WeightedRandomEvents.java

import org.jetbrains.annotations.NotNull;

import java.util.*;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.atomic.AtomicInteger;

public class WeightedRandomEvents<A> {
  
  private final Map<Integer, Consumer<A>> events;
  
  public WeightedRandomEvents(@NotNull Map<Integer, Consumer<A>> events) {
    this.events = Objects.requireNonNull(events);
    checkSum();
  }
  
  public WeightedRandomEvents(@NotNull List<Integer> percentages, @NotNull List<Consumer<A>> events) {
    this.events = new HashMap<>();
    AtomicInteger i = new AtomicInteger();
    percentages.forEach(p -> this.events.put(p, events.get(i.getAndIncrement())));
    checkSum();
  }
  
  private void checkSum() {
    if (events.keySet().stream().mapToInt(value -> value).sum() > 100)
      throw new IllegalArgumentException("Sum of percentages must be equal or lower than 100!");
  }
  
  public void randomExecute(A input) {
    final int randomNumber = ThreadLocalRandom.current().nextInt(100);
    int temp = 0;
    for (Map.Entry<Integer, Consumer<A>> entry : events.entrySet()) {
      if (temp <= randomNumber && randomNumber < temp + entry.getKey()) {
        entry.getValue().accept(input);
        break;
      } else temp += entry.getKey();
    }
  }
}