What are major differences between C# and Java?
I just want to clarify one thing. This is not a question on which one is better, that part I leave to someone else to discuss. I don't care about it. I've been asked this question on my job interview and I thought it might be useful to learn a bit more.
These are the ones I could come up with:
- Java is "platform independent". Well nowadays you could say there is the Mono project so C# could be considered too but I believe it is a bit exaggerating. Why? Well, when a new release of Java is done it is simultaneously available on all platforms it supports, on the other hand how many features of C# 3.0 are still missing in the Mono implementation? Or is it really CLR vs. JRE that we should compare here?
- Java doesn't support events and delegates. As far as I know.
- In Java all methods are virtual
- Development tools: I believe there isn't such a tool yet as Visual Studio. Especially if you've worked with team editions you'll know what I mean.
Please add others you think are relevant.
Update: Just popped up my mind, Java doesn't have something like custom attributes on classes, methods etc. Or does it?
Answer
Comparing Java 7 and C# 3
(Some features of Java 7 aren't mentioned here, but the using statement advantage of all versions of C# over Java 1-6 has been removed.)
Not all of your summary is correct:
- In Java methods are virtual by default but you can make them final. (In C# they're sealed by default, but you can make them virtual.)
- There are plenty of IDEs for Java, both free (e.g. Eclipse, Netbeans) and commercial (e.g. IntelliJ IDEA)
Beyond that (and what's in your summary already):
- Generics are completely different between the two; Java generics are just a compile-time "trick" (but a useful one at that). In C# and .NET generics are maintained at execution time too, and work for value types as well as reference types, keeping the appropriate efficiency (e.g. a
List<byte>as abyte[]backing it, rather than an array of boxed bytes.) - C# doesn't have checked exceptions
- Java doesn't allow the creation of user-defined value types
- Java doesn't have operator and conversion overloading
- Java doesn't have iterator blocks for simple implemetation of iterators
- Java doesn't have anything like LINQ
- Partly due to not having delegates, Java doesn't have anything quite like anonymous methods and lambda expressions. Anonymous inner classes usually fill these roles, but clunkily.
- Java doesn't have expression trees
- C# doesn't have anonymous inner classes
- C# doesn't have Java's inner classes at all, in fact - all nested classes in C# are like Java's static nested classes
- Java doesn't have static classes (which don't have any instance constructors, and can't be used for variables, parameters etc)
- Java doesn't have any equivalent to the C# 3.0 anonymous types
- Java doesn't have implicitly typed local variables
- Java doesn't have extension methods
- Java doesn't have object and collection initializer expressions
- The access modifiers are somewhat different - in Java there's (currently) no direct equivalent of an assembly, so no idea of "internal" visibility; in C# there's no equivalent to the "default" visibility in Java which takes account of namespace (and inheritance)
- The order of initialization in Java and C# is subtly different (C# executes variable initializers before the chained call to the base type's constructor)
- Java doesn't have properties as part of the language; they're a convention of get/set/is methods
- Java doesn't have the equivalent of "unsafe" code
- Interop is easier in C# (and .NET in general) than Java's JNI
- Java and C# have somewhat different ideas of enums. Java's are much more object-oriented.
- Java has no preprocessor directives (#define, #if etc in C#).
- Java has no equivalent of C#'s
refandoutfor passing parameters by reference - Java has no equivalent of partial types
- C# interfaces cannot declare fields
- Java has no unsigned integer types
- Java has no language support for a decimal type. (java.math.BigDecimal provides something like System.Decimal - with differences - but there's no language support)
- Java has no equivalent of nullable value types
- Boxing in Java uses predefined (but "normal") reference types with particular operations on them. Boxing in C# and .NET is a more transparent affair, with a reference type being created for boxing by the CLR for any value type.
This is not exhaustive, but it covers everything I can think of off-hand.