如何使用继承和构造函数使用具有2个不同大小的1个数组

Question

I need to use a single array to track scores of a game where the indices are the levels of the game. In the parent class, the player is allowed 10 levels. In the child class, they are given 40 additional levels for a total of 50.

This chapter is on inheritance and they also cover constructors. Can a constructor in both parent class and child class change the size of a single array?

I have tried declaring the array to size 50, and then in each constructor allocating memory for the size that I need. [10] and [50] for parent and child classes respectively.

Answer 1

In Java arrays are not extendable, so you can not just "use 1 array with 2 different sizes". You probably want to use ArrayList :

List<Integer> list = new ArrayList<>();

There's also a question to ask: are you sure you need inheritance for this task? You could simply create an array of size you want:

List<Integer> list = new ArrayList<>(40);

But even that is not necessary. The list will grow as needed if there's no space left, so you should not take care about it.

Answer 2

Yes, in the constructor you should just be able redefine it like array = new int[#]

Also, maybe not an exact answer to your question, but you could use a List instead of an array. Java Lists are made to be resizable.

So instead of int[] , you could define it as List<Integer> and not even have to worry about the size.

Answer 3

The lowest level in your hierarchy must give subclasses the option to define the array size.

For example:

package io.medev.stackoverflow;

public class Game1 {

    private final int[] levels;

    public Game1() {
        this(0);
    }

    protected Game1(int additionalLevels) {
        this.levels = new int[10 + additionalLevels];
    }
}

And the subclass:

package io.medev.stackoverflow;

public class Game2 extends Game1 {

    public Game2() {
        this(0);
    }

    protected Game2(int additionalLevels) {
        super(40 + additionalLevels);
    }
}

Like the others already mentioned, I would generally recommend to use a List instead of arrays in this case.