Comprehensive Java Interview Questions and Answers Overview

Java interview preparation often involves reviewing a large number of questions; the following list presents recent interview topics.

Java Basics

Object‑oriented features: inheritance, encapsulation, polymorphism.

Difference between int and Integer.

Integer value‑cache range.

Uses and implementation of reflection.

Differences between HTTP GET and POST requests.

MVC design concept.

What Java serialization and deserialization are.

How to implement Java serialization.

Difference between method overloading and overriding.

Processes and Threads

Concepts of thread and process.

Concepts of parallelism and concurrency.

Ways to create threads and their implementations.

Inter‑process communication methods.

Principles and differences of CountDownLatch and CyclicBarrier.

Principle of Semaphore.

Principle of Exchanger.

Analysis of ThreadLocal principle.

Why ThreadLocal can cause OOM and the deep reasons.

Implementation principles of thread pools.

Various thread‑pool implementation approaches.

Thread lifecycle and state transitions.

Lock Mechanism

What thread safety is and how to guarantee it.

Concept of re‑entrant lock and why it can prevent deadlock.

Four conditions that cause deadlock.

How to detect deadlock.

Implementation principle of volatile.

Implementation principle of synchronized (object monitor).

Differences between synchronized and Lock.

AQS synchronization queue.

CAS lock‑free concept; optimistic vs pessimistic lock.

Common atomic operation classes.

ABA problem and how JDK solves it.

Business scenarios and implementation of optimistic lock.

Common concurrency classes in Java 8’s java.util.concurrent package.

Concepts of biased lock, lightweight lock, heavyweight lock, and spin lock.

Database

Meanings of DDL, DML, DCL.

The EXPLAIN command.

Dirty read, phantom read, non‑repeatable read.

Transaction isolation levels.

Major database normal forms.

Sharding and partitioning design.

Distributed challenges caused by sharding/partitioning and corresponding solutions.

SQL optimization techniques.

Differences, advantages, disadvantages, and use cases of InnoDB vs MyISAM.

Differences among B+‑tree index, full‑text index, and hash index.

Adaptive hash index (AHI).

Why B+‑tree is used as MySQL’s index data structure.

Difference between clustered and non‑clustered indexes.

How to resolve slow loading when using LIMIT 20000.

Common distributed ID design schemes.

JVM

Division of JVM runtime memory areas.

Common garbage‑collection algorithms and their meanings.

Common JVM performance monitoring and troubleshooting tools.

JVM performance tuning techniques.

Class loader and parent‑delegation model.

Class‑loading process.

Strong, soft, weak, and phantom references.

Java Memory Model (JMM).

Answers are very detailed.

Source: https://dwz.cn/UFQmaazt