Java Code Review: Checklist, Best Practices & Review Tools

When left unchecked, a Java codebase can accumulate bugs, memory leaks, unhandled exceptions, and barely comprehensible code fragments. So, you need to perform Java code reviews to keep your application efficient, scalable, and secure. 

One problem, though, is that most teams loathe large-scale reviews. We believe that’s because they don’t follow a proper structure, and as a result, the process becomes unwieldy and overwhelming.

So, allow us to offer you a framework and some practices to make Java code review more manageable and efficient. We’ll also provide a detailed Java code review checklist, examples of widespread issues, and tools that streamline (and automate) various checks.

A Java code review is a systematic assessment of your source code to ensure it meets established standards and coding practices. It involves inspecting the code for errors, performance problems, security gaps, syntax issues, and documentation clarity.

In Java projects, regular code reviews have several purposes:

• Improved code quality: Reviews help adhere to uniform coding standards, naming conventions, and documentation style, resulting in efficient, error-free, and maintainable code.
• Performance enhancement: Addressing inefficient threads, memory-consuming objects, and collections helps improve application speed.
• Less waste: Code assessments provide an opportunity to mentor junior team members, reinforce best practices, and improve their skill levels. This ensures you make the most of your team and foster ongoing professional development to encourage long-term commitment to growing with the company.
• Increased code maintainability: Properly structured code leads to less technical debt and fewer unnecessary dependencies, making components more modular.
• Reduced vulnerabilities: Reviews help identify logical errors, memory leaks, unhandled exceptions, security flaws, and compliance issues.

Even experienced developers and testers tend to make mistakes or overlook certain practices. A comprehensive review can keep your codebase cleaner and easier to maintain.

A well-structured checklist helps teams enforce best practices, maintain code quality, and prevent common issues. To make the review easier, we describe how to review Java code by dividing it into different aspects of the codebase.

1. Code functionality and logic

At its core, code should function as intended, meet technical requirements, and handle expected inputs.

• Verify that the code performs the intended functions without altering unintended objects or variables.
• Ensure that requirements and user stories are accounted for, including edge cases (such as invalid inputs, boundary values, and unexpected data types).
• Confirm that data is passed correctly between components (without NullPointerExceptions, data format errors, etc.)
• Ensure the use of switch-case instead of multiple if-else statements to improve execution speed.

2. Readability and style

Java code should adhere to a project-wide style and be understandable to developers who didn’t write it.

• Check the naming conventions in Java (lowercase for packages, PascalCase for classes, camelCase for methods and variables, and UPPER_CASE for constants).
• Maintain standard formatting for indentation, brackets, and spacing.
• Ensure variable names are not shadowed and do not contain unnecessary syntax.
• Verify that commit messages describe what the change does and why it was made.

3. Structure and modularity

During a Java source code review, you should ensure the codebase is easy to modify, debug, and scale.

• Assess how well the codebase maintains separation of concerns (keeping logic in services instead of controllers).
• Verify if functions and classes are reusable across contexts.
• Identify common functionality and logic and see if it can be extracted into a shared parent class or method.
• Assess whether your Java collections are suitable for your use case, considering insertion, lookup, and concurrency requirements.
• Check for proper design patterns where applicable (Factory for conditions, Singleton for classes, and Observer for changes in multiple components).

4. Resource management

Resources should be properly allocated in Java applications to avoid memory leaks and crashes.

• Check if frequent values are grouped in ENUMs or stored as static constants (instead of magic numbers or hardcoded values).
• Validate that any rethrown exceptions preserve the original stack trace (so debugging retains the context).
• Check if data structures align with performance requirements (e.g., HashMap for fast lookups and ConcurrentHashMap for multi-threaded environments).
• Ensure JVM caches static final constants to reduce redundant calculations.
• Double-check resource closure (file handles, database connections) in a finally block or with try-with-resources to prevent leaks.
• Use WeakReferences or SoftReferences to allow objects to be garbage collected.
• Ensure that costly database queries are not repeatedly executed inside loops.
• Check for correct handling of hashCode() and equals() methods (a class must override both in hash-based collections).

5. Testing and coverage

A proper testing process reduces the number of bugs that slip into production, making it a critical part of the review.

• Check whether every feature goes through a set of unit tests in the CI/CD pipeline to validate its behavior.
• Verify that unit tests exist for new or changed functionalities, covering normal, edge case, and failure scenarios.
• Check code coverage stats to ensure tests sufficiently exercise core logic.

6. Error handling

A Java code review should validate whether errors and exceptions are properly logged, caught, and debugged.

• Check if relevant exceptions are always logged, wrapped, or rethrown (not swallowed silently).
• Assess whether the system checks for proper null validation and resource closure.
• Ensure that try-catch blocks include resource cleanup in a finally block.

7. Security

The security assessment should prevent data breaches, injection attacks, and critical system crashes. Ideally, it should be integrated at every stage of the project’s lifecycle, including regular Java code reviews.

• Ensure user input isn’t directly concatenated into SQL queries.
• Check that user-provided content isn’t rendered without sanitization to prevent Cross-Site Scripting (XSS).
• Ensure API keys, database credentials, and private tokens are not hardcoded into the source code.
• Check all authentication and authorization mechanisms, such as admin privileges and role-based access controls.
• Assess the system for outdated, vulnerable, or abandoned libraries.

8. Dependencies

Reviewing dependencies helps maintain an efficient Java application with compatible libraries.

• Confirm that the codebase doesn’t feature old or vulnerable dependencies.
• Determine if the codebase relies on proven frameworks (such as Spring, Apache Commons, or Logback).
• Check that custom implementations and utilities do not duplicate existing libraries.
• Validate that licensing requirements comply with the project’s policies.

9. Version control and build

A Java code review should include version control and build processes to ensure engineers work in coordination across environments.

• Check if the code follows a branching strategy (avoiding long-lived branches that diverge too far from main).
• Confirm that all build configuration settings were changed with a coherent reason. 
• Consider squashing multiple partial commits into a single commit to maintain a coherent history.
• Ensure that unused libraries or test dependencies are not included in production builds.

10. Documentation and comments

Review documentation in your code to ensure it helps developers understand functionalities and architecture.

• Ensure the documentation (README file) covers up-to-date project configuration, dependencies, APIs, and testing and deployment processes.
• Verify that the Java codebase includes high-level comments that clarify tricky logic or architectural decisions.
• Assess whether Javadoc comments for public APIs are clear and well-explained.
• Identify and remove unnecessary or commented-out code and debug print statements.

It’s crucial to identify and remediate all problems efficiently. Below are some Java code review examples of the practices you can follow.

Optimize string handling

Since String objects are immutable, every modification creates a new object in memory. To avoid unnecessary memory consumption, consider the following practices:

• Use StringBuilder (or StringBuffer) instead of plain String concatenation.
• Don’t overuse String.format() for simple concatenations.
• Avoid excessive logging with string concatenation inside log statements.

Maintain a logical package structure

A well-structured package hierarchy makes the codebase easier to modularize and maintain.

• Separate internal and public APIs to prevent unintended usage in unrelated modules.
• Use feature-based packaging instead of grouping by type.
• Keep package names short and meaningful to avoid deep nesting.

Follow OOP principles

Object-oriented programming (OOP) helps encapsulate your code, protecting object integrity and preventing unnecessary modifications.

• Keep fields and methods private, and use getter and setter methods when access outside the class is necessary.
• For objects that should not change after creation, mark fields as final and avoid exposing setters.
• Copy or wrap mutable collections before returning them to prevent external modification.

Utilize lambdas and streams

Lambdas and streams enable a declarative approach to data processing, replacing traditional imperative loops with concise and readable code.

• Leverage functional operations (filter, map, reduce) for simpler code instead of cumbersome loops.
• Avoid overusing streams in performance-critical loops where a clear, imperative style is preferable.

Implement interfaces

Interfaces are a powerful feature for decoupling implementations, but overusing them can lead to unnecessary complexity.

• Rely on interfaces rather than concrete classes to allow for easy implementation swaps in the future.
• Avoid “force-fitting” interfaces—introduce an interface only if multiple implementations are expected.
• Declare fields as List instead of locking your logic to a specific implementation like ArrayList, enabling future changes to LinkedList, if needed.

Structure exception handling with hierarchies

It’s good practice to define custom exception classes in larger Java applications during the review.

• Wrap third-party exceptions with custom messages for clarity.
• Catch exceptions from most specific to least specific (specialized exceptions before generic ones).
• Use checked exceptions for recoverable issues.

Foster a collaborative review process

The psychological aspect of the Java code review is critical yet often overlooked.

• Establish a code review team and define the assessment approach (over-the-shoulder review, pull requests, etc.).
• Treat code reviews as conversations, encouraging discussion about critical issues.
• Avoid overwhelming Java developers and testers with too many trivial comments.
• Integrate continuous Java code reviews in the CI/CD pipeline with automation tools.

With Java code review guidelines set, it’s worth talking about issues you may overlook and tools that can assist you.

Even the most experienced teams can overlook certain problems during the review, but being aware of potential pitfalls beforehand can make the process more effective.

Automation tools can help streamline the review and avoid many problems.

Reviews often blend automated tools, such as static analyzers or linting applications—with manual inspection. Here are some tools that can help improve the review process.

Static analysis
SonarQube, SpotBugs
Detects common Java bugs, concurrency and performance issues, code smells, and bytecode patterns.

Dependency checks
OWASP Dependency Check, Snyk
Scans Java projects for outdated or vulnerable libraries (against known CVEs) and identifies high-risk dependencies.

Formatting and style tools
Checkstyle, Google Java Format
Enforces project-wide styling rules and consistent code patterns and helps improve code readability.

Testing tools
JUnit, JaCoCo
Facilitates unit testing with clear assertions and lifecycle methods, measures code coverage, and highlights untested logic paths.

Documentation review
Swagger (OpenAPI), Enunciate
Generate interactive API docs or developer guides directly from annotations and code comments.

CI/CD automation
GitHub Actions, Jenkins
Automate builds, run tests, and gather static analysis results on new code commits.

Do you think you need help with reviewing your codebase? DevCom provides comprehensive source code review services to identify and address security, performance, and quality issues. 

We combine manual expertise with automated analysis and have certified expertise in Java (and other programming languages). Our engineers tackle complex tech stacks, guaranteeing that every line of code meets strict standards. Contact us to learn more about our review process.