BJP5 Exercise 15.17: stretch

Author: Marty Stepp (on 2019/09/19)

Write a method `stretch` that takes an integer n as a parameter and that increases a list of integers by a factor of n by replacing each integer in the original list with n copies of that integer. For example, if a variable called `list` stores this sequence of values:

```[18, 7, 4, 24, 11]
```

And we make the following call:

```list.stretch(3);
```

The list should store the following values after the method is called:

```[18, 18, 18, 7, 7, 7, 4, 4, 4, 24, 24, 24, 11, 11, 11]
```

If the value of n is less than or equal to 0, the list should be empty after the call.

Because adding elements might overrun the capacity of the underlying array, you may need to call `ensureCapacity` to enlarge this array.

Assume you are adding to the `ArrayIntList` class with following fields:

```public class ArrayIntList {
private int[] elementData;
private int size;

public void add(int value) { ... }
public void add(int index, int value) { ... }
public void ensureCapacity(int capacity) { ... }
...