvements to bubble sort and quicksort.

Binary search and its variants.

Tree structures: binary tree, B+ tree, AVL tree, red‑black tree, Huffman tree.

Binary tree traversals (pre‑order, in‑order, post‑order) – recursive and non‑recursive implementations, plus level‑order traversal.

BAT Second Round: Performance Tuning & Caching

Java GC algorithms, garbage collectors, generational and region‑based tuning, and parameter configuration.

When do Minor GC and Full GC occur?

Common memory debugging tools: jmap, jstack, jconsole.

New features of Java 8.

Details of ConcurrentHashMap.

Redis data structures.

Redis threading model.

Redis eviction policies.

Have you read the Redis source code?

Four ACID properties of transactions.

MySQL transaction implementation principle (MVCC).

AOP transaction isolation levels and propagation characteristics.

Common HTTP request headers.

Why the TCP three‑way handshake involves three steps rather than two or four?

BAT Third Round: High‑Concurrency Project

How to implement a flash‑sale (秒杀) system? Core technologies and guarantees.

How to solve overselling? Discuss Spring transaction features.

Interview Summary

Strong fundamentals + solid project experience + good overall qualities increase the chance of receiving an offer.

If you have a solid foundation, sufficient project experience, and thorough preparation, your probability of getting an offer is high; otherwise, increase the number of applications and keep practicing.

Big companies like BAT value potential and are willing to invest in talent, so a strong foundation is essential. If you lack projects, focus on mastering fundamentals.

Fundamentals include programming language (C/C++ or Java), operating systems, TCP/IP, data structures & algorithms, and domain‑specific knowledge.

Project Experience Tips

Interviewers often ask:

What is your most technically challenging project and your role?

What was the biggest difficulty you faced, and how did you solve it?

Given a high‑concurrency scenario (e.g., flash sale), describe your design approach.

Good Overall Qualities

Good overall qualities mean proper etiquette, clear expression, and active communication during the interview. Companies also assess your personality, honesty, optimism, and humor, which can influence their decision.

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