Every ArrayList Method You Need to Know (With Examples)

Before anything, this is the import you need:

import java.util.ArrayList;

And this is how you create one:

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

Simple. Now let's get into the methods.

The Methods

add(element)

Adds an element to the end of the list.

list.add("Apple");

add(index, element)

Adds an element at a specific position. Shifts everything else to the right.

list.add(1, "Banana");

get(index)

Returns the element at that index.

String fruit = list.get(0); // Apple

set(index, element)

Replaces the element at that index with a new one.

list.set(0, "Mango"); // Apple becomes Mango

remove(index)

Removes the element at that index.

list.remove(1); // removes Banana

remove(object)

Removes the first occurrence of that specific value.

list.remove("Mango");

Heads up — if your list is ArrayList<Integer>, Java gets confused between remove(index) and remove(object). Wrap the value: list.remove(Integer.valueOf(5)).

size()

Returns how many elements are in the list.

int count = list.size();

isEmpty()

Returns true if the list has no elements.

boolean empty = list.isEmpty();

contains(object)

Returns true if the list has that value.

boolean has = list.contains("Apple");

indexOf(object)

Returns the index of the first occurrence. Returns -1 if not found.

int pos = list.indexOf("Apple");

lastIndexOf(object)

Returns the index of the last occurrence. Useful when duplicates exist.

int lastPos = list.lastIndexOf("Apple");

clear()

Removes everything. List becomes empty.

list.clear();

addAll(collection)

Adds all elements from another collection into this list.

ArrayList<String> more = new ArrayList<>();
more.add("Grapes");
more.add("Papaya");
list.addAll(more);

addAll(index, collection)

Same as above but inserts at a specific position.

list.addAll(1, more);

removeAll(collection)

Removes all elements that exist in the given collection.

list.removeAll(more);

retainAll(collection)

Keeps only the elements that exist in the given collection. Removes everything else.

list.retainAll(more);

containsAll(collection)

Returns true if this list contains every element in the given collection.

boolean hasAll = list.containsAll(more);

toArray()

Converts the ArrayList into a plain array.

Object[] arr = list.toArray();

subList(fromIndex, toIndex)

Returns a portion of the list. fromIndex is included, toIndex is not.

List<String> part = list.subList(0, 2); // index 0 and 1 only

Collections.sort(list)

Not an ArrayList method exactly, but used all the time. Sorts the list in ascending order.

import java.util.Collections;
Collections.sort(list);

Collections.reverse(list)

Reverses the order of elements.

Collections.reverse(list);

Quick Reference Table