for loop : Java Glossary

The for is Java’s multipurpose loop controller. It is most commonly used in this form:

for ( int i=0; i<n; i++ )
   {
   System.out.println(i);
   }

You can leave out any of the three sections of the

for ( init; should-I-continue-looping?; increment )

sections. If you leave out the should-I-continue-looping? boolean expression, it is assumed true. This means you can use a for to simulate while and do whileloops.

The other common use of for is to iterate over a collection like this:

for ( Iterator aIter = myCollection.iterator(); aIter.hasNext(); )
   {
   Thing item = (Thing) aIter.next();
   // do something with item
   }

Note the empty increment portion of the for. You have to do the next inside the loop body for iterators. for is preferable to using a while loop because the aIter variable is automatically made local to the loop.

For loops can have a dual index, like this:

for ( int i=0, j=n; i<n; i++,j-- )
   {
   /* loop body */
   }

or like this:

{
   int i,j;
   for ( i=0,j=n; i<n; i++,j-- )
      {
      /* loop body */
      }
}

{
   int i;
   float f;
   for ( i=0,f=n; i<n; i++,f*=.5 )
      {
      /* loop body */
      }
}

But, due to a hopelessly muddled for syntax dating back to C, (deriving from the attempt to reuse comma and semicolon in incompatible ways) you cannot write code like this:

for ( int i=0, float f=n; i<n; i++,f*=.5 )
   {
   /* loop body */
   }