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