JButton setText()错误
JButton setText()错误
提问于 2014-11-12 16:03:33
当你按下按钮时，我正试着把一个新文本设置成一个按钮。但是它似乎不起作用，我做错了什么，我不知道.
编辑
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class GrowAndShrinkSquareGUItest {
JFrame frame;
SquareDrawPanel bigGreen;
SquareDrawPanel smallGreen;
JButton button;
growAndShrinkListener listener;
public class SquareDrawPanel extends JPanel {
int width;
int height;
SquareDrawPanel(int w, int h) {
width = w;
height = h;
}
public void paintComponent(Graphics g) {
g.setColor(Color.green);
g.fillRect(frame.getWidth() / 2 - (width / 2), frame.getHeight()
/ 2 - (height / 2) - 15, width, height);
}
}
public class growAndShrinkListener implements ActionListener {
// JButton button;
growAndShrinkListener(JButton button) {
button = new JButton("Click me to grow the Square");
frame.add(button, BorderLayout.NORTH);
button.addActionListener(this);
}
@Override
public void actionPerformed(ActionEvent e) {
button.setText("Unselect all");
}
}
public static void main(String[] args) {
GrowAndShrinkSquareGUItest test = new GrowAndShrinkSquareGUItest();
test.go();
}
private void createPanels() {
bigGreen = new SquareDrawPanel(400, 400);
smallGreen = new SquareDrawPanel(100, 100);
}
private void drawPanel(JPanel panel) {
frame.add(panel);
panel.setVisible(true);
frame.add(panel, BorderLayout.CENTER);
}
private void createListenerButton() {
listener = new growAndShrinkListener(button);
}
private void loop(){}
public void go() {
frame = new JFrame();
frame.setSize(500, 500);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
createPanels();
drawPanel(smallGreen);
createListenerButton();
frame.setVisible(true);
}}
回答 3
Stack Overflow用户
回答已采纳
发布于 2014-11-12 16:16:58
这是因为您使用了在button方法的作用域中没有定义的actionPerformed变量。Java变量有作用域，它们在定义它们的大括号中可用。actionPerformed方法脱离了growAndShrinkListener方法的大括号。固定代码：
public class growAndShrinkListener implements ActionListener {
growAndShrinkListener(JButton button) {
button = new JButton("Click me to grow the Square");
frame.add(button, BorderLayout.NORTH);
button.addActionListener(this);
}
@Override
public void actionPerformed(ActionEvent e) {
Object source = e.getSource();
if(source instanceof JButton) {
button = (JButton) source;
button.setText("Click to shrink square");
}
}
}或者，您可以使用私有变量：
public class growAndShrinkListener implements ActionListener {
private JButton button;
growAndShrinkListener() {
button = new JButton("Click me to grow the Square");
frame.add(button, BorderLayout.NORTH);
button.addActionListener(this);
}
@Override
public void actionPerformed(ActionEvent e) {
button.setText("Click to shrink square");
}
}注意:您不应该在构造函数中覆盖参数的内容。您得到的参数不是一个指向被调用者变量的“指针”，而是对该变量的简单引用。如果您覆盖，那么内容将丢失您和calle将不知道这一点。
Stack Overflow用户
发布于 2014-11-12 16:17:45
像这样改变..。
public class YourSuperClass{
private JButton button;
public YourSuperClass(){
// your logics
button = new JButton();
button.addActionListener(new GrowAndShrinkListener(button));
frame.add(button, BorderLayout.NORTH);
}
class GrowAndShrinkListener implements ActionListener {
GrowAndShrinkListener(JButton button) {
}
@Override
public void actionPerformed(ActionEvent e) {
if(e.getSource() == button){
button.setText("Click to shrink square");
}
}
}
}Stack Overflow用户
发布于 2014-11-12 16:27:36
试试这个：
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
class frame extends JFrame
{
JButton b;
public frame()
{
setLayout(new BorderLayout());
b=new JButton("Press");
add(b,BorderLayout.SOUTH);
b.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e)
{
b.setText("Clicked");
}
});
}
public static void main (String[] args) {
frame f=new frame();
f.setExtendedState(MAXIMIZED_BOTH);
f.setVisible(true);
}
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/26891333
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