Java: What is "for (;;)"

Question

Would any one please explain this instruction for me: for (;;)

I have encountered several kinds of these mark (like in ajax code of facebook and in concurrent stuff of Java).

Answer 1

An infinite loop.

Each of the three parts of a for loop (for(x; y; z)) is optional.

So you can do this:

int i = 0;
for (; i < 20; ++i)

and it's perfectly valid, or

for (int i = 0; i < 20;) { ++i; }

or

for (int i = 0; ; ++i) { if (i < 20) { break; } }

and they're all valid.

You can also omit all three parts, with for(;;). Then you have a loop that:

• does no initialization (the first part)
• has no condition for stopping (the middle part)
• does nothing after each iteration (the last part)

so basically an endless loop. It just does what it says in the loop body, again and again

Answer 2

It's an endless loop. For the specificion of the for statement, see here.

Answer 3

That's an infinite loop, similar to

while(true)
{
    ...
}

Answer 4

Its an infinite loop, seeing as the (non-existent) exit condition will never be false.

Any for loop without an exit condition will be infinite:

for (int x=0; ; x++) { }

Exactly the same as while (true), although a little less readable IMHO.

Answer 5

That's indeed an infinite loop. But in Java you should really prefer while (true) over for (;;) since it's more readable (which you probably already realize). The compiler will optimize it anyway. In JavaScript there's no means of a compiler and every byte over HTTP counts, that's the reason why for (;;) is preferred. It saves a few characters (bytes).

Answer 6

The syntax for a for loop is

for (init-stmt; condition; next-stmt) {

}

So it is simply a for loop with no initial statement, next statement or condition. The absence of the exiting condition makes it infinite.