I'm not sure what is going on here. Any enlightenment would be greatly appreciated.
ArrayList<Integer> al = new ArrayList<>();
for(int i = 0; i < 10; i++)
al.add(i);
for(Integer i : al)
System.out.println(al.get(i));
al.add(2,8); //should add the value 8 to index 2?
System.out.println();
for(Integer i : al)
System.out.println(al.get(i));
Output
0
1
2
3
4
5
6
7
8
9
0
1
7
8
2
3
4
5
6
7
8
Why is it adding in 7 and 8...and where did 9 go?
You are getting this behavior because you are calling get() using the very Integers contained in the ArrayList:
for (Integer i : al)
System.out.println(al.get(i)); // i already contains the entry in the ArrayList
al.add(2,8); //should add the value 8 to index 2?
System.out.println();
for (Integer i : al)
System.out.println(al.get(i)); // again, i already contains the ArrayList entry
Change your code to this and all will be fine:
for (Integer i : al)
System.out.println(i);
Output:
0
1
8 <-- you inserted the number 8 at position 2 (third entry),
2 shifting everything to the right by one
3
4
5
6
7
8
9
You are using the enhanced loop, and then printing the value using get; You should either print values at all indexes with get, or use enhanced loop without get. Better yet, use Arrays.toString for printing to avoid this kind of confusion:
for(int i = 0; i < 10; i++)
al.add(i);
Arrays.toString(al);
al.add(2,8);
Arrays.toString(al);
for (Integer i : al)) are really foreach loops... they give you access to the elements of a collection; you don't need to touch the collection within the loop. In other words, eachiis an integer from inside the collection, not an index like in the first (and only) for loop