随机播放或随机化Java的列表

• 改组列表
  Collections.shuffle()用于对Java的列表进行混洗。

  类层次结构：

  java
     ↳ util
        ↳ Collections
  

  句法：

  Collections.shuffle(list);
  

  例子：

  // Java program to demonstrate working of shuffle()
  import java.util.*;
    
  public class GFG {
      public static void main(String[] args)
      {
          ArrayList mylist = new ArrayList();
          mylist.add("ide");
          mylist.add("quiz");
          mylist.add("geeksforgeeks");
          mylist.add("quiz");
          mylist.add("practice");
          mylist.add("qa");
    
          System.out.println("Original List : \n" + mylist);
    
          Collections.shuffle(mylist);
    
          System.out.println("\nShuffled List : \n" + mylist);
      }
  }
  

  输出：

  Original List : 
  [ide, quiz, geeksforgeeks, quiz, practice, qa]
  
  Shuffled List : 
  [ide, practice, quiz, qa, geeksforgeeks, quiz]
  

• 使用用户提供的随机对象改组列表
  句法：

  Collections.shuffle(list, Random object);
  

  例子：

  // Java program to demonstrate working of shuffle()
  // with user provided source of randomness.
  import java.util.*;
    
  public class GFG {
      public static void main(String[] args)
      {
          ArrayList mylist = new ArrayList();
          mylist.add("ide");
          mylist.add("quiz");
          mylist.add("geeksforgeeks");
          mylist.add("quiz");
          mylist.add("practice");
          mylist.add("qa");
    
          System.out.println("Original List : \n" + mylist);
    
          // Here we use Random() to shuffle given list.
          Collections.shuffle(mylist, new Random());
          System.out.println("\nShuffled List with Random() : \n"
                             + mylist);
    
          // Here we use Random(3) to shuffle given list. Here 3
          // is seed value for Random.
          Collections.shuffle(mylist, new Random(3));
          System.out.println("\nShuffled List with Random(3) : \n"
                             + mylist);
    
          // Here we use Random(5) to shuffle given list.  Here 5
          // is seed value for Random.
          Collections.shuffle(mylist, new Random(5));
          System.out.println("\nShuffled List with Random(5) : \n"
                             + mylist);
      }
  }
  

  输出：

  Original List : 
  [ide, quiz, geeksforgeeks, quiz, practice, qa]
  
  Shuffled List with Random() : 
  [geeksforgeeks, practice, qa, ide, quiz, quiz]
  
  Shuffled List with Random(3) : 
  [quiz, ide, practice, quiz, geeksforgeeks, qa]
  
  Shuffled List with Random(5) : 
  [ide, quiz, geeksforgeeks, quiz, practice, qa]
  

• 如何编写我们自己的Shuffle方法?
  我们可以使用在O(n)时间内起作用的Fisher-Yates混洗算法。

  // Java Program to shuffle a given array
  import java.util.Random;
  import java.util.Arrays;
  public class ShuffleRand 
  {
      // A Function to generate a random permutation of arr[]
      static void randomize( int arr[], int n)
      {
          // Creating a object for Random class
          Random r = new Random();
             
          // Start from the last element and swap one by one. We don't
          // need to run for the first element that's why i > 0
          for (int i = n-1; i > 0; i--) {
                 
              // Pick a random index from 0 to i
              int j = r.nextInt(i);
                 
              // Swap arr[i] with the element at random index
              int temp = arr[i];
              arr[i] = arr[j];
              arr[j] = temp;
          }
    
          // Prints the random array
          System.out.println(Arrays.toString(arr));
      }
         
      // Driver Program to test above function
      public static void main(String[] args) 
      {         
           int[] arr = {1, 2, 3, 4, 5, 6, 7, 8};
           int n = arr.length;
           randomize (arr, n);
      }
  }
  

  输出：

  [5, 7, 1, 3, 6, 8, 4, 2]