Java Cheat Sheet

Java cheat sheet with real commands and snippets for setup, core workflows, debugging, and production-safe automation patterns. If you are working across tools, pair this with the Maven Cheat Sheet and Gradle Cheat Sheet.

Setup and Tooling

Goal: Install and verify language toolchain

# Run java command
java --version

# Run javac command
javac --version

# Run mvn command
mvn -version

Core Workflows

Goal: Run and build source code

# Execute javac workflow
javac src/Main.java -d out

# Execute java workflow
java -cp out Main

Goal: Use a practical code snippet

public class Main {
  public static void main(String[] args) {
    System.out.println("Hello Java");
  }
}

Testing and Formatting

Goal: Run automated tests

# Execute test-related command
mvn test

# Execute test-related command
mvn -q test

Goal: Run lint and formatter checks

# Execute quality command
mvn spotless:apply

# Execute quality command
mvn checkstyle:check

Automation and CI

Goal: Create a repeatable CI shell step

# Run strict shell mode for CI step
set -euo pipefail

# Install dependencies deterministically
npm ci || pip install -r requirements.txt || true

# Run tests and fail fast on errors
mvn test

Debugging and Troubleshooting

Goal: Trace runtime issues

# Print runtime and package manager versions
node --version || python --version || true

# Search stack traces and TODO markers
rg "Traceback|Exception|TODO" .

# Re-run tests with verbose output
mvn test -v || mvn test --verbose || true

Common Gotchas

• Pin Java language/runtime versions in local and CI environments.
• Keep formatting and linting automated to avoid noisy diffs in code review.
• Prefer explicit dependency lock files for reproducible builds.
• Write small, deterministic tests that can run quickly in pre-commit checks.
• Document compiler/interpreter flags used in production builds.

Related Sheets

• Maven Cheat Sheet — daily Maven commands and production-ready examples.
• Gradle Cheat Sheet — daily Gradle commands and production-ready examples.
• Go Cheat Sheet — daily Go commands and production-ready examples.