在Java中向BigDecimal添加BigDecimal

Question

我無法使其工作。我已經寫了筆記，希望能夠解釋我正在嘗試做什麼。控制檯在該行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

你得到這一點，因爲totalCost是空輸出錯誤，然後你想使用的對象，它的引用。

你應該做的是將這一行添加到你的類的構造函數。

totalCost = BigDecimal.ZERO;