Why can we instantiate a stack but not a queue?

Question

Why I can instantiate a stack like this:

Stack<Integer> stack = new Stack<>();

But can't instantiate a queue like this:

Queue<Integer> queue = new Queue<>();

Is that because queue is a interface while stack is a object? If so, why we say that everything in java is an object?

Answer 1

A Queue is an interface, meaning we cannot construct a Queue directly.

We can create object using implementing classes, implements the Queue interface, like one of the following: AbstractQueue, ArrayBlockingQueue, ConcurrentLinkedQueue, DelayQueue, LinkedBlockingQueue, LinkedList, PriorityBlockingQueue, PriorityQueue, or SynchronousQueue.

Stack is the class and can be instantiated directly.

This is by design and with Queue, lot more options are there using implementing classes.