C# vs Java: Syntax, Runtime, Generics, LINQ and Which to Learn

C# and Java are close relatives. Both are statically typed, object-oriented, garbage-collected languages with C-style syntax, both compile to bytecode for a virtual machine, and both are used for large backend systems. C# was released in 2002 partly as Microsoft's answer to Java, and over two decades the two have borrowed features from each other (lambdas, generics, records, pattern matching). A developer who knows one can read the other almost immediately.

The differences that matter day to day are smaller and more specific. This page goes through them with code: C# snippets you can run, Java in static blocks for comparison.

At a glance

Syntax: mostly the same

Classes, methods, if, for, while, switch, try/catch read almost identically. The visible differences are naming conventions and a few keywords: C# methods are PascalCase (ToUpper, WriteLine), Java methods camelCase (toUpperCase, println); C# writes string and bool, Java String and boolean; inheritance is class Dog : Animal in C# and class Dog extends Animal in Java.

// Java
import java.util.ArrayList;
import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<String> names = new ArrayList<>();
        names.add("Ana");
        names.add("Ben");
        for (String n : names) {
            System.out.println(n.toUpperCase());
        }
    }
}

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        var names = new List<string> { "Ana", "Ben" };
        foreach (string n in names)
        {
            Console.WriteLine(n.ToUpper());
        }
    }
}

Output:

ANA
BEN

C# also compares strings by value with ==, which removes one of Java's classic beginner bugs: in Java, == on two String objects compares references, so two equal strings built at run time (read from input, concatenated) can compare as unequal.

Properties instead of getters and setters

Java classes expose state through getName() and setName() methods, usually generated by an IDE or Lombok. C# has properties: members that read like fields but run code.

// Java
public class Product {
    private double price;
    public double getPrice() { return price; }
    public void setPrice(double price) {
        if (price < 0) throw new IllegalArgumentException("negative");
        this.price = price;
    }
}

using System;

class Product
{
    public string Name { get; set; }        // auto-property

    private decimal price;
    public decimal Price                     // property with validation
    {
        get { return price; }
        set
        {
            if (value < 0) throw new ArgumentException("Price cannot be negative");
            price = value;
        }
    }
}

class Program
{
    static void Main()
    {
        var p = new Product { Name = "Mug", Price = 8.50m };
        p.Price += 1.00m;                    // reads and writes like a field
        Console.WriteLine($"{p.Name}: {p.Price:F2}");
    }
}

Output:

Mug: 9.50

The object initializer new Product { Name = ..., Price = ... } sets properties right after construction. Java records (Java 16) cover the immutable-data case; C# has records too (C# 9), plus properties for everything else.

Value types: structs

In Java, every user-defined type is a reference type stored on the heap; only the eight primitives (int, double, ...) are values. C# lets you define your own value types with struct. A struct is copied on assignment and can live inline in arrays and other objects, with no separate heap allocation.

using System;

struct Point
{
    public int X;
    public int Y;
    public Point(int x, int y) { X = x; Y = y; }
}

class Program
{
    static void Main()
    {
        var a = new Point(1, 2);
        var b = a;          // copies the whole value
        b.X = 99;
        Console.WriteLine($"a = ({a.X}, {a.Y})");
        Console.WriteLine($"b = ({b.X}, {b.Y})");

        var grid = new Point[1000]; // one block of 1000 points, not 1000 objects
        Console.WriteLine(grid.Length);
    }
}

Output:

a = (1, 2)
b = (99, 2)
1000

This matters in games and numeric code, where millions of small objects would put pressure on the garbage collector. See structs.

Generics: reified vs erased

Java erases generic type arguments at compile time: at run time a List<Integer> is just a List, and List<int> is not allowed (you get boxed Integer objects). C# keeps the type arguments at run time, so List<int> stores raw ints and code can ask what T is.

using System;
using System.Collections.Generic;

class Program
{
    static string Describe<T>(List<T> items)
    {
        return $"{items.Count} items of type {typeof(T).Name}";
    }

    static T Create<T>() where T : new()
    {
        return new T();     // impossible in Java: T is erased
    }

    static void Main()
    {
        Console.WriteLine(Describe(new List<int> { 1, 2, 3 }));
        Console.WriteLine(Describe(new List<string> { "a" }));

        var list = Create<List<decimal>>();
        Console.WriteLine(list.GetType().Name);
    }
}

Output:

3 items of type Int32
1 items of type String
List`1

typeof(T) and new T() work because the runtime knows T. In Java both are compile errors, and the usual workaround is passing a Class<T> object around.

LINQ vs streams

Both languages have a fluent API for filtering and transforming collections. Java's is the Streams API (Java 8); C#'s is LINQ (C# 3), which also has a query syntax and works against databases through Entity Framework.

// Java
List<String> expensive = products.stream()
    .filter(p -> p.getPrice() > 20)
    .sorted(Comparator.comparing(Product::getPrice))
    .map(Product::getName)
    .collect(Collectors.toList());

using System;
using System.Linq;

class Program
{
    static void Main()
    {
        var products = new[]
        {
            new { Name = "Lamp", Price = 35m },
            new { Name = "Pen", Price = 2m },
            new { Name = "Chair", Price = 80m },
            new { Name = "Mug", Price = 9m }
        };

        var expensive = products
            .Where(p => p.Price > 20)
            .OrderBy(p => p.Price)
            .Select(p => p.Name)
            .ToList();
        Console.WriteLine(string.Join(", ", expensive));

        var total = products.Sum(p => p.Price);
        Console.WriteLine($"Total: {total}");
    }
}

Output:

Lamp, Chair
Total: 126

The operations map one to one (filter is Where, map is Select, collect(toList()) is ToList()), and the C# versions need no stream() or collector. The new { Name = ..., Price = ... } objects are anonymous types, which Java has no direct equivalent for.

Async and concurrency

C# introduced async/await in 2012: an async method returns a Task, and await suspends it without blocking a thread. JavaScript, Python and Rust later adopted the same keywords. Java took a different route: CompletableFuture chains, and since Java 21, virtual threads that make ordinary blocking code cheap.

// C#
async Task<string> LoadAsync(HttpClient http, string url)
{
    string body = await http.GetStringAsync(url);
    return body.Substring(0, 100);
}

// Java 21 with virtual threads: plain blocking code on a cheap thread
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
    executor.submit(() -> client.send(request, BodyHandlers.ofString()));
}

Both approaches scale to many concurrent requests. C# makes the asynchrony visible in method signatures; Java hides it in the runtime.

Exceptions, operators and smaller differences

• Checked exceptions. Java forces a method to declare or catch certain exceptions (throws IOException). C# has no checked exceptions at all.
• Operator overloading. C# lets types define +, ==, < and friends, which is why decimal and DateTime arithmetic reads naturally. Java does not (BigDecimal.add).
• Virtual by default. Java methods can be overridden unless marked final; C# methods must be marked virtual to be overridable, and the override must say override.
• Extension methods. C# can add methods to existing types ("text".IsPalindrome()); Java cannot.
• Nullable value types. int? in C# is an int that can be null; Java uses the boxed Integer.
• Unsigned types. C# has uint, ulong, ushort and an unsigned byte; Java's byte is signed, and apart from the 16-bit char it has no unsigned integer types.

Ecosystem, jobs and which to learn

Java's ecosystem is larger in the open source server world: Spring, Kafka, Spark, Hadoop, Elasticsearch and most Apache projects are Java. Android apps are written in Kotlin or Java. C# has the more integrated stack: one vendor maintains the language, runtime, web framework (ASP.NET Core), ORM (Entity Framework) and main IDE (Visual Studio), and Unity puts it at the center of game development.

Both languages have large job markets, and the balance between them depends on the region and the industry. C# is strong in companies built on Microsoft and Azure, in finance and healthcare software, and in game studios.

Pick C# if you want to make games in Unity, build Windows desktop apps, or work in a .NET company. Pick Java if you are aiming at Android, big data, or a company whose backend is on the JVM. Either one teaches the concepts you need for the other: classes, interfaces, generics, collections, exceptions and a garbage-collected runtime.