The first thing that you’ll notice is that the two appear to be very similar syntactically and both lan-
guages are case-sensitive. C# is object-oriented like Java, and all functionality must be placed inside a
class (declared by the keyword
class). These classes can contain methods, constructors, and fields just
as Java classes can, and a C# class can inherit methods and fields from another class or interface as in
Java. The implementation of classes and methods is similar in both languages.
C# code blocks are enclosed by braces just as in Java. The entry point to a C# application is the static
Main() method, as required by the compiler (similar to Java but note the uppercase “M”). Also note that
only one class in the application can have a
Main() method. Similar to Java, the static keyword allows
for the method to be called without creating an instance of the class first. For the
Main() method in C#
you have the choice of either a
void or int return type. void specifies that the method does not return a
value and
int specifies that it returns an integer type.
The
using keyword in C# corresponds to the import keyword in Java. Therefore, in the C# code above,
we are essentially importing the C# equivalent of a class package called
System. In C#, a class package is
called a namespace, and we will look more closely at these in the next section.
Note that although we have written it with a lowercase s here, in C# the string type can also be written
with a capital S as String. You will also notice that the array rank specifier (
[]) has been shifted from in
front of the
args variable in the Java example, to between the string type and args variable in the C#
sample. In fact, this specifier can occur before or after the variable in Java. However, in C#, the array
rank specifier must appear before the variable name because an array is actually a type of its own indi-
cated by type
[]. We’ll discuss arrays in more depth a bit later.
Finally, as you might expect, the names of methods tend to differ between the languages. For example,
in Java we would use
System.out.println() to display text in the command console. The equivalent
to this method in C# is
System.Console.WriteLine().
Compiling and Running C# Code
In Chapter 2, we noted that like Java code, C# source code is compiled in two stages: first to
Intermediate Language (IL), and then to native code. To run the previous C# code, you need to save it
with an appropriate filename (for example, HelloWorld) and file extension .cs, and then compile it to IL
using the csc command:
csc HelloWorld.cs
The next step is to compile the IL to native code and run the example. To do this, just type the name of
the file, without the extension (as we would with Java code):
HelloWorld
Hello world! This is C# code!
Namespaces
While Java classes reside in logical divisions referred to as packages, C# (and other managed) classes are
grouped together into namespaces. Packages and namespaces differ significantly in their implementation.
A Java class that you want to make part of the
com.samples package, for example, must have package
com.samples; as the first line of code in the file. This is, of course, excluding any comments. Any code
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