Sorry if it was already asked, but I did not find an answer on stackoveflow and I didn't see official tutorials about this field.
The question is in the title - if we have code like
int[] array = new int[20];
for (int el : array) {
...
}
Will JVM run it as standard for loop
for (int i = 0; i < array.length; i++)
Or it will create an iterator?
UPD This link may be helpful to complete the answer
Fastest way to iterate an Array in Java: loop variable vs enhanced for statement
Arrays in Java don't implement Iterable interface so you cannot get an iterator from an array. Also you cannot have an Iterator over primitive types such as int because a primitive type can't be a generic parameter. E.g. if you want an Iterator, you have to use an Iterator instead, which will result in a lot of autoboxing and -unboxing if that's backed by an int[].
The JVM is unlikely to create iterator for for-each loop over arrays as it would be very inefficient.
In fact the compiler will transform the for-each loop into indexed for loop. You can check it by viewing the decompiled byte code for this method:
Source code:
public void test() {
int[] array = new int[20];
for (int el : array) {
System.out.println("test");
}
}
Decompiled byte-code:
public void test() {
int[] array = new int[20];
int[] var2 = array;
int var3 = array.length;
for(int var4 = 0; var4 < var3; ++var4) {
int var10000 = var2[var4];
System.out.println("lol");
}
}
For-each loop is an iterable form of ordinary for loop, which is a better built data structure.
cars is an array, then for eg: -
for(Car car: cars){
//car.name() = audi...
....
}
is actually the same code shown below...
for(Iterator<Car> iterator = cars.iterator(); iterator.hasNext(); ){
Car car = iterator.next();
//car.name() = audi...
......
}
