I don't know what's wrong with the code. Can you guys help me out?

```
int a = Integer.parseInt(aTextField.getText());
int b = Integer.parseInt(bTextField.getText());
int c = Integer.parseInt(cTextField.getText());
int discriminant = (int)Math.pow((double)b, 2) - 4*a*c;
int x1 = (int)(-b + (double)Math.sqrt(discriminant) / 2*a);
int x2 = (int)(-b - (double)Math.sqrt(discriminant) / 2*a);

public DiscriminantSoft(){
    super("Quadratic Equation");
    setLayout(new FlowLayout());

    headerLabel = new JLabel("ax^2 + bx + c = 0");
    headerLabel.setToolTipText("You have to write a, b and c in order to calculate discriminant.");
    add(headerLabel);

    aTextField = new JTextField(3);
    add(aTextField);
    bTextField = new JTextField(3);
    add(bTextField);
    cTextField = new JTextField(3);
    add(cTextField);

    thehandler handler = new thehandler();
    aTextField.addActionListener(handler);
    bTextField.addActionListener(handler);
    cTextField.addActionListener(handler);

}

private class thehandler implements ActionListener{

    public void actionPerformed(ActionEvent event){
        String string = "";

        if(discriminant == 0){
                string=String.format("Discriminant: " +discriminant +" x: " +x1, event.getActionCommand());
        }
        else if(discriminant > 0){
            string=String.format("Discriminant: " +discriminant +" x: " +x1 +" x2: " +x2, event.getActionCommand());
        }
        else if(discriminant < 0){
            string=String.format("Discriminant is under zero! No x found", event.getActionCommand());
        }

        JOptionPane.showMessageDialog(null, string);
    }

}

```

> 
> Exception in thread "main" java.lang.NullPointerException
>  at DiscriminantSoft.(DiscriminantSoft.java:17)
>  at tuna.main(tuna.java:5)
> 
> 
> 

int a = Integer.parseInt(aTextField.getText()); is 17th row