How to solve a problem related with implementing Inheritance?

Question

Hello,
So i come on this way to ask for help about implementing Inheritance on my application. So the problem is:
I am making a Application which i need to capture audio and that analyze that capture by Spectrum Analyzer, Volumes etc.
And I will use several microphones in this application so i will use same code in capturing audio.
I have a class called Application which has the GUI and the events, like button events and update the values in the GUI. In my first version of the Application i had everything here but i don´t like that and is not good for the performance so i want to divide the code by other classes. Thats why i am trying the Inheritance.
So i created a class called Equipment which is the superclass and in this class will have the method captureAudio(), calculateRMSLevel(), sendOutPresenceUpdates() etc.. And i have 3 variables:
public abstract class Equipment {
    public AudioFormat format;
    public TargetDataLine line;
    public Mixer mixer;
    public EventListenerList listenerList = new EventListenerList();
    public Equipment(AudioFormat format, TargetDataLine line, Mixer mixer){
        this.format = format;
        this.line = line;
        this.mixer = mixer;
    public AudioFormat getFormat() {
        return format;
    public void setFormat(AudioFormat format) {
        this.format = format;
    public TargetDataLine getLine() {
        return line;
    public void setLine(TargetDataLine line) {
        this.line = line;
    public Mixer getMixer() {
        return mixer;
    public void setMixer(Mixer mixer) {
        this.mixer = mixer;
     public int calculateRMSLevel(byte[] audioData){
     // audioData might be buffered data read from a data line
        long lSum = 0;
        for(int i=0; i<audioData.length; i++)
            lSum = lSum + audioData;
double dAvg = lSum / audioData.length;
double sumMeanSquare = 0d;
for(int j=0; j<audioData.length; j++)
sumMeanSquare = sumMeanSquare + Math.pow(audioData[j] - dAvg, 2d);
double averageMeanSquare = sumMeanSquare / audioData.length;
return (int)(Math.pow(averageMeanSquare,0.5d) + 0.5);
public void sendOutPresenceUpdates(int FullJIDAndResource, String NewPresence) {
     Object[] listeners = listenerList.getListenerList();
     Integer inputValue = _FullJIDAndResource;
     String convertedValue = inputValue.toString();
// Empty out the listener list
     // Each listener occupies two elements - the first is the listener class and the second is the listener instance
for (int i=0; i < listeners.length; i+=2) {
          if (listeners[i]==CustomPresenceListener.class) {
               ((CustomPresenceListener)listeners[i+1]).presenceEventOccurred(new CustomPresenceEvent(this, convertedValue, _NewPresence));
public void listenForPresenceEvents(CustomPresenceListener _listener) {
          listenerList.add(CustomPresenceListener.class, _listener);
public void removeEventListener(CustomPresenceListener _listener) {
          listenerList.remove(CustomPresenceListener.class, _listener);
public void captureAudio(){
And i have questions about the constructor, is right the constructor that i created in the superclass?
So i create a subclass called Microphone1 and in this class i make override from the method captureAudio() from the superclass and here i create the thread for the capture.class Microphone1 extends Equipment{
public Microphone1(AudioFormat format, TargetDataLine line, Mixer mixer){
super(format,line,mixer);
public void captureAudio(){
try{
format = getFormat();
Mixer.Info[] mixerInfo =AudioSystem.getMixerInfo();
//DataLine.info get the information about the line.
DataLine.Info info = new DataLine.Info(TargetDataLine.class,format);
Mixer mixer = AudioSystem.getMixer(mixerInfo[3]);
// get the info from the desired line.
line = (TargetDataLine)AudioSystem.getLine(info);
//Get a TargetDataLine on the selected mixer.
line = (TargetDataLine) mixer.getLine(info);
line.open(format);
line.start();
CaptureThread captureThread = new CaptureThread();
captureThread.start();
} catch (Exception e) {
System.out.println(e);
System.exit(0);
}//end catch
But now i have a problem in the class Application, because i want to start the capture when i click in the button so i created the actionPerfomed and inside of this event i create this:Microphone1 m1 = new Microphone1(format,line,mixer);
m1.captureAudio();
But when i execute the application and click in the button appears this: java.lang.NullPointerException :/ and i don't know how to solve this.
Any help? Where i am wrong?                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   

Answer 1

Hello Kayaman,
Well thinking in that way is not good creating the Microphone1 object every time i click in the button.
So i put e.printStackTrace in the catch block the show me this error:
java.lang.NullPointerException
at com.sun.media.sound.Toolkit.isFullySpecifiedAudioFormat(Toolkit.java:137)
at com.sun.media.sound.AbstractDataLine.open(AbstractDataLine.java:98)
at com.sun.media.sound.AbstractDataLine.open(AbstractDataLine.java:139)
at App.Microphone1.captureAudio(Microphone1.java:42)
at App.Application.startBtnActionPerformed(Application.java:529)
at App.Application.access$000(Application.java:29)
at App.Application$1.actionPerformed(Application.java:152)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.java:6267)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
at java.awt.Component.processEvent(Component.java:6032)
at java.awt.Container.processEvent(Container.java:2041)
at java.awt.Component.dispatchEventImpl(Component.java:4630)
at java.awt.Container.dispatchEventImpl(Container.java:2099)
at java.awt.Component.dispatchEvent(Component.java:4460)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4577)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4238)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4168)
at java.awt.Container.dispatchEventImpl(Container.java:2085)
at java.awt.Window.dispatchEventImpl(Window.java:2478)
at java.awt.Component.dispatchEvent(Component.java:4460)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
at App.Microphone1.captureAudio(Microphone1.java:42):
This error is about this line: line.open(format);at App.Application.startBtnActionPerformed(Application.java:529): m1.captureAudio();:/