Java ArrayDeque (com exemplos)

Neste tutorial, aprenderemos sobre a classe ArrayDeque e seus métodos com a ajuda de exemplos. Além disso, aprenderemos a usar array deque para implementar uma pilha.

Em Java, podemos usar a ArrayDequeclasse para implementar enfileirar e deque estruturas de dados usando arrays.

Interfaces implementadas por ArrayDeque

A ArrayDequeclasse implementa essas duas interfaces:

• Interface Java Queue
• Interface Java Deque

Criando ArrayDeque

Para criar um array deque, devemos importar o java.util.ArrayDequepacote.

Aqui está como podemos criar um array deque em Java:

 ArrayDeque animal = new ArrayDeque(); 

Aqui, Type indica o tipo de deque da matriz. Por exemplo,

 // Creating String type ArrayDeque ArrayDeque animals = new ArrayDeque(); // Creating Integer type ArrayDeque ArrayDeque age = new ArrayDeque(); 

Métodos de ArrayDeque

A ArrayDequeclasse fornece implementações para todos os métodos presentes em Queuee Dequeinterface.

Inserir Elementos para Deque

1. Adicione elementos usando add (), addFirst () e addLast ()

• add() - insere o elemento especificado no final da matriz deque
• addFirst() - insere o elemento especificado no início do array deque
• addLast()- insere o especificado no final da matriz deque (equivalente a add())

Nota: Se o deque matriz é completa, todos estes métodos add(), addFirst()e addLast()joga IllegalStateException.

Por exemplo,

 import java.util.ArrayDeque; class Main ( public static void main(String() args) ( ArrayDeque animals= new ArrayDeque(); // Using add() animals.add("Dog"); // Using addFirst() animals.addFirst("Cat"); // Using addLast() animals.addLast("Horse"); System.out.println("ArrayDeque: " + animals); ) ) 

Resultado

 ArrayDeque: (gato, cachorro, cavalo) 

2. Insira elementos usando offer (), offerFirst () e offerLast ()

• offer() - insere o elemento especificado no final da matriz deque
• offerFirst() - insere o elemento especificado no início do array deque
• offerLast() - insere o elemento especificado no final da matriz deque

Nota: offer() , offerFirst()e offerLast()retorna truese o elemento é inserido com sucesso; se o deque da matriz estiver cheio, esses métodos retornarão false.

Por exemplo,

 import java.util.ArrayDeque; class Main ( public static void main(String() args) ( ArrayDeque animals= new ArrayDeque(); // Using offer() animals.offer("Dog"); // Using offerFirst() animals.offerFirst("Cat"); // Using offerLast() animals.offerLast("Horse"); System.out.println("ArrayDeque: " + animals); ) ) 

Resultado

 ArrayDeque: (gato, cachorro, cavalo) 

Nota: Se o array deque estiver cheio

• o add()método lançará uma exceção
• o offer()método retornafalse

Acessar elementos ArrayDeque

1. Acesse os elementos usando getFirst () e getLast ()

• getFirst() - retorna o primeiro elemento da matriz deque
• getLast() - retorna o último elemento da matriz deque

Nota: Se a matriz deque estiver vazia, getFirst()e getLast()lança NoSuchElementException.

Por exemplo,

 import java.util.ArrayDeque; class Main ( public static void main(String() args) ( ArrayDeque animals= new ArrayDeque(); animals.add("Dog"); animals.add("Cat"); animals.add("Horse"); System.out.println("ArrayDeque: " + animals); // Get the first element String firstElement = animals.getFirst(); System.out.println("First Element: " + firstElement); // Get the last element String lastElement = animals.getLast(); System.out.println("Last Element: " + lastElement); ) ) 

Resultado

 ArrayDeque: (Cachorro, Gato, Cavalo) Primeiro Elemento: Cachorro Último Elemento: Cavalo 

2. Acesse os elementos usando os métodos peek (), peekFirst () e peekLast ()

• peek() - retorna o primeiro elemento da matriz deque
• peekFirst()- retorna o primeiro elemento da matriz deque (equivalente a peek())
• peekLast() - retorna o último elemento da matriz deque

Por exemplo,

 import java.util.ArrayDeque; class Main ( public static void main(String() args) ( ArrayDeque animals= new ArrayDeque(); animals.add("Dog"); animals.add("Cat"); animals.add("Horse"); System.out.println("ArrayDeque: " + animals); // Using peek() String element = animals.peek(); System.out.println("Head Element: " + element); // Using peekFirst() String firstElement = animals.peekFirst(); System.out.println("First Element: " + firstElement); // Using peekLast String lastElement = animals.peekLast(); System.out.println("Last Element: " + lastElement); ) ) 

Resultado

 ArrayDeque: (Cachorro, Gato, Cavalo) Elemento Head: Cachorro Primeiro Elemento: Cachorro Último Elemento: Cavalo 

Nota: Se a matriz deque estiver vazia peek(), peekFirst()e getLast()lança NoSuchElementException.

Remover elementos ArrayDeque

1. Remova os elementos usando o método remove (), removeFirst (), removeLast ()

• remove() - retorna e remove um elemento do primeiro elemento da matriz deque
• remove(element) - retorna e remove o elemento especificado do cabeçalho do array deque
• removeFirst()- retorna e remove o primeiro elemento da matriz deque (equivalente a remove())
• removeLast() - retorna e remove o último elemento da matriz deque

Note: If the array deque is empty, remove(), removeFirst() and removeLast() method throws an exception. Also, remove(element) throws an exception if the element is not found.

For example,

 import java.util.ArrayDeque; class Main ( public static void main(String() args) ( ArrayDeque animals= new ArrayDeque(); animals.add("Dog"); animals.add("Cat"); animals.add("Cow"); animals.add("Horse"); System.out.println("ArrayDeque: " + animals); // Using remove() String element = animals.remove(); System.out.println("Removed Element: " + element); System.out.println("New ArrayDeque: " + animals); // Using removeFirst() String firstElement = animals.removeFirst(); System.out.println("Removed First Element: " + firstElement); // Using removeLast() String lastElement = animals.removeLast(); System.out.println("Removed Last Element: " + lastElement); ) ) 

Output

 ArrayDeque: (Dog, Cat, Cow, Horse) Removed Element: Dog New ArrayDeque: (Cat, Cow, Horse) Removed First Element: Cat Removed Last Element: Horse 

2. Remove elements using the poll(), pollFirst() and pollLast() method

• poll() - returns and removes the first element of the array deque
• pollFirst() - returns and removes the first element of the array deque (equivalent to poll())
• pollLast() - returns and removes the last element of the array deque

Note: If the array deque is empty, poll(), pollFirst() and pollLast() returns null if the element is not found.

For example,

 import java.util.ArrayDeque; class Main ( public static void main(String() args) ( ArrayDeque animals= new ArrayDeque(); animals.add("Dog"); animals.add("Cat"); animals.add("Cow"); animals.add("Horse"); System.out.println("ArrayDeque: " + animals); // Using poll() String element = animals.poll(); System.out.println("Removed Element: " + element); System.out.println("New ArrayDeque: " + animals); // Using pollFirst() String firstElement = animals.pollFirst(); System.out.println("Removed First Element: " + firstElement); // Using pollLast() String lastElement = animals.pollLast(); System.out.println("Removed Last Element: " + lastElement); ) ) 

Output

 ArrayDeque: (Dog, Cat, Cow, Horse) Removed Element: Dog New ArrayDeque: (Cat, Cow, Horse) Removed First Element: Cat Removed Last Element: Horse 

3. Remove Element: using the clear() method

To remove all the elements from the array deque, we use the clear() method. For example,

 import java.util.ArrayDeque; class Main ( public static void main(String() args) ( ArrayDeque animals= new ArrayDeque(); animals.add("Dog"); animals.add("Cat"); animals.add("Horse"); System.out.println("ArrayDeque: " + animals); // Using clear() animals.clear(); System.out.println("New ArrayDeque: " + animals); ) ) 

Output

 ArrayDeque: (Dog, Cat, Horse) New ArrayDeque: () 

Iterating the ArrayDeque

• iterator() - returns an iterator that can be used to iterate over the array deque
• descendingIterator() - returns an iterator that can be used to iterate over the array deque in reverse order

In order to use these methods, we must import the java.util.Iterator package. For example,

 import java.util.ArrayDeque; import java.util.Iterator; class Main ( public static void main(String() args) ( ArrayDeque animals= new ArrayDeque(); animals.add("Dog"); animals.add("Cat"); animals.add("Horse"); System.out.print("ArrayDeque: "); // Using iterator() Iterator iterate = animals.iterator(); while(iterate.hasNext()) ( System.out.print(iterate.next()); System.out.print(", "); ) System.out.print("ArrayDeque in reverse order: "); // Using descendingIterator() Iterator desIterate = animals.descendingIterator(); while(desIterate.hasNext()) ( System.out.print(desIterate.next()); System.out.print(", "); ) ) ) 

Output

 ArrayDeque: (Dog, Cat, Horse) ArrayDeque in reverse order: (Horse, Cat, Dog) 

Other Methods

Methods	Descriptions
element()	Returns an element from the head of the array deque.
contains(element)	Searches the array deque for the specified element. If the element is found, it returns true, if not it returns false.
size()	Returns the length of the array deque.
toArray()	Converts array deque to array and returns it.
clone()	Creates a copy of the array deque and returns it.

ArrayDeque as a Stack

To implement a LIFO (Last-In-First-Out) stacks in Java, it is recommended to use a deque over the Stack class. The ArrayDeque class is likely to be faster than the Stack class.

ArrayDeque provides the following methods that can be used for implementing a stack.

• push() - adds an element to the top of the stack
• peek() - returns an element from the top of the stack
• pop() - returns and removes an element from the top of the stack

For example,

 import java.util.ArrayDeque; class Main ( public static void main(String() args) ( ArrayDeque stack = new ArrayDeque(); // Add elements to stack stack.push("Dog"); stack.push("Cat"); stack.push("Horse"); System.out.println("Stack: " + stack); // Access element from top of stack String element = stack.peek(); System.out.println("Accessed Element: " + element); // Remove elements from top of stack String remElement = stack.pop(); System.out.println("Removed element: " + remElement); ) ) 

Output

 Stack: (Horse, Cat, Dog) Accessed Element: Horse Removed Element: Horse 

ArrayDeque Vs. LinkedList Class

Both ArrayDeque and Java LinkedList implements the Deque interface. However, there exist some differences between them.

• LinkedList supports null elements, whereas ArrayDeque doesn't.
• Cada nó em uma lista vinculada inclui links para outros nós. É por isso que LinkedListrequer mais armazenamento do que ArrayDeque.
• Se você estiver implementando a fila ou a estrutura de dados deque, um ArrayDequeprovavelmente será mais rápido do que a LinkedList.