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
Random random = new Random();
int max = 10;
int min = 3;
int randomNum = random.nextInt(max) % (max - min + 1) + min;
最好使用SecureDrandom，而不仅仅是Random。
public static int generateRandomInteger(int min, int max) {
SecureRandom rand = new SecureRandom();
rand.setSeed(new Date().getTime());
int randomNum = rand.nextInt((max - min) + 1) + min;
return randomNum;
}
在java-8中，他们在Random类中引入了方法int（int randomNumberOrigin，int randomNumber Bound）。
例如，如果要生成[0，10]范围内的五个随机整数（或单个整数），只需执行以下操作：
Random r = new Random();
int[] fiveRandomNumbers = r.ints(5, 0, 11).toArray();
int randomNumber = r.ints(1, 0, 11).findFirst().getAsInt();
第一个参数仅指示生成的IntStream的大小（这是生成无限IntStream的重载方法）。
如果需要执行多个单独的调用，可以从流中创建无限基元迭代器：
public final class IntRandomNumberGenerator {
private PrimitiveIterator.OfInt randomIterator;
/**
* Initialize a new random number generator that generates
* random numbers in the range [min, max]
* @param min - the min value (inclusive)
* @param max - the max value (inclusive)
*/
public IntRandomNumberGenerator(int min, int max) {
randomIterator = new Random().ints(min, max + 1).iterator();
}
/**
* Returns a random number in the range (min, max)
* @return a random number in the range (min, max)
*/
public int nextInt() {
return randomIterator.nextInt();
}
}
您也可以对双值和长值执行此操作。
您可以在Java 8中简洁地实现这一点：
Random random = new Random();
int max = 10;
int min = 5;
int totalNumber = 10;
IntStream stream = random.ints(totalNumber, min, max);
stream.forEach(System.out::println);
rand.nextInt((max+1) - min) + min;
