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java code compile but didn't work


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Hello everyone,

 

today I test code from Head First Java book about Jukebox3

 

(if you have this book please see on page : 537 this is code about Jukebox3, and on page 550 about class Song implements Comparable<Song> chapter 16 about collection and data Structure)

 

this the code about Jukebox3 :

 import  java.util.*; import  java.io.*;    public class Jukebox3 {         ArrayList<Song> songList = new ArrayList<Song>();	  	  public static void main(String[] args) {	    new Jukebox3().go();		}			  void go() {	     getSongs();		 System.out.println(songList);		 Collections.sort(songList);		 System.out.println(songList);		 }		 	  void getSongs() {	     try {		   File file = new File("src/SongList.txt");		   BufferedReader reader = new BufferedReader(new FileReader(file));		   String line = null;		   while((line = reader.readLine())!=null) {		      addSong(line);		   } // close while		 		 } catch(Exception ex) {		 ex.printStackTrace();		 }		} //close getSongs			   void addSong(String lineToParse) {	     String[] tokens = lineToParse.split("/");		 Song nextSong = new Song(tokens[0], tokens[1], tokens[2], tokens[3]);		 songList.add(nextSong);		} // close addSong	} // closing class					

and this code about class Song implements Comparable<Song> :

  class Song implements Comparable<Song> {    String title;	String artist;	String rating;	String bpm;		public int compareTo(Song s) {		return title.compareTo(s.getTitle());	}		Song(String t, String a, String r, String  {	  title = t;	  artist = a;	  rating = r;	  bpm = b;	}		public String getTitle() {	  return title;	 }	 	 public String getArtist() {	  return artist;	 }	 	 public String getRating() {	  return rating;	 }	 	 public String getBpm() {	  return bpm;	 }	 	 public String toString() {	  return title;	 }	} // closing class

both of this code able to compile,

 

but when I run it's shown message :

 

java.lang.ArrayIndexOutOfBoundsException: 2
at Jukebox3.addSong(Jukebox3.java:35)
at Jukebox3.getSongs(Jukebox3.java:25)
at Jukebox3.go(Jukebox3.java:13)
at Jukebox3.main(Jukebox3.java:9)
[]
[]
Q : Why this code can be compile but when I run this code, it shown like on above?
whereas, on Head First Java this code can be run well
please help me
Thanks
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It says ArrayIndexOutOfBounds, which means that one of the indices is too high or negative.

It's probably happening on this line:

Song nextSong = new Song(tokens[0], tokens[1], tokens[2], tokens[3]);

Since the array is being created by splitting a string then you have to check that the string is formed correctly. The strings are coming from src/SongList.txt so check the contents of that file. Show it here.

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I had delete src/SongList.txt, and change it to : File file = new File("SongList.txt"); but the result :

 

java.io.FileNotFoundException: SongList.txt (The system cannot find the file specified)
at java.io.FileInputStream.open(Native Method)
at java.io.FileInputStream.<init>(Unknown Source)
at java.io.FileReader.<init>(Unknown Source)
at Jukebox3.getSongs(Jukebox3.java:22)
at Jukebox3.go(Jukebox3.java:13)
at Jukebox3.main(Jukebox3.java:9)
[]
[]
and about line :
Song nextSong = new Song(tokens[0], tokens[1], tokens[2], tokens[3]);

when I delete or add the one of array for instance : I delete tokens[3] or I add token[4] it won't compile.

 

Q : how to write directory path on File file = new File("SongList.txt"); so, that java .io able to find SongList.txt without using "src/SongList.txt"?

 

please answer

 

thanks

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If the file is in the src folder, then you need to put that in the path. You need to give it the correct path, you can't point it to a file that doesn't exist. Either move the file or give it the correct path, that should be obvious.

 

 

 

Why this code can be compile but when I run this code, it shown like on above?

Array indexes like that cannot be checked at compile time. You are seeing a run-time error, not a compile-time error. It is your responsibility as a programmer to make sure that the array indexes exist before you try to use them.

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