Java

Write once, run anywhere

Java is a statically typed, object-oriented language that runs on the JVM. It powers Android, enterprise backends and big-data systems.

Android Apps

Enterprise Backends

Spring Boot APIs

Big Data (Kafka, Spark)

Time to learn: 3-4 months

1Hello World

beginner

Every Java app starts with a class containing a main method.

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

2Classes & Objects

beginner

Classes encapsulate data (fields) and behavior (methods).

public class User {
    private String name;
    private int age;

    public User(String name, int age) {
        this.name = name;
        this.age  = age;
    }

    public String greet() {
        return "Hi, I'm " + name;
    }
}

3Collections & Generics

intermediate

Lists, maps and sets backed by generics give you type-safe containers.

import java.util.*;

List<String> langs = new ArrayList<>();
langs.add("Java");
langs.add("Kotlin");

Map<String, Integer> scores = new HashMap<>();
scores.put("Ada", 95);

for (String l : langs) System.out.println(l);

4Streams & Lambdas

intermediate

Streams let you process collections in a declarative, functional style.

import java.util.*;
import java.util.stream.*;

List<Integer> nums = List.of(1, 2, 3, 4, 5);

int sum = nums.stream()
              .filter(n -> n % 2 == 0)
              .mapToInt(Integer::intValue)
              .sum();

System.out.println(sum); // 6

5Exception Handling

intermediate

try/catch/finally and try-with-resources keep code safe and resource-leak free.

try (var reader = new java.io.BufferedReader(new java.io.FileReader("data.txt"))) {
    String line;
    while ((line = reader.readLine()) != null) {
        System.out.println(line);
    }
} catch (java.io.IOException e) {
    e.printStackTrace();
}

Built something with Java?

Generate a professional README for your project in seconds.

Generate README Next: Learn C++