Adding a BigDecimal to BigDecimal in Java [closed]

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I can't get this to work. I have written notes that will hopefully explain what I'm attempting to do. The console outputs an error at the line totalCost = totalCost.add(new BigDecimal(result));

private void btn_motherboardActionPerformed(java.awt.event.ActionEvent evt) {                                                

    String cost = cb_motherboard.getSelectedItem().toString();
    //gets item from combobox. Makes a string
    Components.addElement(cost);// adds string to model
    lb_computer_components.setModel(Components);//sets model to jlist

    String result = cost.substring(cost.lastIndexOf('£') + 1);
    //creates a substring containing information after £ (for example 45.99)

    totalCost = totalCost.add(new BigDecimal(result));
    //totalcost is a public bigdecimal, i want to add 45.99 to it in this example

    String BD = totalCost.toString();
    //change the new totalcost to a string

    String stringTotal = n.format(BD);
    //format that string to a currency

    txt_total_computer.setText(stringTotal); 
    //output that string to a textfield

}        

Answer 1

You're getting this because totalCost is null, and then you're trying to use the object that it references.

What you should do is add this line to your class's constructor.

totalCost = BigDecimal.ZERO;