Java

Java is a high-level, class-based, object-oriented programming language designed to be platform-independent through its "Write Once, Run Anywhere" philosophy.

Overview

Java runs on the Java Virtual Machine (JVM), which allows code to run on any device that has a JVM installed, regardless of the underlying architecture.

Pros

• Platform independence

• Strong ecosystem and libraries

• Excellent documentation

• Large community support

• Enterprise-grade security

• Automatic memory management

• Rich set of development tools

• Strong typing and compile-time checking

Cons

• Verbose syntax compared to modern languages

• Higher memory consumption

• Slower startup time compared to native applications

• Complex build systems for beginners

• Can be overly complex for simple tasks

Setup Guide

Linux (Ubuntu/Debian)

# Install OpenJDK
sudo apt update
sudo apt install openjdk-17-jdk

WSL

# Same as Linux installation
sudo apt update
sudo apt install openjdk-17-jdk

NixOS

# Add to configuration.nix
environment.systemPackages = with pkgs; [
  jdk17
  maven
  gradle
];

Development Tools

1. Build Tools:

   • Maven

   • Gradle

   • Ant (legacy)

2. IDEs:

   • IntelliJ IDEA

   • Eclipse

   • VS Code with Java extensions

Real-Life Example

Here's a simple Spring Boot REST API example:

// filepath: HelloWorldController.java
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.GetMapping;

@RestController
public class HelloWorldController {
    
    @GetMapping("/hello")
    public String hello() {
        return "Hello, DevOps World!";
    }
}

Project Structure Example

my-java-project/
├── src/
│   ├── main/
│   │   └── java/
│   │       └── com/
│   │           └── example/
│   │               └── Application.java
│   └── test/
│       └── java/
├── pom.xml
└── README.md

Maven Build File Example

// filepath: pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0">
    <modelVersion>4.0.0</modelVersion>
    
    <groupId>com.example</groupId>
    <artifactId>demo-project</artifactId>
    <version>1.0-SNAPSHOT</version>
    
    <properties>
        <java.version>17</java.version>
        <spring-boot.version>3.1.0</spring-boot.version>
    </properties>
</project>

Building and Running

Command Line Compilation

# Compile a single file
javac HelloWorld.java

# Run the compiled class
java HelloWorld

# Build with Maven
mvn clean install

# Run Spring Boot application
mvn spring-boot:run

Best Practices

1. Code Organization:

   • Follow package naming conventions

   • Use meaningful class and method names

   • Implement proper exception handling

2. Performance:

   • Use StringBuilder for string concatenation

   • Implement proper resource cleanup

   • Use collection frameworks appropriately

3. Testing:

   • Write unit tests using JUnit

   • Implement integration tests

   • Use mocking frameworks when needed

Common Tools for DevOps

1. Containerization:

FROM openjdk:17-slim
COPY target/*.jar app.jar
ENTRYPOINT ["java","-jar","/app.jar"]

1. CI/CD Pipeline Example (GitHub Actions):

name: Java CI
on: [push]
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-java@v2
        with:
          java-version: '17'
      - name: Build with Maven
        run: mvn clean install

Monitoring and Observability

• Use Spring Actuator for health checks

• Implement logging with SLF4J/Logback

• Use Prometheus and Grafana for metrics

• Implement distributed tracing with Jaeger or Zipkin

Remember to update the SUMMARY.md file to include this new Java guide in your wiki structure.