Java ArrayDeque (med eksempler)

I denne vejledning lærer vi om ArrayDeque-klassen og dens metoder ved hjælp af eksempler. Vi lærer også at bruge array deque til at implementere en stak.

I Java kan vi bruge ArrayDequeklassen til at implementere kø- og deque-datastrukturer ved hjælp af arrays.

Grænseflader implementeret af ArrayDeque

Den ArrayDequeklasse implementerer disse to grænseflader:

  • Java køgrænseflade
  • Java Deque-interface

Oprettelse af ArrayDeque

For at oprette en array-deque skal vi importere java.util.ArrayDequepakken.

Sådan kan vi oprette en array-deque i Java:

 ArrayDeque animal = new ArrayDeque();

Her angiver Type typen af ​​array-deque. For eksempel,

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

Metoder til ArrayDeque

Den ArrayDequeklasse giver implementeringer for alle metoderne til stede i Queueog Dequeinterface.

Indsæt elementer til Deque

1. Tilføj elementer ved hjælp af add (), addFirst () og addLast ()

  • add() - indsætter det angivne element i slutningen af ​​array-deque
  • addFirst() - indsætter det angivne element i begyndelsen af ​​array-deque
  • addLast()- indsætter det specificerede i slutningen af ​​array-deque (svarende til add())

Bemærk: Hvis array deque er fuld, alle disse metoder add(), addFirst()og addLast()kast IllegalStateException.

For eksempel,

 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); ) )

Produktion

 ArrayDeque: (Kat, hund, hest)

2. Indsæt elementer ved hjælp af offer (), offerFirst () og offerLast ()

  • offer() - indsætter det angivne element i slutningen af ​​array-deque
  • offerFirst() - indsætter det angivne element i begyndelsen af ​​array-deque
  • offerLast() - indsætter det angivne element i slutningen af ​​array-deque

Bemærk: offer() , offerFirst()og offerLast()returnerer truehvis elementet held er indsat; hvis array deque er fuld, vender disse metoder tilbage false.

For eksempel,

 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); ) )

Produktion

 ArrayDeque: (Kat, hund, hest)

Bemærk: Hvis array-deque er fuld

  • den add()metode vil kaste en undtagelse
  • de offer()returnerer fremgangsmådenfalse

Adgang til ArrayDeque Elements

1. Få adgang til elementer ved hjælp af getFirst () og getLast ()

  • getFirst() - returnerer det første element i array-deque
  • getLast() - returnerer det sidste element i array-deque

Bemærk: Hvis array-deken er tom getFirst()og getLast()kaster NoSuchElementException.

For eksempel,

 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); ) )

Produktion

 ArrayDeque: (Hund, kat, hest) Første element: Hund sidste element: hest

2. Få adgang til elementer ved hjælp af peek (), peekFirst () og peekLast () -metoden

  • peek() - returnerer det første element i array-deque
  • peekFirst()- returnerer det første element i array deque (svarende til peek())
  • peekLast() - returnerer det sidste element i array-deque

For eksempel,

 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); ) )

Produktion

 ArrayDeque: (Hund, kat, hest) Hovedelement: Hund første element: Hund sidste element: hest

Bemærk: Hvis array-deken er tom peek(), peekFirst()og getLast()kaster NoSuchElementException.

Fjern ArrayDeque Elements

1. Fjern elementer ved hjælp af metoden remove (), removeFirst (), removeLast ()

  • remove() - returnerer og fjerner et element fra det første element i array-deque
  • remove(element) - returnerer og fjerner det angivne element fra hovedet på array-deque
  • removeFirst()- returnerer og fjerner det første element fra array deque (svarende til remove())
  • removeLast() - returnerer og fjerner det sidste element fra array-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.
  • Hver knude på en linket liste indeholder links til andre noder. Derfor LinkedListkræver mere opbevaring end ArrayDeque.
  • Hvis du implementerer køen eller deque-datastrukturen, ArrayDequeer det sandsynligvis hurtigere end en LinkedList.

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