How to decompiling Java APK file

Question

I have a apk file that I want to decompile.I tried Smali2Java , and apktool but when I check the decompiled files, all of them contain only the definitions of the variables and functions. For example :

<code>


import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.app.Service;
import android.os.PowerManager;
import android.app.Notification;
import android.os.IBinder;

public class VoiceService extends Service {
    private final md a;
    private boolean b;
    private PowerManager.WakeLock c;
    private static final Object d;
    private long e;
    private String f;
    private PowerManager.WakeLock g;
    private final BroadcastReceiver h;
    private static final String[] z;

    static {
    }

    public int onStartCommand(Intent p1, int p2, int p3);


    class VoiceService$2 extends BroadcastReceiver {
        final VoiceService a;
    }
}

</code>

what is the problem? Thanks