[英]Picking out a random element from an organised ArrayList
So the idea here is that I have an ArrayList with a set of words, I want to sort the list so that it only includes entries with even numbered indecies and then picks out an entry at random. 所以这里的想法是,我有一个带有一组单词的ArrayList,我想对列表进行排序,以便它只包括带有偶数编号的索引的条目,然后随机选择一个条目。 I gave this a bash and I managed to get it to show only odd entries like so:
我给了它一个bash,我设法使其仅显示如下所示的奇数项:
int i = 0;
for (Iterator<Phrase> it = phrases.iterator(); it.hasNext(); i++)
{
Phrase current = it.next();
if (i % 2 == 0)
{
System.out.println(current);
}
}
And this prints off every odd numbered element on the ArrayList which is fine, but I don't know how to select one at random from the odd numbered ones. 并且这会打印出ArrayList上的每个奇数元素,这很好,但是我不知道如何从奇数元素中随机选择一个。 This is what I tried putting into the if statement but it doesn't do what I want it to, it does print off the elements at random but it also includes the odd numbered elements when I only want the even ones
这是我尝试放入if语句中的内容,但没有达到我想要的效果,它会随机打印出元素,但是当我只需要偶数元素时,它还会包含奇数元素
Random r = new Random();
int x = r.nextInt(phrases.size());
System.out.println(phrases.get(x));
Any help would be very appreciated here, thanks. 在这里,任何帮助将不胜感激,谢谢。
but I don't know how to select one at random from the odd numbered ones.
但我不知道如何从奇数中随机选择一个。
what about ensuring x
to be half of the size and multiply it with 2
to have the even index. 如何确保
x
为大小的一半并将其乘以2
以获得偶数索引呢? Try the following: 请尝试以下操作:
Random r = new Random();
int x = r.nextInt(phrases.size()/2) + (list.size() & 1) - 1;
// size is divided by 2
// so that x is randomly 0 to (size/2 -1) inclusive
System.out.println(phrases.get(x * 2)); // ensuring the accessing index are even
You could loop until you get one, but technically, that may never happen. 您可以循环直到获得一个,但从技术上讲,这可能永远不会发生。 So instead, just make sure x is a multiple of 2.
因此,只需确保x是2的倍数即可。
Random r = new Random();
int x = r.nextInt(phrases.size()); // Might be even or odd
x = x % 2 != 0 ? x + 1 : x; // if x is not divisible by 2, x + 1, else x
// x is is now a multiple of two
if(x >= phrases.size()){ // make sure x is still within the
// index boundaries.
x = x-2;
if(x < 0){
x = 0;
}
}
System.out.println(phrases.get(x));
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