在java中为播放列表创建一个shuffle方法

4 回答

• 0

  该程序崩溃，这是因为，在 shuffle 方法中， while (songs.size()>0){ 始终为 true . The size of list is not changed.

  如果你想用自己的方法编写 shuffle 方法，那么一个简单的方法是 iterater the songs list 和 swap 2 songs of current index i and the song with a random index .

  public void shuffle (List<Mp3> songsList)
       {
           for(int i=0;i< songsList.size(); i++)
           {
               //Do something here
                                //generate a random number
               //Swap songs according to the i index and and random index.
           }
       }
  

  最简单的方法是使用 Collections # shuffle 方法使列表随机 .

  Collections中相应的shuffle源代码如下：

  /**
   * Randomly permutes the specified list using a default source of
   * randomness.  All permutations occur with approximately equal
   * likelihood.<p>
   *
   * The hedge "approximately" is used in the foregoing description because
   * default source of randomness is only approximately an unbiased source
   * of independently chosen bits. If it were a perfect source of randomly
   * chosen bits, then the algorithm would choose permutations with perfect
   * uniformity.<p>
   *
   * This implementation traverses the list backwards, from the last element
   * up to the second, repeatedly swapping a randomly selected element into
   * the "current position".  Elements are randomly selected from the
   * portion of the list that runs from the first element to the current
   * position, inclusive.<p>
   *
   * This method runs in linear time.  If the specified list does not
   * implement the {@link RandomAccess} interface and is large, this
   * implementation dumps the specified list into an array before shuffling
   * it, and dumps the shuffled array back into the list.  This avoids the
   * quadratic behavior that would result from shuffling a "sequential
   * access" list in place.
   *
   * @param  list the list to be shuffled.
   * @throws UnsupportedOperationException if the specified list or
   *         its list-iterator does not support the <tt>set</tt> method.
   */
  public static void shuffle(List<?> list) {
      shuffle(list, r);
  }
  

  回复于 2024-04-26T06:54:13+08:00
• 0

  你在那里正确的轨道，但你忘了实施描述的一个步骤：

  remove it from the current playlist and place it at the end of newList
  

  需要将Shuffle方法重写为以下内容：

  public void shuffle (){
      newList = new ArrayList<Mp3> ();
      while (songs.size()>0){
          Mp3 song = songs.get(nextInt(songs.size()));
          songs.remove(song); // the forgotten step
          newList.add(song);
          System.out.println("new list" + newList);
     }
   }
  

  回复于 2024-04-26T06:54:13+08:00
• 0

  import java.util.Random;
  
  public class SuffleSongs {
  
      public static void main(String[] args) {
  
          List<String> playList = new ArrayList<String>();
          playList.add("Song1");
          playList.add("Song2");
          playList.add("Song3");
          playList.add("Song4");
          playList.add("Song5");
          playList.add("Song6");
          playList.add("Song7");
          playList.add("Song8");
          playList.add("Song9");
          playList.add("Song10");
          playList.add("Song11");
          playList.add("Song12");
          playList.add("Song13");
          playList.add("Song14");
          playList.add("Song15");
          playList.add("Song16");
          playList.add("Song17");
          playList.add("Song18");
          playList.add("Song19");
          playList.add("Song20");
          playList.add("Song21");
  
          // shuffle the playlist
          for (int i=0; i<playList.size(); ++i) {
              Random rand = new Random();
              int temp = rand.nextInt(playList.size() -i) + i;
              Collections.swap(playList, i, temp);
          }
  
          // print the shuffled playlist
          for(int j = 0; j < playList.size(); ++j) {
              System.out.println(playList.get(j));
          }
  
      }
  
  }
  

  这将随机播放而无需创建新的播放列表（ArrayList） .
  基本上这个代码只获取一个播放列表ArrayList，然后在同一个ArrayList中随机播放 .

  回复于 2024-04-26T06:54:13+08:00
• -2

  采用洗牌方法来洗牌 . 希望能帮助到你

  public static int[] shuffleDeck(int[] a,int n) {
          for(int i=0;i<52;i++) {
              /* I have taken a number 53 because it is a prime number and greater than 52
               * that is helpful in avoiding collisions i.e repetitive number.
               */
              a[i] = ((i+1)*n)%53;     
          }
          return a;
      }
  

  回复于 2024-04-26T06:54:13+08:00