Cannot instantiate the type

Question

When I try to run this code   import java io    import java util     public class TwoColor       public static void main String   args                  Queue lt Edge gt  theQueue   new Queue lt Edge gt                public class Edge                 u and v are the vertices that make up this edge          private int u          private int v             Constructor method         public Edge int newu  int newv                        u   newu              v   newv                      I get this error   Exception in thread  main  java lang Error  Unresolved compilation problem       Cannot instantiate the type Queue     at TwoColor main TwoColor java 8   I don t understand why I can t instantiate the class    It seems right to me

User · Accepted Answer

java util Queue is an interface so you cannot instantiate it directly  You can instantiate a concrete subclass  such as LinkedList   Queue lt T gt  q   new LinkedList lt T gt

User · Answer

You are trying to instantiate an interface  you need to give the concrete class that you want to use i e  Queue lt Edge gt  theQueue   new LinkedBlockingQueue lt Edge gt

User · Answer

You can use   Queue thequeue   new linkedlist      or  Queue thequeue   new Priorityqueue      Reason  Queue is an interface  So you can instantiate only its concrete subclass

User · Answer

I had the very same issue   not being able to instantiate the type of a class which I was absolutely sure was not abstract  Turns out I was implementing an abstract class from Java util instead of implementing my own class  So if the previous answers did not help you  please check that you import the class you actually wanted to import  and not something else with the same name that you IDE might have hinted you  For example  if you were trying to instantiate the class Queue from the package myCollections which you coded yourself   import java util       replace this line import myCollections Queue     by this line       Queue lt Edge gt  theQueue   new Queue lt Edge gt

User · Answer

Queue is an Interface not a class

User · Answer

Queue is an Interface so you can not initiate it directly  Initiate it by one of its implementing classes   From the docs all known implementing classes    AbstractQueue  ArrayBlockingQueue ArrayDeque ConcurrentLinkedQueue DelayQueue LinkedBlockingDeque LinkedBlockingQueue LinkedList PriorityBlockingQueue PriorityQueue SynchronousQueue   You can use any of above based on your requirement to initiate a Queue object

[java] "Cannot instantiate the type..."

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