ArrayList

Learn dynamic arrays with ArrayList.

Dynamic array: ArrayList

When you want a list that grows automatically instead of a fixed-length int[], you use ArrayList. The java.util.ArrayList class expands itself as you add elements.

ArrayList<String> names = new ArrayList<>();
names.add("Ayşe");
names.add("Mehmet");
// [Ayşe, Mehmet]

The type goes inside angle brackets: ArrayList<String>. This guarantees only String can be added. For primitive types you use wrapper classes: Integer, Double, Boolean.

Why is ArrayList practical?

With fixed-length arrays, adding an element means creating a new array and copying the old one. ArrayList does this for you; it offers ready methods like add, remove and size.

ArrayList<Integer> nums = new ArrayList<>();
nums.add(10);
nums.add(20);
int first = nums.get(0);
// first = 10

To print the list, just System.out.println(nums); the toString method is called automatically and produces a bracketed output.

Exercise Build a customer list

Create an ArrayList<String>, add "Ayşe", "Mehmet" and "Zeynep", then print the list.

Show example solution

ArrayList<String> names = new ArrayList<>();
names.add("Ayşe");
names.add("Mehmet");
names.add("Zeynep");
System.out.println(names);

Test yourself

Fill in the blank: declare the list

ArrayList<String> names = new ArrayList____();

Show answer

ArrayList<String> names = new ArrayList<>();

Match method to purpose

add(x)

Adds an element to the list
get(i)

Returns the element at index i
size()

Returns the number of elements
remove(i)

Removes the element at index i
What is needed to add a primitive int to an ArrayList?
- Convert it to an int[] first
- Use the Integer wrapper
- Declare the list as ArrayList<int>
- Make the list static
Show answer

Use the Integer wrapper — Generics do not accept primitive types; use Integer.

Next lesson: add and get

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