Question

I wonder what is the best way to implement a “for-each” loop over an ArrayList or every kind of List.

Which of the followings implementations is the best and why? Or is there a best way?

Thank you for your help.

List values = new ArrayList();


values.add("one");
values.add("two");
values.add("three");
...

//#0

for(String value : values) {
    ...
}

//#1

for(int i = 0; i < values.size(); i++) {
    String value = values.get(i);
    ...
}

//#2

for(Iterator it = values.iterator(); it.hasNext(); ) {
    String value = it.next();
    ...
}

//#3

Iterator it = values.iterator();
while (it.hasNext()) {
    String value = (String) it.next();
    ...
}

Answer 1

#3 has a disadvantage because the scope of the iterator it extends beyond the end of the loop. The other solutions don’t have this problem.

#2 is exactly the same as #0, except #0 is more readable and less prone to error.

#1 is (probably) less efficient because it calls .size() every time through the loop.

#0 is usually best because:

• it is the shortest
• it is least prone to error
• it is idiomatic and easy for other people to read at a glance
• it is efficiently implemented by the compiler
• it does not pollute your method scope (outside the loop) with unnecessary names