I am new to programming and trying to insert the mp3 file on Mac, but I have errors with these codes. I have been looking for solutions for a long time but I was not able to find the right answers. I would like to know what I did wrong.

import javazoom.jl.player.Player;
import java.io.BufferedInputStream;
import java.io.FileInputStream;

public class Music {

    public static void main(String [] args) {

        String filename = "src_music_typing.mp3";
        MusicPlayer music = new MusicPlayer(filename);
        music.play();
    }
}

class MusicPlayer {

    private final String mp3File;

    private Player jlPlayer;

    public MusicPlayer(String mp3File) {
        this.mp3File = mp3File;
    }

    public void play() {
        try {
            FileInputStream fis = new FileInputStream(mp3File);
            BufferedInputStream bis = new BufferedInputStream(fis);
            jlPlayer = new Player(bis);
        } catch (Exception e) {
            System.out.println("problem file is "   mp3File);
            System.out.println(e.getMessage());
        }
        new Thread() {
            public void run() {
                try {
                    jlPlayer.play();
                } catch (Exception e) {
                    System.out.println(e.getMessage());
                }
            }
        }.start();
    }
    public void close() {
        if(jlPlayer != null) jlPlayer.close();
    }
}

Problem:

problem file is src_music_typing.mp3

src_music_typing.mp3 (No such file or directory)

Cannot invoke "javazoom.jl.player.Player.play()" because "this.this$0.jlPlayer" is null

CodePudding user response：

The error is telling you simply that src_music_typing.mp3 does not exist; evidently you aren't running this in the directory you think you're running it in. Trivial solution: Make that path string (String filename = "src_...") an absolute path instead.

NB: It's a cavalcade of problems, here. Your code is bad and it leads to inefficient error messages. Inefficient enough to confuse you, for example.

You should never catch an exception just to log it and then blindly continue; I know a ton of code snippets do this, but that part of them is just bad. You don't want to do that - dealing with an error by blindly continuing on is, obviously, a really silly thing to do!

The right way to deal with exceptions that you don't explicitly know how to handle is instead to just throw them on. your play method should be declared as throws IOException, as this is inherent to your API design, this is fine (it's inherent because your music player class as a property that represents a file name, and anything file related is expected to throw IOExceptions, hence, fine - not leaking an abstraction).

Then the whole try/catch bit can just go away, yay! Your code is better and shorter and easier to understand, win win win!

Because you didn't do that, and you just run blindly on, you get a second error that is complaining about attempting to invoke play() on a null pointer. This error is meaningless, in that it's merely a symptom, not the cause. The cause is the first error message. This is one of a few key reasons why 'keep blindly going' is a really bad idea - it means you get a ton of meaningless, confusing errors after the actual problem, resulting in a ton of error output, most of which is just hiding the actual problem.

If you can't throw them on, a distant second best solution is to put this in your catch blocks: throw new RuntimeException("uncaught", e);. This preserves all error information (type, message, stack trace, causal chain - all of it), and still ensures code does not blindly continue when your method is an unknown (to you) state. If you have an IDE that inserts catch blocks for you, update its template.

NB: main can and usually should be declared as static void main(String[] args) throws Exception {.