I was looking at a typical for loop:
class ForDemo {
public static void main(String[] args){
for(int i=1; i<11; i++){
System.out.println("Count is: " + i);
}
}
}
I am happy with the semicolons after int i=1: it is a statement which declares the new variable i. If i++ is also a statement, why doesn't it have a semicolon after?
Another example. I opened the Jshell and put the following:
jshell> int a=1;
a ==> 1
jshell> a++
$2 ==> 1
jshell> a
a ==> 2
jshell> int b=1;
b ==> 1
jshell> b++;
$5 ==> 1
jshell> b
b ==> 2
In other words the command ++ works, independently from whether there is a semicolon or not. I expected not to work without it.
Last example (adapted from a presentation about the difference between = and ==):
jshell> boolean x = false;
x ==> false
jshell> if (x = true) System.out.println("Sorry! This is wrong ...");
Sorry! This is wrong ...
jshell> boolean x = false;
x ==> false
jshell> if (x = true;) System.out.println("Sorry! This is wrong ...");
| Error:
| ')' expected
| if (x = true;) System.out.println("Sorry! This is wrong ...");
| ^
I get the point about the difference between = and ==. My question is why it works in the first half (if (x = true) without ;), and not with a ; (if (x = true;)).
Apologies for the several examples, but I think the question is relatively straightforward: if there are instances where an expression (without ;) works as a command statement (with ;), what is the function of semicolons?
The semiccolon is a separator of stack calls. The inside of if() wants a boolean, not a stack call. Only inside the {} are statements expected.
The inside of for() expects three stack calls: One defining the loop variable, one defining the breaking clause and one defining what happens after each loop.
Example: The construct for(;;); is a valid java construct. But you should never use it as the only thing it would do is loop over nothing forever: You don't define a variable, a breaking condition or something that gets executed after each call. During the loop you also just do nothing.
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