Java vs. C#

Data types	Java	C#
Single-root (unified) type system	No	Yes
Signed integers	Yes; 8, 16, 32, 64 bits	Yes; 8, 16, 32, 64 bits
Unsigned integers	No	Yes; 8, 16, 32, 64 bits
Character	Yes	Yes
Date/time	Yes; reference type	Yes; value type
IEEE 754 binary32 floating point number	Yes	Yes
IEEE 754 binary64 floating point number	Yes	Yes
High precision floating point number	No; but see Arbitrary size decimals	128-bit (28 digits) Decimal type
Boolean type	Yes	Yes
Strings	Immutable reference type, Unicode	Immutable reference type, Unicode
Arbitrary size integers	Reference type; no operators	Yes
Arbitrary size decimals	Reference type; no operators	No
Complex numbers	No	Yes
Reference types	Yes	Yes
Arrays	Yes	Yes
Value types	No; only primitive types	Yes
Enumerated types	Yes; reference type	Yes; scalar
Lifted (nullable) types	No; but wrapper types	Yes
Tuples	No	Yes
Pointers	No	Yes

Object orientation	Java	C#
Classes	Yes	Yes
Interfaces	Yes	Yes
Abstract classes	Yes	Yes
Member accessibility levels	Public, package, protected, private	Public, internal, protected, private
Class level inner classes	Yes	Yes
Instance level inner classes	Yes	No
Partial classes	No	Yes
Statement level anonymous classes	Yes	No
Implicit (inferred) anonymous classes	No	Yes
Deprecation/obsolescence	Yes	Yes
Overload versioning	Some	Yes
Properties	No, but see JavaBeans spec	Yes
Events	No; but the base class library does feature an event mechanism	Yes
Operator overloading	No	Yes
Indexers	No	Yes
Implicit conversions	No	Yes
Explicit conversions	No	Yes

Fields and initialization	Java	C#
Fields	Yes	Yes
Constants	Yes	Yes
Static (class) constructors	Yes	Yes
Instance constructors	Yes	Yes
Finalizers/destructors	Yes	Yes
Instance initializers	Yes	No
Object initialization	Bottom-up (fields and constructors)	Top-down (fields); bottom-up (constructors)
Object initializers	No	Yes
Collection initializers	No; can be modelled	Yes
Array initializers	Yes	Yes

Methods and properties	Java	C#
Static imports	Yes	No
Virtual	Virtual by default	Non-virtual by default
Abstract	Yes	Yes
Sealing	Yes	Yes
Explicit interface implementation	No	Yes
Value (input) parameters	Yes	Yes
Reference (input/output) parameters	No	Yes
Output (output) parameters	No	Yes
Variadic methods	Yes	Yes
Optional arguments	No	Yes
Named arguments	No	Yes
Generator methods	No	Yes
Extension methods	No	Yes
Conditional methods	No	Yes
Partial methods	No	Yes

Generics	Java	C#
Reified generics	No	Yes
Runtime realization	No	Yes
Covariance	Yes	Yes
Contravariance	Yes	Yes
Reference type constraint	Yes; implicit	Yes
Value/primitive type constraint	No	Yes
Constructor constraint	No	Yes
Relation constraint	Yes	Yes
Primitive/value type support	No	Yes
Migration compatibility	Yes	No

Functional programming	Java	C#
Method references	No; some use cases covered by anonymous inner classes	Yes
Closures/lambdas	No; some use cases covered by anonymous inner classes	Yes
Expression trees	No	Yes
Generic query language	No	Yes

Runtime (dynamic) binding	Java	C#
Late-bound (dynamic) type	No	Yes

Runtime type information and manipulation	Java	C#
Runtime type information	Yes; but with type erasure	Yes
Runtime generics realization	No	Yes
Runtime type construction	No; third party tools exist	Yes

Statements	Java	C#
Loops	Yes	Yes
Conditionals	Yes	Yes
Flow control	Yes	Yes
Assignment	Yes	Yes
Exception control	Yes	Yes
Variable declaration	Yes	Yes
Variable type inference	No	Yes
Deterministic disposal (ARM-blocks)	Yes (starting with Java 7)	Yes

Expressions and operators	Java	C#
Arithmetic operators	Yes	Yes
Logical operators	Yes	Yes
Bitwise logic operators	Yes	Yes
Conditional	Yes	Yes
String concatenation	Yes	Yes
Casts	Yes	Yes
Boxing	Yes; implicit	Yes; implicit
Unboxing	Yes; implicit	Yes; explicit
Lifted operators	No	Yes
Overflow control	No	Yes
Strict floating point evaluation	Yes; opt-in/out	No
Verbatim (here-)strings	No	Yes

Exceptions	Java	C#
Checked exceptions	Yes	No
Try-catch-finally	Yes	Yes

Arrays and Collections	Java	C#
Abstract data types	Yes	Partial
One-dimensional, zero-based index arrays	Yes	Yes
Rectangular (multidimensional) arrays	No	Yes
Jagged (arrays of arrays) arrays	Yes	Yes
Non-zero based arrays	No	Some
Unified arrays and collections	No	Yes
Maps/dictionaries	Yes	Yes
Sorted dictionaries	Yes	Yes
Sets	Yes	Yes
Sorted sets	Yes	Yes
Lists/vectors	Yes	Yes
Queues/stacks	Yes	Yes
Priority queue	Yes	No
Bags/multisets	Yes	Yes

Metadata	Java	C#
Metadata annotations/attributes	Interface based	Class based
Positional arguments	No; unless a single argument	Yes
Named arguments	Yes	Yes
Default values	At definition	Through initialization
Nested types	Yes	Yes
Specialization	No	Yes
Conditional metadata	No	Yes

Preprocessing, Compilation and Packaging	Java	C#
Namespaces	Packages	Namespaces
Packaging	Package	Assembly
Classes/assembly search path	Yes; ClassPath	No; /lib
File contents	Restricted	Free
Conditional compilation	No	Yes
Custom errors/warnings	No	Yes
Explicit regions	No	Yes

Threading and Synchronization	Java	C#
Threads	Yes	Yes
Thread pool	Yes	Yes
Task based parallelism	No	Yes
Semaphores	Yes	Yes
Monitors	Yes	Yes
Thread local variables	Yes	Yes; ThreadStaticAttribute

Native interoperability	Java	C#
External/native methods	Yes	Yes
Marshalling	External glue code required	Yes; metadata controlled
Pointers and arithmetics	No	Yes
Native types	No	Yes
Fixed size buffers	No	Yes
Explicit stack allocation	No	Yes
Address-of	No	Yes
Object pinning (fix variable to address)	No	Yes