Collections

Arrays

Arrays have a fixed size.

int[] numbers = {1, 2, 3, 4};

Access an element using its index.

System.out.println(numbers[0]);

Indexes start at 0.

ArrayLists

An ArrayList can grow or shrink as needed.

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

Add values:

names.add("Alex");
names.add("Sam");

Access values:

System.out.println(names.get(0));

Remove values:

names.remove(0);

Lists

You'll often declare an ArrayList using the List interface.

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

This makes it easier to switch to a different list implementation later.

Looping Through a Collection

for (String name : names) {
    System.out.println(name);
}

FTC Example

You may store motors in a list to perform the same action on all of them.

for (DcMotor motor : driveMotors) {
    motor.setPower(0);
}

Key Takeaways

• Arrays have a fixed size.
• ArrayLists can change size.
• Lists store groups of related objects.
• Use loops to process collections efficiently.