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`.
我发现这个例子生成随机数:
此示例生成特定范围内的随机整数。
import java.util.Random;
/** Generate random integers in a certain range. */
public final class RandomRange {
public static final void main(String... aArgs){
log("Generating random integers in the range 1..10.");
int START = 1;
int END = 10;
Random random = new Random();
for (int idx = 1; idx <= 10; ++idx){
showRandomInteger(START, END, random);
}
log("Done.");
}
private static void showRandomInteger(int aStart, int aEnd, Random aRandom){
if ( aStart > aEnd ) {
throw new IllegalArgumentException("Start cannot exceed End.");
}
//get the range, casting to long to avoid overflow problems
long range = (long)aEnd - (long)aStart + 1;
// compute a fraction of the range, 0 <= frac < range
long fraction = (long)(range * aRandom.nextDouble());
int randomNumber = (int)(fraction + aStart);
log("Generated : " + randomNumber);
}
private static void log(String aMessage){
System.out.println(aMessage);
}
}
此类的示例运行:
Generating random integers in the range 1..10.
Generated : 9
Generated : 3
Generated : 3
Generated : 9
Generated : 4
Generated : 1
Generated : 3
Generated : 9
Generated : 10
Generated : 10
Done.
下面是一个简单的示例,它显示了如何从闭合的[min,max]范围生成随机数,而min<=max为真
您可以将其作为孔中字段类重用,也可以将所有Random.class方法放在一个位置
结果示例:
RandomUtils random = new RandomUtils();
random.nextInt(0, 0); // returns 0
random.nextInt(10, 10); // returns 10
random.nextInt(-10, 10); // returns numbers from -10 to 10 (-10, -9....9, 10)
random.nextInt(10, -10); // throws assert
来源:
import junit.framework.Assert;
import java.util.Random;
public class RandomUtils extends Random {
/**
* @param min generated value. Can't be > then max
* @param max generated value
* @return values in closed range [min, max].
*/
public int nextInt(int min, int max) {
Assert.assertFalse("min can't be > then max; values:[" + min + ", " + max + "]", min > max);
if (min == max) {
return max;
}
return nextInt(max - min + 1) + min;
}
}
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)。