基本上我遇到了错误:
run:Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at PaintV2.UIPanel$1.actionPerformed(PaintGUI.java:line marked)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2346)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6527)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6292)
at java.awt.Container.processEvent(Container.java:2234)
at java.awt.Component.dispatchEventImpl(Component.java:4883)
at java.awt.Container.dispatchEventImpl(Container.java:2292)
at java.awt.Component.dispatchEvent(Component.java:4705)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4898)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4533)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4462)
at java.awt.Container.dispatchEventImpl(Container.java:2278)
at java.awt.Window.dispatchEventImpl(Window.java:2739)
at java.awt.Component.dispatchEvent(Component.java:4705)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:746)
at java.awt.EventQueue.access$400(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:697)
at java.awt.EventQueue$3.run(EventQueue.java:691)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:719)
at java.awt.EventQueue$4.run(EventQueue.java:717)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:75)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:716)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)'
当我制作绘画应用程序时，我试图将我的 GUI 链接到颜色类。我的问题是:我的代码出了什么问题？如果有人知道如何修复它，请您解释一下如何修复它
我的主要方法:
package PaintV2;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.HashMap;
public class PaintGUI{
public static void main(String[] args ){
JFrame frame = new JFrame("test panel 2");
MainPanel panel = new MainPanel();
UIPanel uip = new UIPanel(panel);
frame.setLayout(new BorderLayout());
frame.add(uip, BorderLayout.NORTH);
frame.add(panel, BorderLayout.CENTER);
frame.setSize(900, 900);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
我的 MainPanel 类:
class MainPanel extends JPanel {
int px, py; // radius
public Color colvals;
public Colour col;
public MainPanel(){
this.addMouseMotionListener(new MouseMotionAdapter() {
// store drag coordinates and repaint
public void mouseDragged( MouseEvent event )
{
px = event.getX();
py = event.getY();
repaint();
}
}); // end call to addMouseMotionListener
}
public void paint( Graphics g )
{
g.setColor(Color.RED);
g.fillOval( px, py, 15, 15 );
}
}
我的 UIPanel 类:
class UIPanel extends JPanel {
public MainPanel gpanel;
public Integer data;
public Color colval;
public Colour col;
public UIPanel(MainPanel panel) {
gpanel = panel;
Box btnBox = Box.createHorizontalBox();
btnBox.add(Box.createHorizontalGlue());
JButton setBtn = new JButton("Set");
//code for the colour chooser
//decided to use a dropdow list with hashmap
final DefaultComboBoxModel colour = new DefaultComboBoxModel();
colour.addElement("Red");
colour.addElement("Blue");
colour.addElement("Yellow");
colour.addElement("Green");
final JComboBox colours = new JComboBox(colour);
JScrollPane colourScroll = new JScrollPane(colours);
JButton freeBtn = new JButton("FreeHand");
JButton rectBtn = new JButton("Rectangle");
JButton circBtn = new JButton("Circle");
JButton lineBtn = new JButton("line");
btnBox.add(setBtn);
btnBox.add(colourScroll);
btnBox.add(freeBtn);
btnBox.add(rectBtn);
btnBox.add(circBtn);
btnBox.add(lineBtn);
btnBox.setSize(300, 100);
btnBox.add(Box.createHorizontalGlue());
add(btnBox, BorderLayout.NORTH);
setBtn.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e) {
data= colours.getSelectedIndex();
col.setCol(data);//This is where the error is being flagged up
}
});
}
}
和颜色类别
package PaintV2;
import java.awt.*;
import java.awt.event.*;
import java.util.HashMap;
import javax.swing.*;
public class Colour{
public Color colVal;
HashMap<Integer, Color> map = new HashMap<Integer, Color>();
public Colour() {
map.put(0, Color.RED);
map.put(1, Color.BLUE);
map.put(2, Color.YELLOW);
map.put(3, Color.GREEN);
}
public Color setCol(Integer data) {
return map.get(data);
}
}
提前对大量代码和代码困惑表示歉意。另外，如果您需要我编辑任何内容以使其更容易理解，请发布或发布其他内容，我会在可能的情况下对其进行编辑。
最佳答案
似乎您刚刚声明了 col 且未初始化。尝试这样..
public void actionPerformed(ActionEvent e) {
data= colours.getSelectedIndex();
if(col == null)
col = new Colour();
col.setCol(data);//This is where the error is being flagged up
}
关于java - 连接到另一个类时 AWT-EventQueue-0 java.lang.NullPointerException，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/27018791/