Array vs ArrayList

Arrays and ArrayLists are very similar. * In fact, an ArrayList contains an array for storing elements. * We say the ArrayList is backed by an array. * ArrayList's main job is to manage the internal array so we don't have to.

The table below compares array operations to ArrayList operations.

• i is an integer index
• arr is an array
• list is an ArrayList

Op	Array	ArrayList
Size	.length	.size()
Write	arr[i] = obj	list.add(obj)
		list.set(i, obj)
Read	obj = arr[i]	obj = list.get(i)

Enhanced for Loops and ArrayList

An array and an ArrayList can be used in an enhanced for loop (or foreach loop), and the syntax is exactly the same.

String[] sArr = {"A", "B", "C", "D"};
for (String string : sArr) {
  // ...
}

ArrayList<String> list = new ArrayList<>();
list.add("A");
list.add("B");
list.add("C");
list.add("D");

for (String string : list) {
  // ...
}

Practice Exercise

One advantage of using an array over ArrayList is, reading an array element with [] is marginally faster than using ArrayList's get method.

This is because the method call adds an extra step.

String s = sArr[0];       // assignment

String st = list.get(0);  // method call + assignment

Also, an array will usually consume less memory.

Still, the ability of an ArrayList to grow dynamically outweighs this advantage.

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