java - 创建一个每次调用时打印数组列表的不同随机条目的方法？

Question

我正在制作一个模拟媒体播放器程序，允许用户输入、编辑、删除和查看所有轨道。很基本，我知道。但是我想添加一个功能，允许每次选择“播放随机歌曲”时打印数组列表中的随机条目以模拟音乐播放器的随机播放功能。
所以我的方法会像

public void playRandom()

{
System.out.println("Now Playing: " + *insert code here?* ")
} 

我有 3 个数组列表，分别代表轨道名称、轨道年份和轨道艺术家，但是当我打印到屏幕时，我希望它以这样一种方式显示:先打印艺术家，然后是连字符，然后是轨道名称？

我的代码如下:

我的主要类(class):
包 ca1;

//imports the Random mechanism
  import java.util.Random;

//imports the scanner
  import java.util.Scanner;


public class MainClass extends UserInput {

        public String nextInt;

        public static void main(String[] args) {

      //Links to the UserInput class to create an object that stores
      //user input    
        UserInput ui = new UserInput();

      //Creates new scanner object
        Scanner input = new Scanner(System.in);

      //Declares the int "opt" so it can be used in the menu  
        int opt;



        //Calls Methods Class so methods can be used below
        Methods methodsFunctions = new Methods();


        //initial prompt only displayed when program is first ran
        System.out.println("Welcome to your music library");


        //Usig a do while loop so that the program keeps running until 
        //a specific condition is met, in this case it's when 0 is selected.
        do 
        {

          //Menu Prompts printed to the screen for the user to select from
            System.out.println("........ \n");
            System.out.println("Press 0 to Exit\n");
            System.out.println("Press 1 to Add a Song\n");
            System.out.println("Press 2 to View All Songs\n");
            System.out.println("Press 3 to Remove a Song\n");
            System.out.println("Press 4 to Edit Song Information\n");
            System.out.println("Press 5 to Play Random Song\n");
            System.out.println("Press 6 to Delete All Songs\n");

          //Monitors the next Int the user types
            opt = input.nextInt();





            //"if" statements
            if (opt == 0) 
            {
            //This corresponds to the condition of the while loop,      
            //The program will exit and print "Goodbye!" for the user.  

             System.out.println("Goodbye!");  
            } 


            else if (opt == 1)                 
            { 
             //This method allows the user to add a song to the library.
             //With the format being Title, Artist, Year.

               methodsFunctions.addEntry();
            }




            else if (opt == 2)
            {
              //This method prints the contents of the Array List to the screen  

                methodsFunctions.viewAll(); 
            } 




            else if (opt == 3)             
            {
              //This method allows the user to remove an indiviual song from
              //their music library  

                methodsFunctions.removeOne(); 
            } 



            else if (opt == 4) 
            {
              //This method allows the user to edit the data of a particular 
              //and then prints the new value on screen

                methodsFunctions.editItem();
            } 


            else if (opt == 5) 
            {    
               //This method will print out "Now playing" followed by a random
               //song to simulate a music player's shuffle effect.


                //methodsFunctions.RandomSong();
                System.out.println("Now Playing ");
            } 



            else if (opt == 6) 
            {
                //This method will clear all contents of the library.
                //It will ask the user to confirm their choice.

                methodsFunctions.clearAll();
             } 



            else 
            {
              //If the user selects an incorrect number, the console will 
              //tell the user to try again and the main menu will print again

                System.out.println("Incorrect Entry, please try again");
            }


        } //do-while loop
        while (opt > 0);

    }
}

我的方法类:

package ca1;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.Scanner;

public class Methods extends UserInput

{
 Scanner input = new Scanner (System.in);

 //Declare array lists  
 List<String> songName = new ArrayList<>();
 List<String> songArtist = new ArrayList<>();
 List<Integer> songYear = new ArrayList<>();

    UserInput ui = new UserInput();

    private Random newRandom;


            public void clearAll(){  
            System.out.println("Are you sure?");
            System.out.print("1: Yes \n2: No" + "\n");
            System.out.print("");

            int confirmDelete=input.nextInt();
            if (confirmDelete == 1){
            songName.clear();
            songYear.clear();
            System.out.println("Your music library has been cleared");
        }   

}

        public void viewAll(){  
        System.out.println("\n");
        for (int i = 0; i < songName.size(); i++){
        int counter=i+1;
        System.out.println(counter+": "+songArtist.get(i)+" - "+ songName.get(i)+ " ("     +songYear.get(i)+") ");
        }
        System.out.println("\n");
}   

    public void addEntry(){
    //System.out.print("Enter Name: ");
    String newName = ui.getString("Enter the name of the track");
    songName.add(newName);
    String newArtist = ui.getString("Who performs this track");
    songArtist.add(newArtist);
    System.out.print("What year was the track released? ");
    int newYear=input.nextInt();
    songYear.add(newYear);

    System.out.println("\n" + "Thank you, " +songName.get(songName.size()-1) + " has been   added to the library.");
    System.out.println("\n" + "Press 2 to view your library." + "\n");


    /*
    System.out.println("\n"+songName.get(songName.size()-1));
    System.out.println("\n"+songArtist.get(songArtist.size()-1));
    System.out.println("\n"+songYear.get(songYear.size()-1));
    */
} 

 public void removeOne(){       

    System.out.println(" Which song would you like to delete? (1 to "+songName.size()+")");
    viewAll();
    int remove=input.nextInt();
    if (remove >songName.size()){
        System.out.println("Invalid ");
    }
    else {
        remove--;
        System.out.println("Are you sure you would like to delete  "+songArtist.get(remove)+" - "+songName.get(remove)+" (" +songYear.get(remove)+ ") from your music library?");
        System.out.print("1: Yes \n2: No" + "\n");
        int confirmDelete=input.nextInt();
        if (confirmDelete == 1){
            songArtist.remove(remove); 
            songName.remove(remove);
            songYear.remove(remove);
            System.out.println(songName.get(remove)+ " has just been removed from your  music library");
            // viewAll();
        }       
    }
} 


   public void playRandom()
   {
      String RandomSong = (SongName.random);


       System.out("Now playing + " RandomSong);

   }            


 public void editItem(){
    viewAll();
    System.out.println("Choose the song you want to edit (1 to "+songName.size()+")");
  //prints out the contents of library with first entry being index 1
  //The library is numbered and goes as far as the index of the last entry  

    int edit=input.nextInt();       
    if (edit >songName.size()){
        System.out.println("Invalid Selection");

      //if user selects a number that corresponds to an index that's not
      //In the array list, they will be shown an error.
    }



        else{
        edit--;
        System.out.println("\n" + "Enter New Track Name: ");
        input.nextLine();
        String editName=input.nextLine();
        songName.set(edit,editName);
      //Edits the songName value of the Song object selected 

        System.out.println("\n" + "Enter New Artist ");
        String editArtist=input.nextLine();
        songArtist.set(edit,editArtist);
      //Edits the songArtist value of the Song object selected 


        System.out.println("\n" + "Enter New Year:");
        int editYear;
        editYear = input.nextInt();
        songYear.set(edit,editYear);
      //Edits the songName value of the Song object selected

        System.out.print("\n" + "Your changes have been saved:" + "\n");
        System.out.print("\n" + "This is your current library");
        viewAll();
    }
}


}  

Answer 1

好吧，我认为你必须做这样的事情:

找出您的阵列有多长。例如，50 首歌曲。然后，生成一个介于 0 和 length-1 之间的随机数。

public void playRandom()
{
  int randomnumber =(int)(Math.random() * (length-1));
  System.out.println("Now Playing: " + arrayOfSongName[randomnumber]);
} 

然后你有一个随机轨道。