如何在特定范围内生成随机int值？
以下方法存在与整数溢出相关的错误：
randomNum = minimum + (int)(Math.random() * maximum);
// Bug: `randomNum` can be bigger than `maximum`.
Random rn = new Random();
int n = maximum - minimum + 1;
int i = rn.nextInt() % n;
randomNum = minimum + i;
// Bug: `randomNum` can be smaller than `minimum`.
当前回答
我已经创建了一个方法来获取给定范围内的唯一整数。
/*
* minNum is the minimum possible random number
* maxNum is the maximum possible random number
* numbersNeeded is the quantity of random number required
* the give method provides you with unique random number between min & max range
*/
public static Set<Integer> getUniqueRandomNumbers( int minNum , int maxNum ,int numbersNeeded ){
if(minNum >= maxNum)
throw new IllegalArgumentException("maxNum must be greater than minNum");
if(! (numbersNeeded > (maxNum - minNum + 1) ))
throw new IllegalArgumentException("numberNeeded must be greater then difference b/w (max- min +1)");
Random rng = new Random(); // Ideally just create one instance globally
// Note: use LinkedHashSet to maintain insertion order
Set<Integer> generated = new LinkedHashSet<Integer>();
while (generated.size() < numbersNeeded)
{
Integer next = rng.nextInt((maxNum - minNum) + 1) + minNum;
// As we're adding to a set, this will automatically do a containment check
generated.add(next);
}
return generated;
}
其他回答
你可以使用
RandomStringUtils.randomNumeric(int count)
该方法也来自Apache Commons。
使用Java 8 IntStream和Collections.shuffle的不同方法
import java.util.stream.IntStream;
import java.util.ArrayList;
import java.util.Collections;
public class Main {
public static void main(String[] args) {
IntStream range = IntStream.rangeClosed(5,10);
ArrayList<Integer> ls = new ArrayList<Integer>();
//populate the ArrayList
range.forEach(i -> ls.add(new Integer(i)) );
//perform a random shuffle using the Collections Fisher-Yates shuffle
Collections.shuffle(ls);
System.out.println(ls);
}
}
Scala中的等价项
import scala.util.Random
object RandomRange extends App{
val x = Random.shuffle(5 to 10)
println(x)
}
可以使用以下代码：
ThreadLocalRandom.current().nextInt(rangeStart, rangeEndExclusive)
Use:
Random ran = new Random();
int x = ran.nextInt(6) + 5;
整数x现在是可能结果为5-10的随机数。
Java中的Math.Random类是基于0的。所以，如果你这样写：
Random rand = new Random();
int x = rand.nextInt(10);
x将介于0-9之间（含0-9）。
因此，给定以下25项的数组，生成0（数组的基数）和array.length之间的随机数的代码为：
String[] i = new String[25];
Random rand = new Random();
int index = 0;
index = rand.nextInt( i.length );
由于i.length将返回25，因此nextInt（i.length）将返回0-24之间的数字。另一个选项是Math.Random，其工作方式相同。
index = (int) Math.floor(Math.random() * i.length);
为了更好地理解，请查看论坛帖子Random Intervals（archive.org）。
