初始化Vector上的ArrayIndexOutOfBoundsException

问题描述

我有这个：

public class DoubleList<Key, Elem> implements ADTDoubleList<Key, Elem> {

    private Vector<Node<Key, Elem>> leftRight = new Vector<Node<Key, Elem>>(2);
    private int[] numLeftNumRight = new int[2];

    public DoubleList() {
        this.leftRight.set(0, null);
        this.leftRight.set(1, null);
        this.numLeftNumRight[0] = 0;
        this.numLeftNumRight[1] = 0;
    }
}

并抛出ArrayIndexOutOfBoundsException。

and it throws an ArrayIndexOutOfBoundsException.

我不知道为什么。有人可以帮帮我吗？

I don't know why. Could someone help me?

推荐答案

你不能在 Vector 或任何其他列表如果该索引尚未被占用。通过使用 new Vector< Node< Key，Elem>>（2），您确保向量最初具有两个元素的容量 ，但它仍然是空的，所以获取 ting或设置使用任何索引都不会起作用。

You can't set an element in a Vector or any other List if that index isn't already occupied. By using new Vector<Node<Key, Elem>>(2) you're ensuring that the vector initially has the capacity for two elements, but it is still empty and so getting or setting using any index won't work.

换句话说，该列表还没有大到足以使该索引有效。改为使用：

In other words, the list hasn't grown big enough for that index to be valid yet. Use this instead:

this.leftRight.add(null);  //index 0
this.leftRight.add(null);  //index 1

你也可以这样做：

this.leftRight.add(0, null);
this.leftRight.add(1, null);

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