Effective Java

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CHAPTER 9
GENERAL PROGRAMMING
264
Item 58: Prefer for-each loops to traditional 
for
 loops
As discussed in Item 45, some tasks are best accomplished with streams, others
with iteration. Here is a traditional 
for
loop to iterate over a collection:
// Not the best way to iterate over a collection!
for (Iterator i = c.iterator(); i.hasNext(); ) {
Element e = i.next();
... // Do something with e
}
and here is a traditional 
for
loop to iterate over an array:
// Not the best way to iterate over an array!
for (int i = 0; i < a.length; i++) {
... // Do something with a[i]
}
These idioms are better than 
while
loops (Item 57), but they aren’t perfect. The
iterator and the index variables are both just clutter—all you need are the elements.
Furthermore, they represent opportunities for error. The iterator occurs three times
in each loop and the index variable four, which gives you many chances to use the
wrong variable. If you do, there is no guarantee that the compiler will catch the
problem. Finally, the two loops are quite different, drawing unnecessary attention
to the type of the container and adding a (minor) hassle to changing that type.
The for-each loop (officially known as the “enhanced 
for
statement”) solves
all of these problems. It gets rid of the clutter and the opportunity for error by hid-
ing the iterator or index variable. The resulting idiom applies equally to collec-
tions and arrays, easing the process of switching the implementation type of a
container from one to the other: