Difference between Java and c#

What is C# ?
 What do you guys think?
 C# a new programming language or a new version
of C/C++ ?
 It is a strong language for network and internet programming. C#
has redefined the programming landscape. In addition, C# designed
with the need of C/C++ and Java programmers. This new language
has been developed specifically with the .NET framework in mind,
and as such is designated to be the .NET developer's language of
choice. One very important matter about C#, it is the first component
oriented programming language.

Differences with JAVA!
1. Subtle Differences in terms of syntax of
Java and C#
2. Slight modification of concepts in C# that
already exist in Java
3. Language features and concepts that do not
exist in Java at all.

1. Differences in terms of Syntax:
Java main  C# Main
Java:
public static void main(String[] args)
C#:
static void Main(string[] args)
 string is shorthand for the System.String class in C#. Another
interesting point is that in C#, your Main method can actually be
declared to be parameter-less
static void Main()

Print statements
Java:
System.out.println("Hello world!");
C#:
System.Console.WriteLine("Hello world!");
or
Console.WriteLine("Hello again!");

Declaring Constants
Java:
 In Java, compile-time constant values are declared inside a class as
static final int K = 100;
C#:
 To declare constants in C# the const keyword is used for compile time
constants while the readonly keyword is used for runtime constants. The
semantics of constant primitives and object references in C# is the same as
in Java.
const int K = 100;

Inheritance
 C# uses C++ syntax for inheritance, both for class inheritance and interface
implementation as opposed to the extends and implements keywords.
Java:
class B extends A implements Comparable
{ ……………
……………
}
C#:
class B:A, IComparable
{ …………
…………
}

Primitive Types
 In Java, all integer primitive types (byte, short, int, long) are signed by
default.
 In C# there are both signed and unsigned varieties of these types:
Unsigned Signed Size
byte sbyte 8 bits
ushort short 16 bits
uint int 32 bits
ulong long 64 bits
 The only significantly different primitive in C# is the decimal type, a type
which stores decimal numbers without rounding errors. Eg:
decimal dec = 100.44m;

Array Declaration
 Java has two ways in which one can declare an array:
int[] iArray = new int[100]; //valid
float fArray[] = new float[100]; //valid
 C# uses only the latter array declaration syntax:
int[] iArray = new int[100]; //valid
float fArray[] = new float[100]; //ERROR: Won't compile

2. Modified concepts from Java:
Polymorphism & Overriding
 The means of implementing polymorphism typically involves having
methods in a base class that may be overridden by derived classes. These
methods can be invoked even though the client has a reference to a base
class type which points to an object of the derived class. Such methods are
bound at runtime instead of being bound during compilation and are typically
called virtual methods.
 In Java all methods are virtual methods while in C#, as in C++, one must
explicitly state which methods one wants to be virtual since by default they
are not.
 To mark a method as virtual in C#, one uses the virtual keyword. Also,
implementers of a child class can decide to either explicitly override the
virtual method by using the override keyword or explicitly choose not to
by using the new keyword instead

Polymorphism & Overriding
Example:
using System;
public class Parent
{ public virtual void DoStuff(string str)
{ Console.WriteLine("In Parent.DoStuff: " + str);
}
}
public class Child: Parent
{ public void DoStuff(int n)
{ Console.WriteLine("In Child.DoStuff: " + n);
}
public override void DoStuff(string str)
{ Console.WriteLine("In Child.DoStuff: " + str);
}
}
public new void DoStuff(string str)

Operator Overloading
 Operator overloading allows standard operators in a language to be
given new semantics when applied in the context of a particular class or
type.
 Operator overloading can be used to simplify the syntax of certain
operations especially when they are performed very often, such as
string concatenation in Java or interactions with iterators and collections
in the C++ Standard Template Library.
 Unlike C++, C# does not allow the overloading of the following
operators; new,( ), ||, &&, =, or any variations of compound
assignments such as +=, -=, etc.

Switch Statements
 There are two major differences between the switch statement in C# versus
that in Java.
 In C#, switch statements support the use of string literals and do not allow
fall-through unless the label contains no statements.
 switch(foo){
case "A": Console.WriteLine("A seen");
break;
case "B":
case "C": Console.WriteLine("B or C seen");
break;
/* ERROR: Won't compile due to fall-through at case "D" */
case "D": Console.WriteLine("D seen");
case "E": Console.WriteLine("E seen");
break;
}

Multiple Classes in a Single File
 Multiple classes can be defined in a single file in both languages
with some significant differences.
 In Java, there can only be one class per source file that has public
access and it must have the same name as the source file.
 C# does not have a restriction on the number of public classes that
can exist in a source file and neither is there a requirement for the
name of any of the classes in the file to match that of the source file.

Importing Libraries
 Both the langugaes support this functionality and C#
follows Java’s technique for importing libraries:
 C#: using keyword
using System;
using System.IO;
using System.Reflection;
 Java: import keyword
import java.util.*;
import java.io.*;

3. New Concepts in C#:
Enumerations
 Java's lack of enumerated types leads to the use of
integers in situations that do not guarantee type safety.
 C# code:
public enum Direction {North=1, East=2, West=4, South=8};
Usage:
Direction wall = Direction.North;
 Java equivalent code will be:
public class Direction {
public final static int NORTH = 1;
public final static int EAST = 2;
public final static int WEST = 3;
public final static int SOUTH = 4;
}
Usage:
int wall = Direction.NORTH;

Enumerations
 Despite the fact the Java version seems to express more, it doesn't,
and is less type-safe, by allowing you to accidentally assign wall to
any int value without the compiler complaining.
 C# enumerations support the ToString method, so they can
report their value as string (such as “North") and not just an an
integer.
 There also exists a static Parse method within the Enum class for
converting a string to an enumeration.

foreach Statement
 The foreach loop is an iteration construct that is popular in a number
of scripting languages (e.g. Perl, PHP, Tcl/Tk)
 The foreach loop is a less verbose way to iterate through arrays or
classes that implement the the System.Collections.IEnumerable
interface.
 Example:
string[] greek_alphabet = {"alpha", "beta", "gamma", "delta"};
foreach(string str in greek_alphabet) {
Console.WriteLine(str + " is a greek letter");
}

Properties
 Properties are a way to abstract away from directly accessing the
members of a class, similar to how accessors (getters) and
modifiers (setters) are used in Java.
 Particularly for read/write properties, C# provides a cleaner way of
handling this concept. The relationship between a get and set
method is inherent in C#, while has to be maintained in Java.
 It is possible to create, read-only, write-only or read-write properties
depending on if the getter and setter are implemented or not.

Properties
 Java:
public int getSize()
{ return size;
}
public void setSize (int val)
{ size = val;
}
 C#:
public int Size
{ get {return size;
}
set {size = val;
}
}

Pointers
 Although core C# is like Java in that there is no access to a pointer
type that is analogous to pointer types in C and C++, it is possible to
have pointer types if the C# code is executing in an unsafe context.
 Pointer arithmetic can be performed in C# within methods marked
with the unsafe keyword.
 Example:
public static unsafe void Swap(int* a, int*b)
{ int temp = *a;
*a = *b;
*b = temp;
}

Pass by Refernce
 In Java the arguments to a method are passed by value meaning
that a method operates on copies of the items passed to it instead of
on the actual items.
 In C#, it is possible to specify that the arguments to a method
actually be references.
 In Java trying to return multiple values from a method is not
supported.

The C# keywords used are ref and out.
ChangeMe(out s);
Swap(ref a, ref b);

REFERENCES:
 OOP with Microsoft VB.NET and Microsoft Visual C#.NET
by Robin A. Reyonlds-Haerle
 JAVA 2 Essentials
by Cay Horstmann
Websites:
 Java vs. C#: Code to Code Comparison
http://www.javacamp.org/javavscsharp/
 A Comparative Overview of C#:
http://genamics.com/developer/csharp_comparative.htm
 C#: A language alternative or just J--?,
http://www.javaworld.com/javaworld/jw-11-2000/jw-1122-csharp1.html
 A COMPARISON OF C# TO JAVA By Dare Obasanjo
http://www.soften.ktu.lt/~mockus/gmcsharp/csharp/c-sharp-vs-java.html#foreach
 Conversational C# for Java Programmers by Raffi Krikorian
http://www.ondotnet.com/pub/a/dotnet/2001/05/31/csharp_4_java.html

Difference between Java and c#

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