add - Java ArrayList Method

TLDR

Appends an element to the end of a list.

// Method Signature
boolean add(E element)

Usage

The ArrayList add appends an element to the end of a list.

// Method Signature
boolean add(E element)

// Code Example

// Create an ArrayList of Integers
ArrayList<Integer> list = new ArrayList<>();

// add 2 to list
list.add(2);

// prints [2]
System.out.println(list);

// add 6 to list
list.add(6);

// prints [2, 6]
System.out.println(list);

// add 4 to list
list.add(4);

// prints [2, 6, 4]
System.out.println(list);

In the code example above, we create an Integer ArrayList and use the add method to append integers to the list. Each add method call appends an integer to the end of the list.

Parameters

This method takes one parameter called element:

• element is appended to the end of the ArrayList.
• element should be compatible with the type passed to the ArrayList.

// Parameters Example

// create an ArrayList with a String type
ArrayList<String> list = new ArrayList<>();

// "study" is compatiable with a String
list.add("study");

// prints [study]
System.out.println(list);

// "pain" is added to the end
list.add("pain");

// prints [study, pain]
System.out.println(list);

In the example above, the type passed to the ArrayList is String, so each element must be compatible with the String type.

Returns

The return type of this method is a boolean.

Even though the return type is a boolean, the add method will always return true.

// Returns Example

// Create an ArrayList with a Double type
ArrayList<Double> list = new ArrayList<>();

// prints true
System.out.println(list.add(5.3));

The boolean return type comes from the Collection Interface that ArrayList implements. Returning true or false works for other collection types like Sets, where true is returned if the element is added, and false is returned if the element already exists. The ArrayList add method will always add the element, so it only returns true.