import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Random;

public class RandomTest {

  // String 可以為任意類型 也可以自定義類型
  static Map<String, Integer> keyChanceMap = new HashMap<String, Integer>();
  static {
    keyChanceMap.put("aaa", 500);
    keyChanceMap.put("bbb", 1500);
    keyChanceMap.put("ccc", 2000);
    keyChanceMap.put("ddd", 3000);
    keyChanceMap.put("eee", 3000);
  }

  public static void main(String[] args) {
    Map<String, Integer> count = new HashMap<String, Integer>();
    List<String> list = new ArrayList<>();
    String item = null;
    for (int i = 0; i < 10000; i++) {
      item = chanceSelect(keyChanceMap);
      list.add(item);

      if (count.containsKey(item)) {
        count.put(item, count.get(item) + 1);
      } else {
        count.put(item, 1);
      }

    }
    for (String id : count.keySet()) {
      System.out.println(id + "\t出現(xiàn)了 " + count.get(id) + " 次");
    }

    Random rand = new Random();
    int num = rand.nextInt(10000);
    System.out.print("最終選擇的隨機(jī)數(shù)為："+list.get(num));
  }

  public static String chanceSelect(Map<String, Integer> keyChanceMap) {
    if (keyChanceMap == null || keyChanceMap.size() == 0)
      return null;

    Integer sum = 0;
    for (Integer value : keyChanceMap.values()) {
      sum += value;
    }
    // 從1開始
    Integer rand = new Random().nextInt(sum) + 1;

    for (Map.Entry<String, Integer> entry : keyChanceMap.entrySet()) {
      rand -= entry.getValue();
      // 選中
      if (rand <= 0) {
        String item = entry.getKey();
        return item;
      }
    }
    return null;
  }
}