package com.firefly.utils;
abstract public class RandomUtils {
public static final String ALL_CHAR = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
/**
* Generates a random number from a specified range
*
* @param min
* The minimal number of the range
* @param max
* The maximal number of the range
* @return A random number from minimal number to maximal number, which contains minimal and maximal number.
*/
public static long random(long min, long max) {
return Math.round(ThreadLocalRandom.current().nextDouble()
* (max - min) + min);
}
/**
* Returns a index of a specified probability, e.g. the string is "100:1:32:200:16:30".
* If it returns 0 that probability is 100/(100+1+32+200+16+30)
*
* @param conf
* Configures specified probability
* @return The index of a specified probability
*/
public static int randomSegment(String conf) {
String[] tmp = StringUtils.split(conf, ":");
int[] probability = new int[tmp.length];
for (int i = 0; i < probability.length; i++)
probability[i] = Integer.parseInt(tmp[i].trim());
return randomSegment(probability);
}
/**
* Returns the index of array that specifies probability.
*
* @param probability
* The element of array represents the probability.
* @return The index of array.
*/
public static int randomSegment(int[] probability) {
int total = 0;
for (int i = 0; i < probability.length; i++) {
total += probability[i];
probability[i] = total;
}
int rand = (int) random(0, total - 1);
for (int i = 0; i < probability.length; i++) {
if (rand < probability[i]) {
return i;
}
}
return -1;
}
/**
* Returns a random string.
*
* @param length
* The random string's length
* @return A random string.
*/
public static String randomString(int length) {
StringBuilder sb = new StringBuilder();
for (int i = 0; i < length; i++) {
int index = (int) random(0, ALL_CHAR.length() - 1);
sb.append(ALL_CHAR.charAt(index));
}
return sb.toString();
}
public static void main(String[] args) {
String conf = "100:1:32:200:16:30";
System.out.println(randomSegment(conf));
System.out.println(random(0, 5));
System.out.println(randomString(16));
}
}