我发布了一个关于如何实现actionlisteners的上一个问题。 香港专业教育学院完成了这个课程，我认为可能在阵列方面做得更好。 但这种方式对我有用。 问题是。当我点击清除按钮时它不会清除它，因为我的数字按钮上有更新变量，当按下它时存储数字。如果这是有道理的。
有没有办法可以解决它？
<!DOCTYPE html>
<html>
<head>
<title>Digital Goods</title>
</head>
<body>
<form id="myContainer" method="post" action="paypal/checkout.php">
<img src="https://www.vanishingincmagic.co.uk/gallery/photos/the-modern-con-man.jpg">
<p>$4.99</p>
<p>Buy my totally not fake book!</p>
</form>
<script>window.paypalCheckoutReady=function(){paypal.checkout.setup('EMAIL-HERE',{environment:'sandbox',container:'myContainer'})};</script>
<script src="//www.paypalobjects.com/api/checkout.js" async></script>
</body>
</html>
// import packages
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
// class
public class Lab31Panel extends JPanel {
// data declarations
private JRadioButton k2pButton;
private JRadioButton p2kButton;
private ButtonGroup weight;
private JPanel selectConversion;
private JButton jb0, jb1, jb2, jb3, jb4, jb5, jb6, jb7, jb8, jb9, jbminus, jbclear, jbconvert;
private JTextArea display;
private String update = "";
//constructor to initiate data and set up GUI
public Lab31Panel() {
setLayout(new BorderLayout());
// organizing radio buttons and their behaviours
k2pButton = new JRadioButton("Kilograms to Pounds");
p2kButton = new JRadioButton("Pounds to Kilograms");
weight = new ButtonGroup();
weight.add(k2pButton);
weight.add(p2kButton);
// adding components to panel to be south of the GUI
selectConversion = new JPanel();
selectConversion.add(k2pButton);
selectConversion.add(p2kButton);
add(selectConversion, BorderLayout.SOUTH);
//setting up west area of GUI
JPanel westPanel = new JPanel();
JPanel convert = new JPanel();
// setting up components for the west of the GUI
westPanel.setLayout(new GridLayout(5, 3));
westPanel.add(jb0 = new JButton("0"));
westPanel.add(jb1 = new JButton("1"));
westPanel.add(jb2 = new JButton("2"));
westPanel.add(jb3 = new JButton("3"));
westPanel.add(jb4 = new JButton("4"));
westPanel.add(jb5 = new JButton("5"));
westPanel.add(jb6 = new JButton("6"));
westPanel.add(jb7 = new JButton("7"));
westPanel.add(jb8 = new JButton("8"));
westPanel.add(jb9 = new JButton("9"));
westPanel.add(jbminus = new JButton("-"));
westPanel.add(jbclear = new JButton("clear"));
westPanel.add(jbconvert = new JButton("convert"));
add(westPanel, BorderLayout.WEST);
//setting up east components
JPanel eastPanel = new JPanel();
eastPanel.setLayout(new BorderLayout());
display = new JTextArea();
display.setEditable(false);
eastPanel.add(display, BorderLayout.CENTER);
add(eastPanel);
jb0.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Object source = e.getSource();
if (source == jb0) update += 0;
display.setText(update);
}
});
jb1.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Object source = e.getSource();
if (source == jb1) update += 1;
display.setText(update);
}
});
jb2.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Object source = e.getSource();
if (source == jb2) update += 2;
display.setText(update);
}
});
jb3.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Object source = e.getSource();
if (source == jb3) update += 3;
display.setText(update);
}
});
jb4.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Object source = e.getSource();
if (source == jb4) update += 4;
display.setText(update);
}
});
jb5.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Object source = e.getSource();
if (source == jb5) update += 5;
display.setText(update);
}
});
jb6.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Object source = e.getSource();
if (source == jb6) update += 6;
display.setText(update);
}
});
jb7.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Object source = e.getSource();
if (source == jb7) update += 7;
display.setText(update);
}
});
jb8.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Object source = e.getSource();
if (source == jb8) update += 8;
display.setText(update);
}
});
jb9.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Object source = e.getSource();
if (source == jb9) update += 9;
display.setText(update);
}
});
jbclear.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Object source = e.getSource();
if (source == jbclear) display.setText(null);
}
});
jbconvert.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Object source = e.getSource();
double convert = Double.parseDouble(update);
double totalp2k = convert / 2.24;
double totalk2p = convert * 2.24;
if (p2kButton.isSelected() == true) {
if (source == jbconvert) {
display.setText(update + " : " + totalp2k);
}
} else if (k2pButton.isSelected() == true) {
display.setText(update + " : " + totalk2p);
}
}
});
} //end constructor
} // end class
答案 0 :(得分：1)
在jbclear的ActionListener中，您还需要清除update：
jbclear.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
Object source = e.getSource();
if (source == jbclear) {
display.setText(null);
update = "";
}
}
});