An abstraction of an array?

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this is for a assignment, and one of the tasks is to create a abstraction of a array, does it mean that i am declaring a array that's abstract here, if so how would i declare it

private abstract Array<TYPE> Disk = new Array<TYPE>()

? something like that? or is it impossible to create a abstract array and its talking about making a class abstract and inserting a array in that class

// Build an abstraction of an array of integers on disk. If the file exists, * it should be opened and its length calculated (size parameter is ignored). * If the file doesn't exist, it should be created and size zeros should be * written to the file. ^^ goal here

please don't answer or give me any code, other than a yes or no to declaring that array and wether it would work

java
2 Answers

The given input is a bit sparse, so I can only guess what to do.

An abstraction can be interpreted in multiple ways.

  • To "create an abstract array" is not building an abstraction. Usually an abstract method is used to signify, that this method has no implementation. In this context I think it doesn't make any sense.
  • The same with making an abstract class.

or, as I would argue:

  • You have to create an abstraction of something, which means you want to hide details and/or information. In your case, you have an array of integers, and you want to store it on disk. Furthermore, you have some operations you want to apply to this. This gives you an abstraction. You define an interface (operations) and hide all the rest (array of ints, store on disk). In other words, you abstracted all the details, and provided some easy to use interface.

So In my opinion, you have to create a class having the asked operations, and implement some store/load methods, and return the appropriate results.

user_6770560

You can't have abstract fields like in your example.

About an abstraction over arrays - you might be able to do it, but I don't think it's worth it. Lists and other classes have their type parameters erased at runtime, so you can do all sorts of casting with them. However, arrays know the class of their elements, meaning you can't just do T[] foo = new T[]{} given some type parameter T. You could, of course, cast an Object[] to a T[], but even if that works at compile time, you would get a ClassCastException at runtime.

However, if you have a Class<T> object in addition to some type parameter T, you can use Array.newInstance() to create arrays. Here's one way you could do it, but casting, say, a MyArray<String> to a MyArray<Object>, and then using getArray as an Object[], will cause a class cast exception.

class MyArray<T> {
  private final T[] arr;
  public MyArray(Class<T> klass, int n) {
    arr = (T[]) java.lang.reflect.Array.newInstance(klass, n);
  }
  public T get(int index) {
    return (T) arr[index];
  }
  public void set(int index, T t) {
    arr[index] = t;
  }
}
user_118820020
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