A quick intro to iPhone development for Javans

A brief Java-oriented glossary
If you are coming from Java (the language, not the place), then here's a very brief Java-to-UIKit guide.  (Note: some of these are only approximately equal)

• interface (Java) = protocol (ObjC)
• static method = class method
• java.lang.Object = NSObject
  
• javax.swing.JOptionsPane = UIAlertSheet
• null = nil
• System.out.println("my object=" + myObject); = NSLog(@"my object=%@", myObject);
• "a literal string" = @"a literal string"
• java.lang.String = NSString
• boolean = BOOL
• java.util.ArrayList = NSMutableArray
• map = dictionary
• this = self
  

For loop
One thing that sort of bugs me is that you aren't allowed to do this: "for (int i=0; i<10; i++)"...you can't declare the variable 'i' there.  You have to do this instead:
int i;
for (i=0; i<10; i++)

Methods in ObjC
(Note: the word "method" will be used interchangeably with the words "function" and "procedure".)

The most obvious difference between Java and Objective C is probably the ways methods are declared. 

A regular ole method declaration looks like this:
- (int) getSomeNumber: (int) aParameter withAnotherParameter: (NSString*) aStringParameter
This would be equivalent to:
private int getSomeNumber(int aParameter, String aStringParameter)

• First, notice that it starts with a hypen (a minus sign).  If this were a plus sign (+), it would mean the function is a "class method" (known in Java as a static method).
• Next, notice that Objective C puts the variable type in parentheses, sort of like you do when you cast from one type to another.  The parentheses do not enclose the entire parameter list.
  
• Notice there are no commas...also note that ObjC uses labels for parameters (starting with the second one).  In the previous example, it is "withAnotherParameter".  This is just something that helps describe what the next variable is, and I could have just as easily used "fooMcLovin" or some other nonsense instead.
• The asterisk means that ObjC uses the same pointer notation as C/C++.

When you call the function, it will look something like this:
int x = [myObject getSomeNumber: 32 withAnotherParameter: @"some string I made up"];
(Technically, in ObjC, you aren't calling methods...you are sending messages, but we'll ignore this distinction for the time being.)


Other differences
There are many more differences that I'm not going to cover in this article...e.g. header files, pointers, memory management (no more garbage collection).  These will hopefully be addressed in some form or another in later articles.