Question

I’m new to Java. I’ve got 3 months experience of Objective-C so I understand its concepts quite easily. I am trying to port a simple factorial-example program written in Java to Objective-C for learning purposes. But there is this one line, I do not understand what is going on here:

for (int i; i < 10; i++){
println (i + "! =" + factorial(i));

Now the for loop and all that is fine, but this “! =” I´ve never seen — what does it do? To me it looks like a “not equal to” operator, wich would make no sense i + not equal too + factorial (factorial is a method, by the way).

Answer 1

This is building a string.

“+” in Java can be used to concatenate String. This happens if one of the parts is a String, and all other things are also converted to Strings (like the ints here).

The “!= ” is just a String literal, not anything that Java sees.

In Objective-C, it would be

 [NSString stringWithFormat:@"%d! = %d", i, factorial(i)]

Note that in Java, you can also do

 String.format("%d! = %d", i, factorial(i));

which may be more familiar to you.