Why, when calling a method, does it say that I need to catch an exception when I have already caught it?

Question

I have a class that loops some audio:

public class PlayGameMusic {
    public static void main(String[] args) throws Exception {
        try{
            AudioInputStream inputStream = AudioSystem.getAudioInputStream(new File("\\Users\\natal\\Desktop\\programs\\APCS\\Fill the Boxes.wav"));
            Clip clip = AudioSystem.getClip();
            clip.open(inputStream);
            clip.loop(Clip.LOOP_CONTINUOUSLY);
            Thread.sleep(10000);
        }
        catch(IOException error){System.out.println("IO Exception Error");}
        catch(InterruptedException error){System.out.println("InterruptedException");}
        catch(Exception error){System.out.print("System.out.println("Exception");");}
     }
}

I can compile this method and the compiler does not report any errors (I have tested this with print statements). However, when I try to call the main method of the above class (PlayGameMusic) in another class...

public class RunGame
{
    public static void main(String[] args)
    {
       PlayGameMusic.main(null);
    }
}

...I get this compiler error:

unreported exception java.lang.Exception; must be caught or declared to be thrown

I am catching the possible exceptions and the PlayGameMusic class works when run on its own. Why can't I call it from another class?

What does this do: `public static void main(String[] args) throws Exception {`, the `throws Exception` part? — Hovercraft Full Of Eels, Jun 08 '18 at 00:27
Sorry but this cannot compile: catch(Exception error){System.out.print("System.out.println("Exception");");} — lohnns, Jun 08 '18 at 00:38
`catch(IOException error){System.out.println("IO Exception Error");}` BTW - that should logically be `catch(IOException error){System.err.println("IO Exception Error");}` or even better (and shorter) `catch(IOException error){error.printStackTrace();}` — Andrew Thompson, Jun 08 '18 at 10:08

score 6 · Accepted Answer · answered Jun 08 '18 at 00:29

You've declared your main in PlayGameMusic to throw Exception. Even if nothing in that method actually throws Exception out of the method, you must catch it or declare it in a calling method, e.g. RunGame.main.

Because you are catching the exceptions in PlayGameMusic.main, you don't need to declare that it throws anything. In PlayGameMusic, change:

public static void main(String[] args) throws Exception

to

public static void main(String[] args)

score 1 · Answer 2 · answered Jun 08 '18 at 02:54

If a method calls another method which explicitly throws Exception, then the calling method should catch that Exception or declared it to be thrown in its own method signature

https://docs.oracle.com/cd/A97339_01/doc/bc4j/BC4JRuntimeFiles/obcExceptions.htm

score 0 · Answer 3 · answered Jun 08 '18 at 00:29

0

If PlayGameMusic.main can't throw Exception it shouldn't be declared with throw Exception. It shouldn't have throw Exception just because it can generate and catch Exception.

answered Jun 08 '18 at 00:29

Erik Levin

47
1
4

Why, when calling a method, does it say that I need to catch an exception when I have already caught it?

3 Answers3