C# vs Java: The Differences That Matter in Interviews

C# and Java share a common ancestor and a similar shape: both are garbage-collected, statically-typed, JVM/CLR-run languages with curly-brace syntax. But the differences are where interviews go. If you know one, the other is learnable in days — knowing the differences is the interview answer.

The one-line summary

Java is the conservative platform language with a massive ecosystem; C# is the feature-forward language that ships more conveniences faster. Both compile to bytecode, both have a mature standard library, both are GC'd. The differences below are the ones worth naming.

Value types and struct

C# has true value types:

struct Point { public int X, Y; }

A struct is copied by value and can live on the stack — no heap allocation, no GC pressure. Java has no user-defined value types (project Valhalla is in progress); all objects are heap-allocated references. The struct/record struct answer is a classic C#-interview differentiator.

Properties

C# has first-class properties:

public string Name { get; set; } = "";
public decimal Salary { get; private set; }

Java's answer is getters/setters — private String name; public String getName() {...}. C# bundles the accessors into property syntax, and can enforce readonly (get only), init-only, and computed values.

LINQ vs streams

C# has LINQ — query syntax and extension methods over IEnumerable<T>, with deferred execution:

var top = employees
    .Where(e => e.Salary > 80000)
    .OrderByDescending(e => e.Salary)
    .Select(e => e.Name);

Java has the Stream API (filter, map, sorted, collect), which is similar in spirit but verbose and different in details (parallel streams, no query syntax). Interviewers often ask the equivalent of one in terms of the other.

Delegates, events, and lambdas

C# has first-class delegates (Func<T>, Action<T>) and the event model built on them. Java has functional interfaces and lambdas, but events are idiomatic to C#. The "what's the difference between a delegate and an event" question has no Java equivalent.

Records

Both modern languages now have records:

public record Person(string Name, int Age);

public record Person(String name, int age) {}

Both give value equality and immutability by default. The C# twist: with expressions for non-destructive mutation, and record struct for value-type records. Java's records are the closer relative of C# records than of Java's old POJO boilerplate.

Nullable handling

Both have evolved: Java has Optional and now pattern matching; C# has nullable reference types (string?) enforced at compile time, plus the null-coalescing operator ?? and null-conditional ?.:

var name = person?.Name ?? "unknown";

Runtime differences

The real divide is ecosystem: Java is the default for enterprise/backend infrastructure; C# dominates Windows/.NET shops, Unity game dev, and Azure stacks. "Which would I pick?" answers are context, not religion.

The interview answer

"Both are GC'd, statically-typed languages with mature runtimes. C# moves faster on language features — value types with struct, properties, LINQ, delegates and events, and records with with expressions. Java leads on ecosystem reach and conservative stability. The right choice depends on the stack you're joining, not on one being 'better.'"

Related guides

• Top C# Interview Questions — LINQ, async/await, .NET GC
• Top Java Interview Questions — JVM memory, collections, concurrency