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Java

Posted by Stephen Blank
Stephen Blank
16,286 Points

For Loop Syntax

Can anyone explain what i --> 0 is doing? I don't understand the syntax.

public class Main { public static void main(String[] args) { int N = 77777777; long t;

    {
        StringBuffer sb = new StringBuffer();
        t = System.currentTimeMillis();
        for (int i = N; i --> 0 ;) {
            sb.append("");
        }
        System.out.println(System.currentTimeMillis() - t);
    }
}

}

1 Answer

andren
andren
28,558 Points
andren
andren
28,558 Points

You know how you can increase or decrease a variable by using ++ or --? That is what's being done here. It's just spaced in a confusing manner. There is a space between i and the --, and no space between the -- and the less than symbol, since Java doesn't really care all that much about how you space your code so long as you place the semicolon in the right place odd spacing like that is technically valid.

Changing the spacing like this:

for (int i = N; i-- > 0;) {
    sb.append("");
}

Makes it slightly clearer what is actually happening. In reality it's just a quicker (but harder to read) way of writing this:

for (int i = N; i > 0; i--) {
    sb.append("");
}

They essentially just merged the comparison of i and the subtraction of i into one step, which makes the code smaller. I would not recommend writing code in this style though as it will likely cause more confusion than benefit.