C# vs Java

Methods
At the basic level there are no differences between C# and Java methods; each method takes parameters, and has a return type.

class A {

public void MethodA1() { }

public int MethodA2() { }

public void MethodA3( int i ) { }

public int MethodA4{ int i ) { }

}

This creates a class A that has one method named MethodA1 that does not take any parameters and does not return any value. MethodA2 returns an integer, MethodA3 takes an integer as a parameter.

However, C# can do things with methods that could not be done before with Java.

Method signature and params
When calling a method, the Java compiler checks that there is a method that matches its signature. For example, in Java, if there is a method defined as

public void methodCaller( int a, int b, int c );

then a call of that method

methodCaller( 3, 4, 5, 6 );

will generate a compiler error as the Java compiler cannot find a method named methodCaller that takes four ints. We cannot create a method signature that allows us to take a variable number of ints as parameters.

Why should this even matter? If a programmer wants to take a variable number of ints, he can define a method signature that takes an array of integers and then construct the array when calling the method. In Java, this will take at least three lines of code just to call the method the first to create the array, one or more lines to assign values into the array, and the third to call the method.

C# eases this issue by allowing programmers to place a params modifer on the last array parameter of the method, so that a variable number of parameters can be passed into it. Using the above example, the method signature can be defined as

public void methodCaller( params int[] a );

and the method can be called with any of

methodCaller( 1 );

methodCaller( 1, 2, 3, 4, 5 );

Inside methodCaller, the parameters can be accessed through the "a" array defined.

Passing by reference and out

C# can also force a parameter to be passed in by reference as opposed to being passed by value. Let's consider a primitive type,

public void increment( int a ) {

a++;

}

int a = 3;

increment( a );

// a still == 3

will not cause the variable passed into increment to actually be incremented because "a" is being passed in by value; the variable a in the increment block is in a different environment, and therefore changes in that scope do not propagate back out.

However, changing the method to

public void increment( ref int a ) {

a++;

}

int a = 3;

increment( ref a );

// a now == 4

will cause the int "a" to be passed in by reference (just as classes are passed in) and therefore modifying it will cause the original value to be changed. Using ref with a class allows a function to reassign the class pointer inside the function and have that change propagate outside the method.

A natural partner to ref is the out keyword. While ref does not guarantee that any operations will actually be performed on the variable, using out will cause the compiler to make sure that a value has been set to the variable. Code such as

public void DoNothing( out int a ) { }

will cause the compiler to complain as "a" is not assigned to anything.

Properties
Properties is a C# construct that formalizes the get/set pattern seen in many Java classes. The Java paradigm of having a get method that takes one parameter and a set method that returns the said parameter is compacted. So the following Java code:

private int name;

public int getName()

{

return this.name;

}

public void setName( int name )

{

this.name = name;

}

can be written in C# as

private int property;

public int Property {

get {

return this.property;

}

set {

// value is an implicit variable generated by the

// compiler to represent the parameter

this.property = value;

}

}

Behind the scenes, C# actually compiles the property to two methods in the .NET intermediate language framework named get_Property and set_Property. These methods cannot be called directly from C#, but other languages using the MSIL should be able to access these getters/setters.

Accessibility Modifiers
Access modifiers restrict the ability for only certain code to change a field. The ones that a Java programmer is used to are private, protected, default, and public.

C#, in turn, has five modifiers:

These modifiers can be applied to the same structures and modify the accessibility to objects, methods, and variables.

Source Files
In Java, each class needs to exist in a like-named file (with the like-named extension .java) there are exceptions with class visible and inner classes, as those are defined within another class's .java file.

C# does not have this or any restriction when it comes to defining classes, even when they are in different namespaces any part of a C# program may exist in the same .cs file, so as to form a self-contained unit.

File Naming Convention
C# follows mixed-caps style, except that method names typically also capitalize their first letter. It is also common to see that variables in the BCL (Base Class Library) have capital letters as the first character, although most user-defined variables are defined with a lowercase first letter.

There is no distinction made between the naming convention of constants and assignable variables, as both use mixed caps.

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