Introduction to Lists

A List is an ordered collection of values. Instead of creating a separate variable for every value, you can keep many values together in one place and reach each of them by position.

Creating a List

You declare a list by naming the type of value it holds inside angle brackets. This list holds Integer values:

List<Integer> scores = new List<Integer>();

The list starts empty. You can also fill it as you create it:

List<String> colors = new List<String>{ 'red', 'green', 'blue' };

Adding Values

Use the add method to place a value at the end of the list:

List<String> names = new List<String>();
names.add('Ada');
names.add('Grace');
// names now holds 'Ada' then 'Grace'

Size and Position

Every item has an index that describes its position. The first item is at index 0, the second at index 1, and so on. Use size to count the items and get to read the item at a position:

System.debug(names.size()); // 2
System.debug(names.get(0)); // Ada
System.debug(names.get(1)); // Grace

Why This Matters

Lists let you group related values and work with them as a unit. Because each value has a position, you can add to the list, count what is inside, and read any item you need.