如何生成int特定范围内的随机值?
我尝试了以下方法,但这些都不起作用:
尝试1:
randomNum = minimum + (int)(Math.random() * maximum);
错误:randomNum可以大于maximum.
randomNum
maximum
尝试2:
Random rn = new Random(); int n = maximum - minimum + 1; int i = rn.nextInt() % n; randomNum = minimum + i;
错误:randomNum可以小于minimum.
minimum
在Java 1.7 或更高版本中,执行此操作的标准方法如下:
import java.util.concurrent.ThreadLocalRandom; // nextInt is normally exclusive of the top value, // so add 1 to make it inclusive int randomNum = ThreadLocalRandom.current().nextInt(min, max + 1);
请参阅相关的 JavaDoc。这种方法的优点是不需要显式初始化java.util.Random实例,如果使用不当,可能会造成混乱和错误。
java.util.Random
但是,相反,没有办法明确设置种子,因此在测试或保存游戏状态或类似情况等有用的情况下,可能难以重现结果。在这些情况下,可以使用下面所示的 Java 1.7 之前的技术。
在 Java 1.7 之前,执行此操作的标准方法如下:
import java.util.Random; /** * Returns a pseudo-random number between min and max, inclusive. * The difference between min and max can be at most * <code>Integer.MAX_VALUE - 1</code>. * * @param min Minimum value * @param max Maximum value. Must be greater than min. * @return Integer between min and max, inclusive. * @see java.util.Random#nextInt(int) */ public static int randInt(int min, int max) { // NOTE: This will (intentionally) not run as written so that folks // copy-pasting have to think about how to initialize their // Random instance. Initialization of the Random instance is outside // the main scope of the question, but some decent options are to have // a field that is initialized once and then re-used as needed or to // use ThreadLocalRandom (if using at least Java 1.7). // // In particular, do NOT do 'Random rand = new Random()' here or you // will get not very good / not very random results. Random rand; // nextInt is normally exclusive of the top value, // so add 1 to make it inclusive int randomNum = rand.nextInt((max - min) + 1) + min; return randomNum; }
请参阅相关的 JavaDoc。在实践中,java.util.Random类通常比java.lang.Math.random()更可取。
java.lang.Math.random()
特别是,当标准库中有一个简单的 API 来完成任务时,不需要重新发明随机整数生成轮。