Embedded Files
WHAT IS AN ARRAYLIST?
An ArrayList is a lot like an array. It is a data structure and it starts counting at zero. You can access individual elements by index. It is different because it has a few very useful features:
It contains handy elements to add, remove, clear elements
It is dynamically sized, meaning it can change size after it has been created
As you progress in this course, the ArrayList will become your default data structure.
USING ARRAYLISTS
Declaring and Initialization
To make an ArrayList, you’ll need to both declare and initialize it:
ArrayList<String> words;
words = new ArrayList<String>();
This is often put into a single line:
ArrayList<String> words = new ArrayList<String>();
Notice that there is no initial size. An ArrayList starts out empty.
Iteration
Let’s consider a common example of using an Array-List: looping through the list and printing each element.
for(int i = 0; i < words.size(); i++)
{
System.out.println(words.get(i));
}
Notice that compared to a normal array, it uses the .size() method and .get() method.
ADDITIONAL METHODS
Want to know everything that an ArrayList can do? Check out the official reference.
Size and Contents
size() Returns the number of elements in the list
isEmpty() Returns true if the list is empty, false otherwise
get(int index) Returns the element at index
contains(Object o) Returns true if the list contains an instance of the specified object
indexOf(Object o) Returns the index position of the first instance of the object (-1 otherwise)
Adding
add(Object o) Adds an object to the end of the list
add(int index, Object o) Inserts an object to the list at the specified index, pushing the rest back
set(int index, Object o) Sets the element at the specified index equal to the given object
Removing
clear() Removes all elements from the list
remove(int index) Removes the element at index
remove(Object o) Removes the first instance of o from the list, if it is present
RESOURCES
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