我无法让这个工作。我写了笔记,希望能够解释我正在尝试做什么。控制台在行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
}
答案 0 :(得分:0)
你得到这个是因为totalCost
为空,然后你试图使用它引用的对象。
你应该做的是将这一行添加到你的类的构造函数中。
totalCost = BigDecimal.ZERO;