RandomUtil.java

package com.hypixel.hytale.common.util;

import java.security.SecureRandom;
import java.util.Arrays;
import java.util.List;
import java.util.Random;
import java.util.concurrent.ThreadLocalRandom;
import javax.annotation.Nonnull;
import javax.annotation.Nullable;

public class RandomUtil {
   public static final ThreadLocal<SecureRandom> SECURE_RANDOM = ThreadLocal.withInitial(SecureRandom::new);

   public RandomUtil() {
   }

   public static <T> T roll(int roll, T[] data, @Nonnull int[] chances) {
      ++roll;
      int lower = 0;
      int upper = 0;

      for(int i = 0; i < chances.length; ++i) {
         int thisOne = chances[i];
         upper += thisOne;
         if (roll > lower && roll <= upper) {
            return (T)data[i];
         }

         lower += thisOne;
      }

      throw new AssertionError("Reached end of roll(" + roll + ", " + Arrays.toString(data) + ", " + Arrays.toString(chances) + ")!");
   }

   public static int rollInt(int roll, int[] data, @Nonnull int[] chances) {
      ++roll;
      int lower = 0;
      int upper = 0;

      for(int i = 0; i < chances.length; ++i) {
         int thisOne = chances[i];
         upper += thisOne;
         if (roll > lower && roll <= upper) {
            return data[i];
         }

         lower += thisOne;
      }

      throw new AssertionError("Reached end of roll(" + roll + ", " + Arrays.toString(data) + ", " + Arrays.toString(chances) + ")!");
   }

   public static SecureRandom getSecureRandom() {
      return (SecureRandom)SECURE_RANDOM.get();
   }

   public static <T> T selectRandom(@Nonnull T[] arr, @Nonnull Random random) {
      return (T)arr[random.nextInt(arr.length)];
   }

   @Nullable
   public static <T> T selectRandomOrNull(@Nonnull T[] arr, @Nonnull Random random) {
      int index = random.nextInt(arr.length + 1);
      return (T)(index == arr.length ? null : arr[index]);
   }

   public static <T> T selectRandom(@Nonnull List<? extends T> list) {
      return (T)selectRandom(list, ThreadLocalRandom.current());
   }

   public static <T> T selectRandom(@Nonnull List<? extends T> list, @Nonnull Random random) {
      return (T)list.get(random.nextInt(list.size()));
   }
}