How do I instantiate a Queue object in java

Question

When I try   Queue lt Integer gt  q   new Queue lt Integer gt       the compiler is giving me an error  Any help   Also  if I want to initialize a queue do I have to implement the methods of the queue

User · Answer

Queue is an interface in java  you can not do that   Instead you have two options   option1   Queue lt Integer gt  Q   new LinkedList lt  gt       option2   Queue lt Integer gt  Q   new ArrayDeque lt  gt       I recommend using option2 as it is bit faster than the other

User · Answer

Queue is an interface  you can t explicitly construct a Queue  You ll have to instantiate one of its implementing classes  Something like   Queue linkedList   new LinkedList      Here s a link to the Java tutorial on this subject

User · Answer

A Queue is an interface  which means you cannot construct a Queue directly   The best option is to construct off a class that already implements the Queue interface  like one of the following  AbstractQueue  ArrayBlockingQueue  ArrayDeque  ConcurrentLinkedQueue  DelayQueue  LinkedBlockingQueue  LinkedList  PriorityBlockingQueue  PriorityQueue  or SynchronousQueue   An alternative is to write your own class which implements the necessary Queue interface   It is not needed except in those rare cases where you wish to do something special while providing the rest of your program with a Queue   public class MyQueue lt T extends Tree gt  implements Queue lt T gt       public T element              your code to return an element goes here              public boolean offer T element             your code to accept a submission offer goes here                  etc         An even less used alternative is to construct an anonymous class that implements Queue   You probably don t want to do this  but it s listed as an option for the sake of covering all the bases   new Queue lt Tree gt         public Tree element                        public boolean offer Tree element

User · Answer

Queue is an interface  You can t instantiate an interface directly except via an anonymous inner class  Typically this isn t what you want to do for a collection  Instead  choose an existing implementation  For example   Queue lt Integer gt  q   new LinkedList lt Integer gt       or  Queue lt Integer gt  q   new ArrayDeque lt Integer gt       Typically you pick a collection implementation by the performance and concurrency characteristics you re interested in

User · Answer

The Queue interface extends java util Collection with additional insertion  extraction  and inspection operations like    offer element  E   boolean    Inserting an element   poll    E     Retrieves the element and returns NULL if queue is empty    remove    E    Retrieves and removes the element and throws an Exception if queue is empty    peek    E    Retrieves but does not remove  the head of this queue  returning null if this queue is empty     element    E    Retrieves  but does not remove  the head of this queue  throws an exception if te queue is empty   Example Code for implementing Queue   java util Queue lt String gt  queue   new LinkedList lt  gt     queue offer  Hello    queue offer  StackOverFlow    queue offer  User     System out println queue peek      while  queue size    gt  0       System out println queue remove               Since Queue is empty now so this will return NULL System out println queue peek       Output Of the code    Hello Hello  StackOverFlow  User  null

User · Answer

Queue in Java is defined as an interface and many ready-to-use implementation is present as part of JDK release  Here are some  LinkedList  Priority Queue  ArrayBlockingQueue  ConcurrentLinkedQueue  Linked Transfer Queue  Synchronous Queue etc  SO You can create any of these class and hold it as Queue reference  for example import java util LinkedList  import java util Queue   public class QueueExample     public static void main  String   args      Queue que   new LinkedList      que add  quot first quot      que offer  quot second quot      que offer  quot third quot      System out println  quot Queue Print    quot    que        String head   que element      System out println  quot Head element    quot    head        String element1   que poll      System out println  quot Removed Element    quot    element1        System out println  quot Queue Print after poll    quot    que     String element2   que remove      System out println  quot Removed Element    quot    element2        System out println  quot Queue Print after remove    quot    que           You can also implement your own custom Queue implementing Queue interface

User · Answer

Queue is an interface in java  you could not do that  try   Queue lt Integer gt  Q   new LinkedList lt Integer gt

User · Answer

Queue lt String gt  qe new LinkedList lt String gt      qe add  b    qe add  a    qe add  c      Since Queue is an interface  you can t create an instance of it as you illustrated

[java] How do I instantiate a Queue object in java?

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