如何在arraylist上使用自己的方法？

Question

public static void arrayReader(Fractions[] array)
    {
        System.out.println("This array has " + array.length + " elements");
        for(int count = 0; count < array.length; count++)
        {
            System.out.println("For cell number " + (count+1));
            array[count] = new Fractions();
            array[count].read();
        }

This is a portion of the code that I wrote. I was told to do the same thing except using ArrayList instead of arrays. So i ran into a problem. how would I be able to do array[count].read();

I tried this but it wouldn't work:

public static void readArray(ArrayList<Fractions> array)
    {
        System.out.println("This array has " + array.size() + " elements");
        for(int count = 0; count < array.size(); count++)
        {
            Fractions fraction = new Fractions();
            fraction.read();
            array.set(count, new Fractions());
            array.add(fraction);
        }
    }

I'm not trying to have you do my homework, I'm genuinly stuck. So please help me understand how this could work.

Answer 1

You can use

array.add(count, new Fractions());

The line above is equivalent to the following line in previous code

array[count] = new Fractions();

That is adding the new Fractions() at a specific index in the ArrayList.

Similarly for the other line

array[count].read();

you will have

(array.get(count)).read();

Answer 2

First of all:

 array[count] = new Fractions();

is not equivalent to:

 array.set(count, new Fractions());
 array.add(fraction);

the arraylist.set method:

Replaces the element at the specified position in this list
 with the specified element.

the arrayList.add method:

Appends the specified element to the end of this list.

Use only :

array.add(fraction);

Then the for cycle is different

If your are doing:

array = new ArrayList(5); //initial capacity

 for(int count = 0; count < array.size(); count++)

the size is 0.

If you are doing:

array = new Fractions[5]; //size

 for(int count = 0; count < array.size(); count++)

the size is 5 .