C++ – Why is it called ‘wchar_t’ and not simply ‘wchar’

The name reflection is used to describe code which is able to inspect other code in the same system (or itself).

For example, say you have an object of an unknown type in Java, and you would like to call a 'doSomething' method on it if one exists. Java's static typing system isn't really designed to support this unless the object conforms to a known interface, but using reflection, your code can look at the object and find out if it has a method called 'doSomething' and then call it if you want to.

So, to give you a code example of this in Java (imagine the object in question is foo) :

Method method = foo.getClass().getMethod("doSomething", null);
method.invoke(foo, null);

One very common use case in Java is the usage with annotations. JUnit 4, for example, will use reflection to look through your classes for methods tagged with the @Test annotation, and will then call them when running the unit test.

There are some good reflection examples to get you started at http://docs.oracle.com/javase/tutorial/reflect/index.html

And finally, yes, the concepts are pretty much similar in other statically typed languages which support reflection (like C#). In dynamically typed languages, the use case described above is less necessary (since the compiler will allow any method to be called on any object, failing at runtime if it does not exist), but the second case of looking for methods which are marked or work in a certain way is still common.

Update from a comment:

The ability to inspect the code in the system and see object types is not reflection, but rather Type Introspection. Reflection is then the ability to make modifications at runtime by making use of introspection. The distinction is necessary here as some languages support introspection, but do not support reflection. One such example is C++

The do ... while and if ... else are there to make it so that a semicolon after your macro always means the same thing. Let's say you had something like your second macro.

#define BAR(X) f(x); g(x)

Now if you were to use BAR(X); in an if ... else statement, where the bodies of the if statement were not wrapped in curly brackets, you'd get a bad surprise.

if (corge)
  BAR(corge);
else
  gralt();

The above code would expand into

if (corge)
  f(corge); g(corge);
else
  gralt();

which is syntactically incorrect, as the else is no longer associated with the if. It doesn't help to wrap things in curly braces within the macro, because a semicolon after the braces is syntactically incorrect.

if (corge)
  {f(corge); g(corge);};
else
  gralt();

There are two ways of fixing the problem. The first is to use a comma to sequence statements within the macro without robbing it of its ability to act like an expression.

#define BAR(X) f(X), g(X)

The above version of bar BAR expands the above code into what follows, which is syntactically correct.

if (corge)
  f(corge), g(corge);
else
  gralt();

This doesn't work if instead of f(X) you have a more complicated body of code that needs to go in its own block, say for example to declare local variables. In the most general case the solution is to use something like do ... while to cause the macro to be a single statement that takes a semicolon without confusion.

#define BAR(X) do { \
  int i = f(X); \
  if (i > 4) g(i); \
} while (0)

You don't have to use do ... while, you could cook up something with if ... else as well, although when if ... else expands inside of an if ... else it leads to a "dangling else", which could make an existing dangling else problem even harder to find, as in the following code.

if (corge)
  if (1) { f(corge); g(corge); } else;
else
  gralt();

The point is to use up the semicolon in contexts where a dangling semicolon is erroneous. Of course, it could (and probably should) be argued at this point that it would be better to declare BAR as an actual function, not a macro.

In summary, the do ... while is there to work around the shortcomings of the C preprocessor. When those C style guides tell you to lay off the C preprocessor, this is the kind of thing they're worried about.