Java 确定是否选择了哪个 JRadioButton

Question

我知道在Java中的事件驱动程序中可以找出哪个对象引起了事件(例如选择了JRadioButton，因此将发生特定的操作)。我的问题是，如果按钮组中有 2 个 JRadioButton，并且都添加了操作监听器，并且您不断从一个到另一个进行选择，是否可以找出 JRadioButton 之前被选择过吗？换句话说，如果我选择了另一个 JRadioButton，是否可以编写代码来确定在选择当前 JRadioButton 之前先前选择了哪个 JRadioButton？

public class Drinks extends JPanel implements ActionListener{
double drinksPrice = 2.10;
double noDrinks = 0;
static  String selectedDrink;
JRadioButton btnPepsi = new JRadioButton("Pepsi"); //add a button to choose different drinks

JRadioButton btnMtDew = new JRadioButton("Mt Dew"); 

JRadioButton btnDietPepsi= new JRadioButton("Diet Pepsi");

JRadioButton btnCoffee = new JRadioButton("Coffee");

JRadioButton btnTea = new JRadioButton("Tea");

JRadioButton btnNone = new JRadioButton("None");
JLabel lblDrinksHeading = new JLabel("Choose a drink (each drink is $2.10):");
ButtonGroup drinksButtonGroup = new ButtonGroup();



private static final long serialVersionUID = 1L;

public Drinks(){

    setLayout(new FlowLayout());    //Using GridLayout  

    btnPepsi.setActionCommand(btnPepsi.getText());    //set the ActionCommand to getText so I can retrieve the name for the receipt

    btnMtDew.setActionCommand(btnMtDew.getText());

    btnDietPepsi.setActionCommand(btnDietPepsi.getText());

    btnCoffee.setActionCommand(btnCoffee.getText());

    btnTea.setActionCommand(btnTea.getText());

    btnNone.setActionCommand(btnNone.getText());

    drinksButtonGroup.add(btnPepsi);
    drinksButtonGroup.add(btnMtDew);
    drinksButtonGroup.add(btnDietPepsi);
    drinksButtonGroup.add(btnCoffee);
    drinksButtonGroup.add(btnTea);
    drinksButtonGroup.add(btnNone);
    btnNone.setSelected(true); //set default to "none"

    btnPepsi.addActionListener(this);
    btnMtDew.addActionListener(this);
    btnDietPepsi.addActionListener(this);
    btnCoffee.addActionListener(this);
    btnTea.addActionListener(this);
    btnNone.addActionListener(this);

    add(lblDrinksHeading);

    add(btnPepsi);

    add(btnDietPepsi);

    add(btnMtDew);

    add(btnCoffee);

    add(btnTea);

    add(btnNone);


    repaint();
    revalidate();

    selectedDrink = drinksButtonGroup.getSelection().getActionCommand();
//add the drink price to totalPrice, it is adding it every time though, even if its none
/*if(drinksButtonGroup.getSelection() == btnNone){
    MenuFrame.totalPrice += 0;
    }
    else{
        MenuFrame.totalPrice += drinksPrice;
        }
*/


//      buttonGroup1.getSelection().getActionCommand()

//String selectedDrink = drinksButtonGroup.getSelection().toString();
//class 

}

@Override
public void actionPerformed(ActionEvent e) {

    Object source = e.getSource();

    if(source == btnNone) {

        MenuFrame.totalPrice += 0;
        TaxAndGratuityFrame.subtotalTextField.setText("$" + MenuFrame.totalPrice);
        TaxAndGratuityFrame.subtotalVariable = MenuFrame.totalPrice;
        TaxAndGratuityFrame.taxVariable = TaxAndGratuityFrame.subtotalVariable * TaxAndGratuityFrame.TAX_RATE;
        TaxAndGratuityFrame.taxTextField.setText("$" + TaxAndGratuityFrame.taxVariable);
        Receipt.receiptTotal.setText("Total: $" + (MenuFrame.totalPrice));
        Receipt.receiptsubtotal.setText("Subtotal: " + (TaxAndGratuityFrame.subtotalVariable));

    }

    else {

        MenuFrame.totalPrice += drinksPrice;
        TaxAndGratuityFrame.subtotalTextField.setText("$" + MenuFrame.totalPrice);
        TaxAndGratuityFrame.subtotalVariable = MenuFrame.totalPrice;
        TaxAndGratuityFrame.taxVariable = TaxAndGratuityFrame.subtotalVariable * TaxAndGratuityFrame.TAX_RATE;
        TaxAndGratuityFrame.taxTextField.setText("$" + TaxAndGratuityFrame.taxVariable);
        Receipt.receiptTotal.setText("Total: $" + (MenuFrame.totalPrice));
        Receipt.receiptsubtotal.setText("Subtotal: " + (TaxAndGratuityFrame.subtotalVariable));

    }

}

编辑:我会更具体。我正在创建一个“想象的”餐厅程序。在其中，我列出了几种价格相同的饮料(例如百事可乐:2.10 美元，Mountain Due:2.10 美元等)。这些列出的饮料是 JRadioButtons。一旦客户点击其中一个按钮“点一杯饮料”，2.10 美元将被添加到“总计”变量中。然而，当用户想要更换那里的饮料时，就会出现问题，因为如果他们单击不同的 JRadioButton，$2.10 仍将添加到“total”变量中。我想让他们可以更换那里的饮料，而无需每次在订单中添加 2.10 美元。

Answer 1

我认为问题出在这一行:

MenuFrame.totalPrice += drinksPrice;

因为“+=”将一个值增加另一个值，而不是简单地将两个值相加。

因此，每次用户单击其中一个单选按钮时，它都会不断地将 2.10 添加到您的总值(value)中，而如果您只是说:

MenuFrame.totalPrice = MenuFrame.totalPrice + drinksPrice;

它会将您的总价设置为当前总价加上饮料价格，而不是每次按下按钮时为总价加上 2.10。