填充ArrayList [英] Populating ArrayList

问题描述

我正在尝试填充数组列表，但是，尽管我通过main()声明了数组列表，但数组列表始终等于0，并且从未初始化.

I am trying to populate an array list, however, my array list constantly equals 0, and never initializes, despite my declaring it over main().

这是我的代码.

static ArrayList<Integer> array = new ArrayList<Integer>(10); //The parenthesis value changes the size of the array.
static Random randomize = new Random(); //This means do not pass 100 elements.

public static void main (String [] args)
{
    int tally = 0;
    int randInt = 0;

    randInt = randomize.nextInt(100); //Now set the random value.
    System.out.println(randInt); //Made when randomizing number didn't work.
    System.out.println(array.size() + " : Array size");

    for (int i = 0; i < array.size(); i++)
    {
        randInt = randomize.nextInt(100); //Now set the random value.
        array.add(randInt);
        tally = tally + array.get(i); //add element to the total in the array.
    }       
    //System.out.println(tally);
}

有人可以告诉我怎么回事吗?我觉得很傻，我已经为默认数组完成了ArrayLists，但我想不出这点来挽救我的生命！

Can someone tell me what is going on? I feel rather silly, I've done ArrayLists for my default arrays and I cannot figure this out to save my life!

推荐答案

new ArrayList<Integer>(10)创建初始容量为10的ArrayList，但是大小仍然为0，因为其中没有元素

new ArrayList<Integer>(10) creates an ArrayList with initial capacity of 10 but the size is still 0 as there are no elements in it.

ArrayList由下面的数组支持，因此在构造对象时它确实创建了给定大小(初始容量)的数组，因此不需要在每次插入新条目时调整其大小(Java中的数组)是不是动态的，因此当您要插入新记录且阵列已满时，您需要创建一个新记录并移动所有项目，这是一项昂贵的操作)，即使阵列是在前面创建的时间size()会返回0，直到您实际上将add()列表中的某物为止.

ArrayList is backed by an array underneath so it does create an array of a given size (initial capacity) when constructing the object so it doesn't need to resize it every time you insert a new entry (arrays in Java are not dynamic so when you want to insert a new record and the array is full you need to create a new one and move all the items, that's an expensive operation) but even though the array is created ahead of time size() will return 0 until you actually add() something to the list.

这就是该循环的原因:

for (int i = 0; i < array.size(); i++) {
 // ...
}

将不会执行，因为array.size()是0.

将其更改为:

for (int i = 0; i < 10; i++)

它应该可以工作.

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