我是初学者并试图制作一个简单的计算器。我已经搜索了其他答案，但我的问题是，在按下操作符后，它只保留第一个字符串
public class CalculatorFrame extends JFrame {
public CalculatorFrame(){
this.setTitle("Calculator");
this.setLayout(new BorderLayout(2,2));
MenuBar menuBar = new MenuBar();
JTextArea txtArea = new JTextArea();
txtArea.setEditable(false);
txtArea.setComponentOrientation(ComponentOrientation.RIGHT_TO_LEFT);
txtArea.setText("0");
txtArea.setFont(new Font("Sans Serif", Font.PLAIN,30));
JPanel panel = new JPanel();
panel.setLayout(new GridLayout(4,3,2,2));
JPanel panel2 = new JPanel();
panel2.setLayout(new GridLayout(6,1,2,2));
MyActionListener al = new MyActionListener(txtArea);
MyOperatorListener ol = new MyOperatorListener(txtArea);
JButton btn = new JButton();
int k=10;
for (int i=0; i<3; i++) {
k=k-3;
for (int j=0; j<3; j++) {
btn = new JButton(Integer.toString(k++));
btn.setPreferredSize(new Dimension(70, 60));
btn.setBackground(new Color(224,224,224));
btn.setBorder(BorderFactory.createRaisedSoftBevelBorder());
btn.setFont(new Font("Sans Serif", Font.BOLD,20));
btn.addActionListener(al);
panel.add(btn);
}
k=k-3;
}
JButton btn7 = new JButton("0");
btn7.addActionListener(al);
btn7.setBackground(new Color(224,224,224));
btn7.setPreferredSize(new Dimension(70, 60));
btn7.setBorder (BorderFactory.createRaisedSoftBevelBorder()) ;
btn7.setFont(new Font("Sans Serif", Font.BOLD,20));
JButton btn8 = new JButton(".");
btn8.addActionListener(al);
btn8.setBackground(new Color(224,224,224));
btn8.setPreferredSize(new Dimension(70, 60));
btn8.setBorder (BorderFactory.createRaisedSoftBevelBorder()) ;
btn8.setFont(new Font("Sans Serif", Font.BOLD,20));
JButton btn9 = new JButton("=");
btn9.addActionListener(ol);
btn9.setBackground(new Color(0,128,255));
btn9.setBorder (BorderFactory.createEtchedBorder()) ;
btn9.setPreferredSize(new Dimension(70, 60));
btn9.setFont(new Font("Sans Serif", Font.BOLD,20));
btn9.setToolTipText("calculate result");
JButton btn1 = new JButton("CE");
btn1.addActionListener(ol);
btn1.setBackground(new Color(160,160,160));
btn1.setPreferredSize(new Dimension(50, 40));
btn1.setFont(new Font("Sans Serif", Font.BOLD,12));
btn1.setToolTipText("clear entry");
JButton btn2 = new JButton("C");
btn2.addActionListener(ol);
btn2.setBackground(new Color(160,160,160));
btn2.setPreferredSize(new Dimension(50, 40));
btn2.setFont(new Font("Sans Serif", Font.BOLD,15));
btn2.setToolTipText("clear");
JButton btn3 = new JButton("/");
btn3.addActionListener(ol);
btn3.setBackground(new Color(160,160,160));
btn3.setPreferredSize(new Dimension(50, 40));
btn3.setFont(new Font("Sans Serif", Font.BOLD,15));
btn3.setToolTipText("divide");
JButton btn4 = new JButton("*");
btn4.addActionListener(ol);
btn4.setBackground(new Color(160,160,160));
btn4.setPreferredSize(new Dimension(50, 40));
btn4.setFont(new Font("Sans Serif", Font.BOLD,15));
btn4.setToolTipText("multiplie");
JButton btn5 = new JButton("-");
btn5.addActionListener(ol);
btn5.setBackground(new Color(160,160,160));
btn5.setPreferredSize(new Dimension(50, 40));
btn5.setFont(new Font("Sans Serif", Font.BOLD,15));
btn5.setToolTipText("subtract");
JButton btn6 = new JButton("+");
btn6.addActionListener(ol);
btn6.setBackground(new Color(160,160,160));
btn6.setPreferredSize(new Dimension(50, 40));
btn6.setFont(new Font("Sans Serif", Font.BOLD,15));
btn6.setToolTipText("add");
this.add(txtArea, BorderLayout.NORTH);
this.add(panel,BorderLayout.CENTER);
this.add(panel2,BorderLayout.EAST);
panel.add(btn7);
panel.add(btn8);
panel.add(btn9);
panel2.add(btn1);
panel2.add(btn2);
panel2.add(btn3);
panel2.add(btn4);
panel2.add(btn5);
panel2.add(btn6);
this.setJMenuBar(menuBar);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.pack();
this.setResizable(false);
this.setVisible(true);
}
}
public class MyActionListener implements ActionListener {
JTextArea area;
public MyActionListener(JTextArea area){
this.area = area;
}
@Override
public void actionPerformed(ActionEvent e) {
JButton x = (JButton) e.getSource();
String y = x.getText();
String z = area.getText();
int v = area.getText().length();
int i = z.indexOf('.');
if(i==1 && "0".equals(area.getText())){
area.setText("");
}
if(v<15){
if(i>=0&&".".equals(y)){
area.append("");
}else{
area.append(y);
}
}else{
Toolkit.getDefaultToolkit().beep();
}
}
}
public class MyOperatorListener implements ActionListener {
JTextArea area;
double total;
public MyOperatorListener(JTextArea area){
this.area = area;
}
@Override
public void actionPerformed(ActionEvent e) {
JButton x = (JButton) e.getSource();
String y = x.getText();
double calc = Double.parseDouble(area.getText());
switch(y){
case "+": total = total + calc;
break;
case "-": total = total - calc;
break;
case "*": total = total * calc;
break;
case "/": if(calc!=0){
total = total / calc;
}
break;
default: break;
}
switch(y){
case "CE": calc = 0;
area.setText("0");
break;
case "C": total = 0;
calc = 0;
area.setText("0");
break;
case "=": area.setText(Double.toString(total));
break;
}
}
}
答案 0 :(得分：1)
在您的操作侦听器中，仅在按下C时初始化总计。使用3 + 5的这个例子：
total = total + calc; area.append(y); 输入数字后，总数不会更新。
理想情况下，您希望输入和存储第一个数字（总计），然后在按下所需操作时，清除该区域以允许输入第二个数字。然后，equals操作通过调用要使用的操作来评估整个表达式。
total + 5，因为它记得正在使用+操作。