kooyee ‘s blog

Java 5 之后終于能在java中使用for each 循環

for (type var : arr) {
    body-of-loop
}

for (int i = 0; i < arr.length; i++) { 
    type var = arr[i];
    body-of-loop
}

For-each loop	Equivalent for loop
for (type var : arr) { body-of-loop }	for (int i = 0; i < arr.length; i++) { type var = arr[i]; body-of-loop }
for (type var : coll) { body-of-loop }	for (Iterator<type> iter = coll.iterator(); iter.hasNext(); ) { type var = iter.next(); body-of-loop }

Where the for-each is appropriate

Altho the enhanced for loop can make code much clearer, it can't be used in some common situations.

• Only access. Elements can not be assigned to, eg, not to increment each element in a collection.
• Only single structure. It's not possible to traverse two structures at once, eg, to compare two arrays.
• Only single element. Use only for single element access, eg, not to compare successive elements.
• Only forward. It's possible to iterate only forward by single steps.
• At least Java 5. Don't use it if you need compatibility with versions before Java 5.

看來只能讀取， 而不能寫入值。而且不能進行太復雜的操作。