C# for-java-developers

C# for Java Developers

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A Broad Overview

.NET Platform JVM Platform

IL Intermediate

LanguageBytecode

C# F# VB.NET Java Groovy Scala

CLR(Common Language Runtime)

Win Win Mac UnixLinux

csc javacgroovyc

fscvbc

scalac

JRE(Java Runtime Environment)

Mono

Technology StackJava C#

Data Access

Client Side GUI

Web Side GUI

Web Scripting

Web Hosting

Remote Invocation

Messaging

Native

Directory Access

Componentization

JDBC ADO.NET

AWT/Swing WinForms, WPF

JSP, JavaFX, JSF ASP.NET, WebForms

Servlets, Filters ISAPI, HttpHandler, HttpModule

Tomcat, Jetty, Weblogic etc... IIS

RMI, Netty, AKKA Remoting, now part of WCF

JMS, AKKA MSMQ

JNI PInvoke

JNDI Active Directory (Ldap/ADSI)

EJB (Entity/Session), Spring COM+, Managed Extensibility Framework (MEF)

Language ComparisonJava C#

Program Entry Point

Namespace

Including Classes

Inheritance

Overriding

Accessing Parent Ctor

Accessing Parent Method

Visibility

main(String ...args) Main() or Main(string [] args)

package namespace

import using

class (extends),interface (implements) class and interface (:)

virtual by default non-virtual by defaultuse virtual keyword

super(...) : base(...)

super.method(...) base.Method(...)

private, package, protected, public

private, protected, internal, internal protected, public


Abstract Class

Non-Extensible Class

Non-Writable Field

Non-Extensible Method

Constant

Checking Instance Type

Enums

for-each construct

Switch-Case

abstract class X { ... } abstract class X { ... }

final class X { ... } sealed class X { ... }

final readonly

final sealed

static final const

instanceof is

enum, can have fields, methods and implement interfaces and are typesafe

enum, cannot have methods, fields or implement

interfaces, not typesafe

for (item : collection) { ... }

foreach(item in collection) { ... }

numeric types (int, float...) enums, and now

strings (in Java 7)

numeric types, enums and strings


Method Parameters

Variable Arguments

Exceptions

ADT Meta Type

Meta Information

Static class

Properties

Non-Deterministic Object Cleanup

Object References are passed by Value only

Object reference are passed by Value(default), ref & out

method(type... args) Method(params type[] args)

Checked and Unchecked(enforced by javac, not by JIT

compiler)All Unchecked Exceptions

ClassClass klass = X.class;

TypeType type = typeof(X);

@Annotation [Attribute]

Simulated by private Ctor and static methods

Static class and ctor with static methods

getProperty(), setProperty()

Property { get; set; }compiler generated get_Property() and

set_Property() methods

finalize() destructor ~X()


Deterministic Object Cleanup

Generics

Class Loading

synchronized block

synchronized method

Thread Local Storage

Smallest Deployment Unit

Signing

AutoCloseable or Closeable try-with-resources (Java 7)

try ( ... ) { ... }

IDisposableusing ( ... ) { ... }

<T>, <T extends Type>, <?>Type Erasure

<T>, where T : type, new()Preserves Type Info

Class.forName(“fqn”)ClassLoader.getResources()

Activator.CreateInstance<T>()Assembly.Load()

synchronized (this) { ... } lock (this) { ... }

synchronized method() { ... }

[MethodImpl(MethodImplOptions.Synchronized)]void Method() { ... }

Thread relative static fields Thread relative static fields [ThreadStatic] and Data Slots

Jar EXE/DLLPrivate Assembly, Shared Assembly

Jar Signing Assembly Signing

Specific to C#

• Aliases

• Verbatim Strings

• var

• Partial Class/Method

• Object Initializer

• Named Args

• Optional Args

• Value Types(struct)

• Nullable Types

• Safe Cast

• Tuples

• Extension Methods

• Operator Overloading

• Indexer

Value Typeor

Ref Type?

Value Type use ==

Reference Type use ReferenceEquals

Specific to C#: Equality

• For Value Types, default Equals implementation uses reflection on fields.

• Override Equals for Reference Types

• Use the same strategy for Value Types, it is more performant and consistent as well.

Equality Similarities

• Define Equals(object other) and hashCode as a part of the contract

• Define both in terms of immutable fields

• It should be

• Reflexive: x.Equals(x) => True

• Symmetric: if x.Equals(y) then y.Equals(x) => True

• Transitive: x.Equals(y) and y.Equals(z), then x.Equals(z) =>

True

Specific to C#: Equality

• Use Exact object argument - Equals for use in Collections and for performance.

• IEquatable<T>

• Preserve Value Semantics for Value Types

• Overload == operator

Implicit & Explicit Interfaces

01. interface Greet1 {02. public String greet();03. }04.05. interface Greet2 {06. public String greet();07. }08. 09. public class Greeter implements Greet1, Greet2 {10. //Implicit Implementation11. public String greet() {12. {13. return “Hello”;14. }15.16. public static void main(String ...args) {17. Greet1 greeter1 = new Greeter();18. greeter1.greet(); // Hello19. 20. Greet2 greeter2 = new Greeter();21. greeter2.greet(); // Hello22.23. Greeter greeter = new Greeter();24. greeter.greet(); // Hello25. }26. }



Java: Implicit means whether you use Greet1 or Greet2, it invokes the same implementation.




01. interface Greet102. {03. string Greet();04. }05. interface Greet206. {07. string Greet();08. }09. public class Greeter : Greet1, Greet210. {11. //Implicit Implementation12. public string Greet() //Note the Visibility here13. {14. return “Hello”;15. }16.17. public static void Main()18. {19. Greet1 greeter1 = new Greeter();20. greeter1.Greet(); // Hello21. Greet2 greeter2 = new Greeter();22. greeter2.Greet(); // Hello23. Greeter greeter = new Greeter();24. greeter.Greet(); // Hello25. }26. }




01. interface Greet102. {03. string Greet();04. }05. interface Greet206. {07. string Greet();08. }09. public class Greeter : Greet1, Greet210. {11. //Implicit Implementation12. public string Greet() //Note the Visibility here13. {14. return “Hello”;15. }16.17. public static void Main()18. {19. Greet1 greeter1 = new Greeter();20. greeter1.Greet(); // Hello21. Greet2 greeter2 = new Greeter();22. greeter2.Greet(); // Hello23. Greeter greeter = new Greeter();24. greeter.Greet(); // Hello25. }26. }

C#: Implicit interface implementation

Specific to C#: Explicit Interfaces


01. interface Greet1 // v1.002. {03. string Greet();04. }05. interface Greet2 //v2.006. {07. string Greet();08. }09. public class Greeter : Greet1, Greet210. {11. //Explicit Implementations12. string Greet1.Greet() //Note the Visibility here13. {14. return “Hello from 1”;15. }16. string Greet2.Greet() //public not allowed for explicit17. {18. return “Hello from 2”;19. }20. public static void Main()21. {22. Greet1 greeter1 = new Greeter();23. greeter1.Greet(); // Hello from 124. Greet2 greeter2 = new Greeter();25. greeter2.Greet(); // Hello from 226. Greeter greeter = new Greeter();27. greeter. // No Greeters to Greet unless I cast28. }29. }


01. interface Greet1 // v1.002. {03. string Greet();04. }05. interface Greet2 : Greet1 // v2.006. {07. new string Greet();08. }09. public class Greeter : Greet210. {11. //Explicit Implementations12. string Greet1.Greet() //Note the Visibility here 13. {14. return “Hello from 1”;15. }16. string Greet2.Greet() //public not allowed for explicit17. {18. return “Hello from 2”;19. }20. public static void Main()21. {22. Greet1 greeter1 = new Greeter();23. greeter1.Greet(); // Hello from 124. Greet2 greeter2 = new Greeter();25. greeter2.Greet(); // Hello from 226. Greeter greeter = new Greeter();27. greeter. // No Greeters to Greet unless I cast28. }29. }



01. interface Greet1 // v1.002. {03. string Greet();04. }05. interface Greet2 : Greet1 // v2.006. {07. new string Greet();08. }09. public class Greeter : Greet210. {11. //Explicit Implementations12. string Greet1.Greet() //Note the Visibility here 13. {14. return “Hello from 1”;15. }16. string Greet2.Greet() //public not allowed for explicit17. {18. return “Hello from 2”;19. }20. public static void Main()21. {22. Greet1 greeter1 = new Greeter();23. greeter1.Greet(); // Hello from 124. Greet2 greeter2 = new Greeter();25. greeter2.Greet(); // Hello from 226. Greeter greeter = new Greeter();27. greeter. // No Greeters to Greet unless I cast28. }29. }


Explicitly State the interface for which the implementation is

Similarities• Immutable Strings

• Serialization

• Boxing

• Convert Value Type to a Reference Type

• Unboxing

• Convert Reference Type to a Value Type

Similarities

• Collections

• C# - IList, IDictionary, Queue, Stack

• Java - List, Map, Queue, Stack

• for-each Collection Iterators

Specific to C#• Collection Initializer

• Coroutines (more precisely Generators)

• yield break

• yield return

01. public static void Main() {02. foreach(int fiboSeq in new Fibonacci(5)) {03. Console.Out.WriteLine("{0}", fiboSeq);04. }05. }

Output:011235

Specific to C#• Collection Initializer

• Coroutines (more precisely Generators)

• yield break

• yield return

01. class Fibonacci : IEnumerable<int> {02. private readonly int howMany;03. private int firstSeed, secondSeed = 1;04.05. public Fibonacci(int howMany)06. {07. this.howMany = howMany;08. }09.10. public IEnumerator<int> GetEnumerator()11. {12. if (howMany < 0) 13. {14. yield break;15. }16. for (var i = 0; i <= howMany; i++)17. {18. yield return firstSeed;19. var sum = firstSeed + secondSeed;20. firstSeed = secondSeed;21. secondSeed = sum;22. }23. }24.25. IEnumerator IEnumerable.GetEnumerator()26. {27. return GetEnumerator();28. }29. }

01. public static void Main() {02. foreach(int fiboSeq in new Fibonacci(5)) {03. Console.Out.WriteLine("{0}", fiboSeq);04. }05. }

Output:011235

Covariance & Contravariance

• Covariance

• Pass collection of sub-class to a collection of base class

• Contravariance

• Pass collection of base class to a collection of sub-class

• Invariance

• Neither of the above applies

Arrays and Generic Collections

• Arrays are Covariant in C# and Java

• There is a hole in the type system and a runtime patch is applied.

• Generics are Invariant in Java.

• In C#, use leniency offered by IEnumerable if you need Covariance.

• Only interfaces and delegates can be covariant (out) or contravariant (in)

C# Example

C# Example01. abstract class Animal {02. public abstract string Speak();03. }04. 05. class Cat : Animal {06. public string Speak() {07. return “Meow!”;08. }09. }10. 11. class Dog : Animal {12. public string Speak() { 13. return “Bark!”;14. }15. }16.17. class Printer {18. public static Print(Animal [] animals) {19. animals[0] = new Dog();20. for (var i = 0; i < animals.Length; i++) {21. System.out.println(animals[i].speak();22. }23. } 24. 25. public static Print(IList<Animal> animals) {26. for (var animal in animals) {27. System.out.println(animal.Speak());28. }29. }30.

C# Example01. abstract class Animal {02. public abstract string Speak();03. }04. 05. class Cat : Animal {06. public string Speak() {07. return “Meow!”;08. }09. }10. 11. class Dog : Animal {12. public string Speak() { 13. return “Bark!”;14. }15. }16.17. class Printer {18. public static Print(Animal [] animals) {19. animals[0] = new Dog();20. for (var i = 0; i < animals.Length; i++) {21. System.out.println(animals[i].speak();22. }23. } 24. 25. public static Print(IList<Animal> animals) {26. for (var animal in animals) {27. System.out.println(animal.Speak());28. }29. }30.

01. public static Print(IEnumerable<Animal> animals)02. {03. for (var animal in animals) {04. Console.Out.WriteLine(animal.Speak());05. }06. }07. }08. class TestCollections {09. public static void main(String []args) {10. Cat cat = new Cat();11. Animal animal = cat;12. animal.speak();13. 14. animal = new Dog();15. animal.speak();16.17. Animal [] animals = new Animal [] { cat, dog }; 18. Cat [] cats = new Cat[] { cat };19. animals = cats;20. Print(animals); //Exposes Hole in Type System 21. 22. // In absence of above Print method, the code23. // does not compile as Generic Collections in24. // C# are Invariant. 25. List<Animal> animals = new ArrayList<Dog>();2627. //We need Co-variance to allow this to compile28. Printer.Print(dogs); 29. 30. }31. }

Java Example

Java Example01. abstract class Animal {02. public abstract String speak();03. }04. 05. class Cat extends Animal {06. public String speak() {07. return “Meow!”;08. }09. }10. 11. class Dog extends Animal {12. public String speak() { 13. return “Bark!”;14. }15. }16.17. class Printer {18. public static print(Animal [] animals) {19. animals[0] = new Dog();20. for (int i = 0; i < animals.length; i++) {21. System.out.println(animals[i].speak();22. }23. } 24. 25. public static print(List<Animal> animals) {26. for(Animal animal : animals) {27. System.out.println(animal.speak());28. }29. }30. }

Java Example01. class TestCollections {02. public static void main(String []args) {03. Cat cat = new Cat();04. Animal animal = cat;05. animal.speak();06. 07. animal = new Dog();08. animal.speak();09.10. Animal [] animals = new Animal [] { cat, dog }; 11. Cat [] cats = new Cat[] { cat };12. animals = cats;13. print(animals); //Exposes Hole in Type System 14. 15. // Fails to compile as Generic Collections in16. // Java are Invariant17. List<Animal> animals = new ArrayList<Dog>();18. 19. List<Dog> dogs = new ArrayList<Dog>();20. dogs.add(dog);21. dogs.add(dog);22. print(dogs);23. }24. }

01. abstract class Animal {02. public abstract String speak();03. }04. 05. class Cat extends Animal {06. public String speak() {07. return “Meow!”;08. }09. }10. 11. class Dog extends Animal {12. public String speak() { 13. return “Bark!”;14. }15. }16.17. class Printer {18. public static print(Animal [] animals) {19. animals[0] = new Dog();20. for (int i = 0; i < animals.length; i++) {21. System.out.println(animals[i].speak();22. }23. } 24. 25. public static print(List<Animal> animals) {26. for(Animal animal : animals) {27. System.out.println(animal.speak());28. }29. }30. }

Specific to C#• Anonymous Types

• Anonymous Methods/Delegates

• Pass Methods as Data

• Action: No return values

• Func: Non-void return values

• Predicate: A Func that always returns a bool

• Generally above suffice, but if not,then use Custom Delegates

• Delegate Chaining

• Compiler Eye Candy: +=, -= for Combine(), Remove()

• Lambdas

Specific to C#• Events

• Syntactic sugar over delegates, but with visibility

• Events can only be invoked from within the class that declared it, whereas a delegate field can be invoked by whoever has access to it.

• Events can be included in interfaces, delegates cannot be.

• Built-in EventHandler and EventArgs

• Compiler generated add_ and remove_ methods for the event.

• dynamic

• ExpandoObject

Dynamic Runtime Library

CLR(Common Language Runtime)

DLR(Dynamic Language Runtime)

C#

VB.NET

PythonRuby

• Allows you to talk with implementations in other languages

• C#/VB.NET with Python, Ruby

• Also with Silverlight etc..

Dynamically Typed

Statically Typed

01. using IronPython.Hosting;02. using Microsoft.Scripting.Hosting;03.04. var python = Python.CreateRuntime();05. dynamic script = python.UseFile(“Calculator.py”);06.07. // Get PythonType08. dynamic Calculator = script.GetVariable(“Calculator”);09. dynamic calc = Calculator(); // Instantiate Object10. 11. //Invoke method12. dynamic result = calc.add(2, 3); // 5

Specific to C#

• Avoid Configuration hell

• Single Configuration File (App.config)

• Asynchronous Programming

• BeginInvoke and EndInvoke• Wait with EndInvoke

• Wait with WaitHandle

• Poll for Async call completion

• Execute a callback upon completion

• Task Parallel Library (TPL)

Specific to Java

• Static Imports

• Instance and Static Initializers

• Interfaces Containing Fields

• Anonymous Classes

• Proxy Support through Interceptor

Specific to Java

• Asynchronous Programming

• Future Task

• Poll Completion with isDone().

• Execute callback upon completion

• Using ListenableFuture and FutureCallback - Google Guava Library

• Or roll your own result completion callback.

• Akka Actors

Frameworks and ToolsJava C#

Dependency Injection Frameworks

ORM Frameworks

Proxying/AOP Frameworks

TDD Frameworks

Mocking Frameworks

BDD Frameworks

Build Tools

Coverage Tools

Profiler

Code Analysis Tools

Spring, Guice, Pico Container etc... Spring.NET, Unity Container

Hibernate, iBatis etc... NHibernate, Entity Framework

JDK Proxy, Spring AOP, CGLib AspectJ, AspectWerkz

Castle Proxy, Rhino Proxy, Unity Interceptor

JUnit, TestNG NUnit, MSTest

JMock2, Mockito, EasyMock Rhino Mocks, Moq, TypeMock

Cucumber, JBehave, Spock, Easyb NBehave, SpecFlow, NSpec

Ant, Maven, Gradle, Ivy NAnt, MSBuild, NMaven

Cobertura, Emma, Clover NCover, OpenCover

JProfiler, YourKit dotTrace, YourKit.NET

FindBugs, PMD, Checkstyle, JDepend

FxCop, NDepend, ReSharper, Simian

References

• MSDN Site

• Venkat Subramaniam

• http://agiledeveloper.com/presentations/CSharpForJavaProgrammers.zip

• Wikipedia

• http://en.wikipedia.org/wiki/Comparison_of_C_Sharp_and_Java

• Dare Obasanjo

• http://www.25hoursaday.com/CsharpVsJava.html

• Scott Hanselman

• http://www.hanselman.com/blog/

C4AndTheDynamicKeywordWhirlwindTourAroundNET4AndVisualStudio2010Beta1.aspx

http://agiledeveloper.com/presentations/CSharpForJavaProgrammers.zip

http://agiledeveloper.com/presentations/CSharpForJavaProgrammers.zip

http://en.wikipedia.org/wiki/Comparison_of_C_Sharp_and_Java

http://en.wikipedia.org/wiki/Comparison_of_C_Sharp_and_Java

http://www.25hoursaday.com/CsharpVsJava.html

http://www.25hoursaday.com/CsharpVsJava.html

http://www.hanselman.com/blog/C4AndTheDynamicKeywordWhirlwindTourAroundNET4AndVisualStudio2010Beta1.aspx


