ArrayDeque in Java

ArrayDeque is a class in Java’s java.util package that implements the Deque interface. It is a resizable-array implementation of the Deque interface, which means that it provides a dynamic array that can grow or shrink as needed. In this answer, I will explain how to use ArrayDeque in Java, as well as some of its commonly used methods.

Creating an ArrayDeque

To use ArrayDeque in Java, you must first import the java.util.ArrayDeque class. You can create a new ArrayDeque by instantiating the class with a type parameter that specifies the type of elements the deque will hold. Here’s an example of how to create a new ArrayDeque that can hold elements of type String:

ArrayDeque<String> deque = new ArrayDeque<>();

Adding and Removing Elements

Once an ArrayDeque has been created, elements can be added or removed from it using the following methods:

// Add an element to the end of the deque
deque.add("apple");

// Add an element to the front of the deque
deque.addFirst("banana");

// Add an element to the end of the deque, equivalent to add()
deque.offer("cherry");

// Add an element to the front of the deque, equivalent to addFirst()
deque.offerFirst("date");

// Remove and return the first element in the deque
String first = deque.poll();

// Remove and return the last element in the deque
String last = deque.pollLast();

// Remove the first occurrence of an element
boolean success = deque.remove("banana");

// Remove and return the first element in the deque, throws an exception if the deque is empty
first = deque.remove();

// Remove and return the last element in the deque, throws an exception if the deque is empty
last = deque.removeLast();

// Remove all elements from the deque
deque.clear();

Accessing Elements

ArrayDeque provides several methods to access elements in the deque:

// Get the number of elements in the deque
int size = deque.size();

// Check if the deque is empty
boolean isEmpty = deque.isEmpty();

// Get the first element in the deque without removing it
String first = deque.peek();

// Get the last element in the deque without removing it
String last = deque.peekLast();

// Get the element at the specified index
String element = deque.get(1);

// Convert the deque to an array
String[] array = deque.toArray(new String[0]);

// Iterate over the elements in the deque using a for-each loop
for (String element : deque) {
    System.out.println(element);
}

Other Commonly Used Methods

Some other commonly used methods provided by the ArrayDeque class include:

// Get the element at the specified index, equivalent to get()
element = deque.get(1);

// Set the element at the specified index
deque.set(1, "elderberry");

// Remove and return the first element in the deque without throwing an exception if the deque is empty, returns null instead
first = deque.pollFirst();

// Remove and return the last element in the deque without throwing an exception if the deque is empty, returns null instead
last = deque.pollLast();

One important thing to keep in mind when using an ArrayDeque is that it provides a way to store elements as a double-ended queue, which means that it allows efficient insertion and removal of elements at both the front and the end of the queue. However, because it uses a dynamic array, it can be slower than other types of collections for random access to elements, such as when using the get() method. It is also worth noting that ArrayDeque is not thread-safe, which means that it should not be used in multi-threaded environments without proper synchronization.

In addition to ArrayDeque, Java’s java.util package provides several other implementations of the Deque interface that can be used depending on your specific use case. For example, if you need a thread-safe implementation of Deque, you can use ConcurrentLinkedDeque, or if you need an implementation that guarantees constant-time performance for adding or removing elements at the beginning or end of the deque, you can use LinkedList.

Overall, ArrayDeque is a useful data structure in Java for situations where you need a dynamic array that can grow or shrink as needed and provides efficient insertion and removal of elements at both the front and the end of the queue. Its simple and intuitive API makes it easy to use, and its efficient implementation makes it a good choice for many applications.