List

• Create list

List<Integer> rollNumbers = new List<Integer>{11008890, 11008100, 11007231};
System.debug(rollNumbers);

rollNumbers.add(89897767);
rollNumbers.add(89897764);
rollNumbers.add(89897765);

System.debug(rollNumbers);

• Get element at index

// get item on index 1
Integer rollNum = rollNumbers.get(1);
System.debug(rollNum);
System.debug(rollNumbers.get(1));

• Add element at index

// add item on index 4
rollNumbers.add(4, 99990000);
System.debug(rollNumbers);apex

• Length

// get the list size
System.debug(rollNumbers.size());

• Remove at index

// remove the item on index 3
rollNumbers.remove(3);
System.debug(rollNumbers);
System.debug(rollNumbers.size());

• Update at index

// update item on index 1
rollNumbers.set(1, 44444444);
System.debug(rollNumbers);

• Clear

// clear the list
rollNumbers.clear();
System.debug(rollNumbers);
System.debug(rollNumbers.size());

// below line will throw an error
rollNumbers.set(1, 44444444);
System.debug(rollNumbers);