Difference between Array and ArrayList in detail?

• Arrays are fixed sized; set during initialization. ArrayList is variable sized. It is created with a default size.
• But as ArrayList is backed by an array, a resize operation slows down the performance as it involves creation of new array and copy of content from old to new array.
• Primitives cannot be stored in ArrayList. Only Objects can be stored in ArrayList. Arrays can store both primitives and Objects

• JVM through Autoboxing(converting primitives to equivalent objects internally) ensures that only objects are added to the arraylist object.

  
    ArrayList  arraylistobject = new ArrayList();`
    arraylistobject.add(23);  // try to add 23 (primitive)
    

• Generics cannot be used with array.
  ArrayStoreException is thrown when an attempt to store a different type in an array is made. ArrayList allows you to use Generics to ensure type-safety.

• Performance of arrays is higher compared to ArrayList
• Arrays are multi-dimensional
• Syntax related: Size of array: array.length; Size of ArrayList: arrayList.size();

  
    Array: array[i] = object;
    ArrayList: arrayList.add(object);
    

Instantiate Queue using Java Collections

A Queue is an interface, which means you cannot construct a Queue directly except via an anonymous inner class.

The best option is to construct off a class that already implements the Queue interface, like one of the following: ArrayDeque, LinkedList, AbstractQueue, ArrayBlockingQueue, ConcurrentLinkedQueue, DelayQueue, LinkedBlockingQueue, PriorityBlockingQueue, PriorityQueue, or SynchronousQueue. For example:

Queue q = new LinkedList();
    or
Queue q = new ArrayDeque();

Typically you pick a collection implementation by the performance and concurrency characteristics you're interested in.