填充 ArrayList [英] Populating ArrayList
问题描述
我正在尝试填充一个数组列表,但是,尽管我通过 main() 声明了它,但我的数组列表始终等于 0,并且从不初始化.
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);
}
谁能告诉我这是怎么回事?我觉得很傻,我已经为我的默认数组做了 ArrayLists,但我无法解决这个问题来挽救我的生命!
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
创建一个 ArrayList
具有初始容量 为 10 但大小仍为 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一个给定大小(初始容量)的数组,因此每次插入新对象时都不需要调整它的大小条目(Java 中的数组不是动态的,因此当您想插入新记录并且数组已满时,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)但即使数组是提前创建的 size()
将返回 0
直到你真正 add()
一些东西到列表中.
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.
这就是为什么这个循环:
That's why this loop:
for (int i = 0; i < array.size(); i++) {
// ...
}
不会执行,因为 array.size()
是 0
.
Will not execute as array.size()
is 0
.
改为:
for (int i = 0; i < 10; i++)
它应该可以工作.
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