8.12 Ch 8 Program: Playlist (Java) You will be building a linked list. Make sure
ID: 3859328 • Letter: 8
Question
8.12 Ch 8 Program: Playlist (Java)
You will be building a linked list. Make sure to keep track of both the head and tail nodes.
(1) Create two files to submit.
SongEntry.java - Class declaration
Playlist.java - Contains main() method
Build the SongEntry class per the following specifications. Note: Some methods can initially be method stubs (empty methods), to be completed in later steps.
Private fields
String uniqueID - Initialized to "none" in default constructor
string songName - Initialized to "none" in default constructor
string artistName - Initialized to "none" in default constructor
int songLength - Initialized to 0 in default constructor
SongEntry nextNode - Initialized to null in default constructor
Default constructor (1 pt)
Parameterized constructor (1 pt)
Public member methods
void insertAfter(SongEntry currNode) (1 pt)
void setNext(SongEntry nextNode) - Mutator (1 pt)
String getID()- Accessor
String getSongName() - Accessor
String getArtistName() - Accessor
int getSongLength() - Accessor
SongEntry getNext() - Accessor
void printPlaylistSongs()
Ex. of printPlaylistSongs output:
(2) In main(), prompt the user for the title of the playlist. (1 pt)
Ex:
(3) Implement the printMenu() method. printMenu() takes the playlist title as a parameter and a Scanner object, outputs a menu of options to manipulate the playlist, and reads the user menu selection. Each option is represented by a single character. Build and output the menu within the method.
If an invalid character is entered, continue to prompt for a valid choice. Hint: Implement Quit before implementing other options. Call printMenu() in the main() method. Continue to execute the menu until the user enters q to Quit. (3 pts)
Ex:
(4) Implement "Output full playlist" menu option. If the list is empty, output: Playlist is empty (3 pts)
Ex:
Ex (empty playlist):
(5) Implement the "Add song" menu item. New additions are added to the end of the list. (2 pts)
Ex:
(6) Implement the "Remove song" method. Prompt the user for the unique ID of the song to be removed.(4 pts)
Ex:
(7) Implement the "Change position of song" menu option. Prompt the user for the current position of the song and the desired new position. Valid new positions are 1 - n (the number of nodes). If the user enters a new position that is less than 1, move the node to the position 1 (the head). If the user enters a new position greater than n, move the node to position n (the tail). 6 cases will be tested:
Moving the head node (1 pt)
Moving the tail node (1 pt)
Moving a node to the head (1 pt)
Moving a node to the tail (1 pt)
Moving a node up the list (1 pt)
Moving a node down the list (1 pt)
Ex:
(8) Implement the "Output songs by specific artist" menu option. Prompt the user for the artist's name, and output the node's information, starting with the node's current position. (2 pt)
Ex:
(9) Implement the "Output total time of playlist" menu option. Output the sum of the time of the playlist's songs (in seconds). (2 pts)
Ex:
Explanation / Answer
package songs;
//Include packages.
import java.util.Scanner;
//Create the class Playlist with main() method.
public class Playlist
{
//Declare the objects.
public static Scanner sc = new Scanner(System.in);
public static Scanner scInt = new Scanner(System.in);
//Head node object of the SongEntry.
public static SongEntry headSong = new SongEntry();
//Tail node object of the SongEntry.
public static SongEntry tailSong = new SongEntry();
public static SongEntry allEntries;
public static int numberOfNodes = 0;
//printMenu() method to print the entire menu.
public static void printMenu(String playlistTitle)
{
//Print on the console.
System.out.println(" "+playlistTitle.toUpperCase()+" PLAYLIST MENU");
System.out.println("a - Add song d - Remove song c - Change position "
+ "of song s - Output songs by specific artist");
System.out.println("t - Output total time of playlist (in seconds) o "
+ "- Output full playlist q - Quit");
//prompt the user to enter the choice.
System.out.println(" Choose an option: ");
String option = sc.next();
//Check the choice.
boolean isEnter = option.equals("a") || option.equals("d") || option.equals("c")
|| option.equals("s") || option.equals("t")
|| option.equals("o") || option.equals("q");
//Valid choice.
if(isEnter)
{
//Start the switch-case
switch(option.charAt(0))
{
//Addsong.
case 'a': addSong();
printMenu(playlistTitle);
break;
//Remove song
case 'd': allEntries = removeSong(allEntries);
printMenu(playlistTitle);
break;
//Change the song position.
case 'c': allEntries = changeSongPosition(allEntries);
printMenu(playlistTitle);
break;
//Song by the specific artist.
case 's': songsBySpecificArtist(allEntries);
printMenu(playlistTitle);
break;
//Total time of the playlist.
case 't': totalTimeofPlaylist(allEntries);
printMenu(playlistTitle);
break;
//Output full playlist.
case 'o': outputFullPlaylist(allEntries);
printMenu(playlistTitle);
break;
//Quit
case 'q': break;
}
}
//Invalid choice.
else
{
System.out.println("Invalid Choice !");
printMenu(playlistTitle);
}
}
//outputFullPlaylist() method
public static void outputFullPlaylist(SongEntry entries)
{
int counter = 1;
//Playlist has certain songs.
if(entries != null)
{
System.out.println(counter+".");
// head node
entries.printPlaylistSongs();
counter++;
//Print the result.
while(entries.nextNode != null) // all the remaining nodes
{
entries = entries.nextNode;
System.out.println(counter+".");
entries.printPlaylistSongs();
counter++;
}
}
//Playlist is empty.
else
{
System.out.println("Playlist is empty");
}
}
//addSong() method
public static void addSong()
{
//Prompt the user to add all the details about the song.
sc = new Scanner(System.in);
System.out.println("ADD SONG");
System.out.println("Enter song's Unique ID: ");
String songID = sc.next();
sc = new Scanner(System.in);
System.out.println("Enter song's name: ");
String songname = sc.nextLine();
sc = new Scanner(System.in);
System.out.println("Enter artist's name: ");
String artistName = sc.nextLine();
System.out.println("Enter song's length(in seconds): ");
int songlength = scInt.nextInt();
SongEntry entry = new SongEntry(songID, songname, artistName, songlength);
//If all the Entries are null.
if(allEntries == null)
{
headSong = entry; // this is the head
allEntries = entry;
tailSong = entry; // this is the tail
numberOfNodes++;
}
//entries are present.
else
{
allEntries.insertAfter(entry);
tailSong = entry;
numberOfNodes++;
}
}
//removeSong() method
public static SongEntry removeSong(SongEntry entries)
{
//Prompt the user to enter the Song ID to be removed.
System.out.println("Enter the song's unique ID: ");
String id = sc.next();
SongEntry newEntry = null, entry=null;
int counter = 0;
//Run the while loop till the entries are null.
while(entries != null)
{
//if counter is not equal to zero.
if(counter!=0)
{
newEntry.nextNode = null;
newEntry = newEntry.nextNode;
}
if(!entries.getID().equals(id))
{
//Create an object of the SongEntry.
newEntry = new SongEntry();
newEntry.setUniqueID(entries.getID());
newEntry.setSongName(entries.getSongName());
newEntry.setArtistName(entries.getArtistName());
newEntry.setSongLength(entries.getSongLength());
if(entry == null)
entry = newEntry;
else
entry.insertAfter(newEntry);
counter++;
}
else
{
System.out.println(entries.getSongName()+" removed");
numberOfNodes--;
}
entries = entries.nextNode;
}
return entry;
}
//changeSongPosition() method.
public static SongEntry changeSongPosition(SongEntry entries)
{
//Prompt the user to enter the old and new song position.
System.out.println("CHANGE POSITION OF SONG");
System.out.println("ENTER song's current position: ");
int currentPos = scInt.nextInt();
System.out.println("Enter new position of song: ");
int newPos = scInt.nextInt();
SongEntry currentPosEntry = null, entry = null, newPosEntry = null, returnEntry = null;
entry = entries;
int counter = 1;
// If new position is -1, set it to 1.
if(newPos<1)
newPos = 1;
//If the new position is more than the total number of songs
else if(newPos>numberOfNodes)
//Set the new position to the total number of nodes.
newPos = numberOfNodes;
System.out.println("cuurent pos: "+currentPos);
System.out.println("new pos: "+newPos);
//Run the for loop to change the position.
for(int i=1; i<=numberOfNodes; i++)
{
if(i==currentPos)
currentPosEntry = entries;
else if(i==newPos)
newPosEntry = entries;
else
entries = entries.nextNode;
}
entries = entry;
//Run the for loop to adjust the current position.
while(counter <= numberOfNodes+1)
{
if(counter == currentPos) //need to adjust the current position
{
entries = entries.nextNode;
if(entries !=null)
{
entry = new SongEntry(entries.getID(), entries.getSongName(),
entries.getArtistName(), entries.getSongLength());
if(returnEntry == null)
returnEntry = entry;
else
returnEntry.insertAfter(entry);
entries = entries.nextNode;
}
counter++;
}
else if(counter == newPos)
{
entry = currentPosEntry;
entry.nextNode = null;
if(returnEntry == null)
returnEntry = entry;
else
returnEntry.insertAfter(entry);
counter++;
}
else
{
if(entries !=null)
{
entry = new SongEntry(entries.getID(), entries.getSongName(),
entries.getArtistName(), entries.getSongLength());
if(returnEntry == null)
returnEntry = entry;
else
returnEntry.insertAfter(entry);
entries = entries.nextNode;
}
counter++;
}
}
return returnEntry;
}
//totalTimeofPlaylist() method
public static void totalTimeofPlaylist(SongEntry entries)
{
System.out.println("OUTPUT TOTAL TIME OF PLAYLIST (IN SECONDS)");
int totalSeconds = entries.getSongLength();
entries = entries.nextNode;
//Run the while loop to calculate the toatl song length.
while(entries != null)
{
totalSeconds += entries.getSongLength();
entries = entries.nextNode;
}
System.out.println("Total Time: "+totalSeconds+" seconds");
}
//songsBySpecificArtist() method
public static void songsBySpecificArtist(SongEntry entries)
{
sc = new Scanner(System.in);
System.out.println("OUTPUT SONGS BY SPECIFIC ARTIST");
//Prompt the user to enter the artist name.
System.out.println("Enter artist's name: ");
String artistname = sc.nextLine();
//Print till the song entries are not null.
while(entries != null)
{
if(entries.getArtistName().equals(artistname))
{
entries.printPlaylistSongs();
}
entries = entries.nextNode;
}
}
/**
* @param args
*/
//main() method
public static void main(String[] args)
{
//Prompt the user to enter the playlist title.
System.out.println("Enter playlist's title: ");
sc = new Scanner(System.in);
String title = sc.nextLine();
//Call the printMenu() method.
printMenu(title);
}
}
//SongEntry.java
package songs;
//Create the class SongEntry
public class SongEntry
{
//Declare private data members.
private String uniqueID;
private String songName;
private String artistName;
private int songLength;
SongEntry nextNode;
//Default constructor.
SongEntry()
{
uniqueID = "";
songName = "";
artistName = "";
songLength = 0;
nextNode = null;
}
//Parameterized constructor
SongEntry(String uniqueID, String songName, String artistName, int songLength)
{
this.uniqueID = uniqueID;
this.songName = songName;
this.songLength = songLength;
this.artistName = artistName;
this.nextNode = null;
}
//insertAfter() method to insert songs in the linked list.
public void insertAfter( SongEntry entry)
{
SongEntry entries = this;
while(entries.nextNode != null)
{
entries = entries.nextNode;
}
entries.nextNode = entry;
}
//setNext() method to return the nextNode.
public void setNext(SongEntry entry){
this.nextNode = entry;
}
//getID() method to return the unique ID
public String getID()
{
return this.uniqueID;
}
//getSongName() method to return the songName.
public String getSongName()
{
return this.songName;
}
//getArtistName() method to return the artistName.
public String getArtistName()
{
return this.artistName;
}
//getSongLength() method to return the songLength
public int getSongLength()
{
return this.songLength;
}
//getNext() method to return the nextNode.
public SongEntry getNext()
{
return this.nextNode;
}
//setUniqueID() to set the unique ID.
public void setUniqueID(String uniqueID)
{
this.uniqueID = uniqueID;
}
//setSongName() method to set the SongName.
public void setSongName(String songName)
{
this.songName=songName;
}
//setArtistName() to set the artist name.
public void setArtistName(String artistName)
{
this.artistName=artistName;
}
//setSongLength() method to return the songLength.
public void setSongLength(int songLength )
{
this.songLength=songLength;
}
//printPlaylistSongs() method to print the results.
public void printPlaylistSongs()
{
System.out.println("Unique ID: "+getID());
System.out.println("Song Name: "+getSongName());
System.out.println("Artist Name: "+getArtistName());
System.out.println("Song Length(in seconds): "+getSongLength());
}
}
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