Adding and Getting

We do not use the [] operator with ArrayList.

Instead, we invoke methods on the ArrayList object.

boolean add(E)

The ArrayList below holds Strings, so we can add String objects.

ArrayList<String> strList = new ArrayList<String>();
strList.add("Alice");
strList.add("Mad Hatter");

Each element is added at the end of the list. * As we add, the size of the list grows. * We do not have to worry about adding past the end of the list.

Practice Exercise

add(E) returns a boolean, which is always true.

This doesn't really matter for this class, but there are other classes and interfaces where the value may be false.

E get(index)

We can get elements from the list by their zero-based index.

String firstName = strList.get(0);
String secondName = strList.get(1);

We DO have to consider the number of items in the list, though - like when we use arrays. * Trying to get an index that is negative or too large results in an IndexOutOfBoundsException.

String thirdName = strList.get(2);  // IndexOutOfBoundsException

int size()

We can check the number of elements in an ArrayList with the size() method.

int numElements = strList.size();
System.out.println(numElements);   // 2

Drill

GenericsAndArrayList/com.example.generics.drills.AddingAndGetting

Follow the instructions in comments to practice using ArrayLists.

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