How can I add values from textfield when i press the button with not having all of the values

Question

im working on a java program using GUI, and i ran into a problem whenever i try to add the values from the text fields and one is missing it doesn't work and i get an error but if all of them are available i get the right answer, how can i add without having all the values?

JButton btnCheckOut = new JButton("CHECK OUT");
btnCheckOut.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent arg0) {
        double apples, strawberries, watermelon, tomatoe, carrot, beef, lamb, payment;

        apples = Double.parseDouble(textField.getText());
        strawberries = Double.parseDouble(textField_1.getText());
        watermelon = Double.parseDouble(textField_2.getText());
        tomatoe = Double.parseDouble(textField_3.getText());
        carrot = Double.parseDouble(textField_4.getText());
        beef = Double.parseDouble(textField_5.getText());
        lamb = Double.parseDouble(textField_6.getText());

        payment = (apples*8)+(strawberries*10)+(watermelon*14)+
                (tomatoe*5)+(carrot*6)+(beef*25)+(lamb*20);

        DecimalFormat df = new DecimalFormat("###.##");

       textField_7.setText(String.valueOf(df.format(payment)));


    }
});

Answer 1

Create an IF statement that sets the variables to zero if its respective TextField is empty, before you do the math operation.

if(textfield.getText().isEmpty())
{
    apples = 0;
}

Answer 2

When you make your textFields, initialize the text there to 0. Like

JTextField textField_1 = new JTextField("0");

Or, you could add

if(textField.getText() == ""){
   textField.setText("0");
}

For each text field before trying to parse to double.

Answer 3

Create eg getDoubleValue, which you apply to all your items when read. Simple as:

apples = getDoubleValue( textField.getText() );
...
...

then

public double getDoubleValue( String txt ) {
  double d = 0d;
  try {
    if( txt != null && !txt.isEmpty() ) {
      d = Double.parseDouble( txt );
    }
  } catch(Exception ex) {}
  return d;
}

(This will also take care for "dirty input", if the textfield does not contain a number it will set it to zero during parse).