Ace Your Java Backend Interview: From Self‑Intro to Redis Strategies and Design Patterns

In recent years, state‑owned enterprises have become a popular career choice for programmers, but the high competition raises the entry threshold, making interview opportunities scarce.

Are state‑owned enterprises truly "stable"? Stability is relative; future industry changes are unpredictable, so career trajectories remain uncertain.

Do they guarantee "leisure"? Many positions involve repetitive, process‑driven work that can be draining for developers seeking innovation.

Before applying, research the company online or directly ask current employees about the real work environment.

Simple Self‑Introduction

A concise self‑introduction (1‑2 minutes) should highlight your core tech stack (e.g., Java backend, distributed systems), showcase a key achievement with measurable impact, briefly mention 1‑2 relevant projects or competitions, and express genuine interest in the role.

State your main technology stack and expertise.

Emphasize strengths with a short example (e.g., solved a performance bottleneck, improving a metric by X%).

Briefly mention 1‑2 projects or achievements that align with the position.

If time permits, express enthusiasm for the role and the company.

Project Overview

When describing a project, consider the following structure:

Summarize the project in one sentence : explain the core business, goal, and pain point addressed.

Core features and highlights : focus on high‑value or technically challenging modules.

Architecture and technology selection : outline the overall architecture (micro‑services, monolith, middleware) and justify technology choices.

Clarify your role and contribution : specify your position (core developer, module lead, etc.) and responsibilities.

Key contributions : use the STAR method to present concrete cases with quantifiable results.

Problem‑solving highlights : describe the toughest technical challenge, your analysis, solution, and outcomes.

Deep dive into critical technologies : for example, discuss using Seata for distributed transactions and its configuration options.

Database Choices

I primarily use MySQL for persisting core business data due to its maturity, stability, and strong community support. To improve response speed and concurrency, Redis is introduced as a distributed cache for hot data, reducing MySQL pressure.

I have not yet used domestic databases directly, but I stay informed about their development.

Redis Expiration Strategies

Common expiration deletion strategies include:

Lazy deletion : keys are checked for expiration only when accessed.

Periodic deletion : a background task randomly samples keys with TTL and deletes expired ones.

Delay queue : keys are placed in a delayed queue and removed when the timer expires.

Timed deletion : each key sets a timer that triggers immediate deletion at expiration.

Redis combines periodic deletion and lazy deletion to balance CPU and memory usage.

Redis provides six main eviction policies:

volatile‑lru : evicts least‑recently‑used keys with an expiration.

volatile‑ttl : evicts keys that are about to expire.

volatile‑random : evicts random keys with an expiration.

allkeys‑lru : evicts least‑recently‑used keys among all keys.

allkeys‑random : evicts random keys among all keys.

no‑eviction : disables eviction; writes fail when memory is insufficient.

Since Redis 4.0, two LFU policies were added:

volatile‑lfu : evicts least‑frequently‑used keys with an expiration.

allkeys‑lfu : evicts least‑frequently‑used keys among all keys.

Design Patterns Used

Singleton : ensures a single instance for global resources such as configuration or connection pools.

Factory : abstracts object creation (simple factory, factory method, abstract factory).

Strategy : encapsulates interchangeable algorithms (e.g., different cloud storage implementations).

Observer : implements one‑to‑many dependency for event‑driven notifications.

Template Method : defines the skeleton of an algorithm while allowing subclasses to override specific steps.

When to Use Singleton

Use a singleton when a class must have exactly one instance throughout the application lifecycle and provide a global access point.

Heavy objects that are costly to create repeatedly (e.g., connection pools, thread pools).

Shared resources requiring consistent global state (e.g., configuration readers, counters).

Stateless utility classes (e.g., logger, ID generator).

Understanding Thread Safety

Thread‑safe : concurrent access by multiple threads does not compromise data correctness or consistency.

Thread‑unsafe : concurrent access may lead to data corruption, errors, or loss.

One‑Line Command to Kill All Java Processes

Linux/macOS:

ps -ef | grep '[j]ava' | awk '{print $2}' | xargs kill -9

ps -ef

: list all processes.

grep '[j]ava'

: filter processes containing "java".

awk '{print $2}'

: extract the PID column.

xargs kill -9

: force‑kill the listed PIDs.

A more concise alternative:

pkill -9 -f java

Windows:

taskkill /F /IM java.exe /T

taskkill

: terminates processes.

/F

: force termination.

/IM java.exe

: target processes named java.exe.

/T

: also terminate child processes.