我目前正在尝试一项包括JTree的学校任务。我想研究一些方法来添加，删除或移动JTree中的某些节点（通过鼠标单击选择节点），但是每当我单击JTree中的某个项目时，我都会得到“ AWT-EventQueue-0” -EventQueue-0”。我一直在努力想办法，但我一无所知。关于我做错了什么，我能否得到一点提示？谢谢。
package poo_tp9_dev;
import java.awt.List;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import javax.swing.JOptionPane;
import javax.swing.JTree;
import javax.swing.event.TreeSelectionEvent;
import javax.swing.event.TreeSelectionListener;
import javax.swing.tree.DefaultMutableTreeNode;
import javax.swing.tree.DefaultTreeModel;
import javax.swing.tree.MutableTreeNode;
public class MyJTree extends javax.swing.JFrame {
/**
* Creates new form MyJTree
*/
DefaultMutableTreeNode selectedNode = new DefaultMutableTreeNode();
public MyJTree() {
initComponents();
defaultTree();
}
public void defaultTree(){
DefaultTreeModel model = (DefaultTreeModel) myTree.getModel();
DefaultMutableTreeNode myroot = new DefaultMutableTreeNode("Product");
model.setRoot(myroot);
DefaultMutableTreeNode root = (DefaultMutableTreeNode) model.getRoot();
myTree = new JTree(root);
DefaultMutableTreeNode[] nodes = {new DefaultMutableTreeNode("Hardware Product"),new DefaultMutableTreeNode("Software Product")};
DefaultMutableTreeNode[] nodesr1 = {new DefaultMutableTreeNode("Video Card"),new DefaultMutableTreeNode("Monitor")};
DefaultMutableTreeNode[] nodesr2 = {new DefaultMutableTreeNode("Game"),new DefaultMutableTreeNode("Programming Language")};
root.add(nodes[0]);
root.add(nodes[1]);
ArrayList<DefaultMutableTreeNode> list = Collections.list(root.children());
DefaultMutableTreeNode selectedNode = (DefaultMutableTreeNode) myTree.getLastSelectedPathComponent();
list.get(0).add(nodesr1[0]);
list.get(0).add(nodesr1[1]);
list.get(1).add(nodesr2[0]);
list.get(1).add(nodesr2[1]);
}
/**
* This method is called from within the constructor to initialize the form.
* WARNING: Do NOT modify this code. The content of this method is always
* regenerated by the Form Editor.
*/
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {
jScrollPane1 = new javax.swing.JScrollPane();
myTree = new javax.swing.JTree();
btnAdd = new javax.swing.JButton();
btnMove = new javax.swing.JButton();
btnDelete = new javax.swing.JButton();
setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
javax.swing.tree.DefaultMutableTreeNode treeNode1 = new javax.swing.tree.DefaultMutableTreeNode("root");
myTree.setModel(new javax.swing.tree.DefaultTreeModel(treeNode1));
myTree.addMouseListener(new java.awt.event.MouseAdapter() {
public void mouseClicked(java.awt.event.MouseEvent evt) {
myTreeMouseClicked(evt);
}
});
jScrollPane1.setViewportView(myTree);
btnAdd.setText("Add");
btnAdd.addMouseListener(new java.awt.event.MouseAdapter() {
public void mouseClicked(java.awt.event.MouseEvent evt) {
btnAddMouseClicked(evt);
}
});
btnMove.setText("Move");
btnDelete.setText("Delete");
javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
getContentPane().setLayout(layout);
layout.setHorizontalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 226, javax.swing.GroupLayout.PREFERRED_SIZE)
.addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 46, Short.MAX_VALUE)
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addComponent(btnMove, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.PREFERRED_SIZE, 80, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(btnAdd, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.PREFERRED_SIZE, 80, javax.swing.GroupLayout.PREFERRED_SIZE)
.addComponent(btnDelete, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.PREFERRED_SIZE, 80, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGap(38, 38, 38))
);
layout.setVerticalGroup(
layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
.addGroup(layout.createSequentialGroup()
.addContainerGap()
.addComponent(jScrollPane1, javax.swing.GroupLayout.PREFERRED_SIZE, 275, javax.swing.GroupLayout.PREFERRED_SIZE))
.addGroup(layout.createSequentialGroup()
.addGap(48, 48, 48)
.addComponent(btnAdd)
.addGap(18, 18, 18)
.addComponent(btnMove)
.addGap(18, 18, 18)
.addComponent(btnDelete)))
.addContainerGap(14, Short.MAX_VALUE))
);
pack();
}// </editor-fold>
private void btnAddMouseClicked(java.awt.event.MouseEvent evt) {
// TODO add your handling code here:
DefaultTreeModel model = (DefaultTreeModel) myTree.getModel();
String userinput = JOptionPane.showInputDialog("Input node name:");
DefaultMutableTreeNode n = new DefaultMutableTreeNode(userinput);
selectedNode.add(n);
model.reload();
}
private void myTreeMouseClicked(java.awt.event.MouseEvent evt) {
this.selectedNode=(DefaultMutableTreeNode)
myTree.getLastSelectedPathComponent();
}
/**
* @param args the command line arguments
*/
public static void main(String args[]) {
/* Set the Nimbus look and feel */
//<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
/* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
* For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html
*/
try {
for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
if ("Nimbus".equals(info.getName())) {
javax.swing.UIManager.setLookAndFeel(info.getClassName());
break;
}
}
} catch (ClassNotFoundException ex) {
java.util.logging.Logger.getLogger(MyJTree.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (InstantiationException ex) {
java.util.logging.Logger.getLogger(MyJTree.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (IllegalAccessException ex) {
java.util.logging.Logger.getLogger(MyJTree.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
} catch (javax.swing.UnsupportedLookAndFeelException ex) {
java.util.logging.Logger.getLogger(MyJTree.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
}
//</editor-fold>
/* Create and display the form */
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new MyJTree().setVisible(true);
}
});
}
// Variables declaration - do not modify
private javax.swing.JButton btnAdd;
private javax.swing.JButton btnDelete;
private javax.swing.JButton btnMove;
private javax.swing.JScrollPane jScrollPane1;
private javax.swing.JTree myTree;
// End of variables declaration
}
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at poo_tp9_dev.MyJTree.btnAddMouseClicked(MyJTree.java:176)
at poo_tp9_dev.MyJTree.access$100(MyJTree.java:24)
at poo_tp9_dev.MyJTree$2.mouseClicked(MyJTree.java:122)
at java.awt.AWTEventMulticaster.mouseClicked(AWTEventMulticaster.java:270)
at java.awt.Component.processMouseEvent(Component.java:6542)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
at java.awt.Component.processEvent(Component.java:6304)
at java.awt.Container.processEvent(Container.java:2239)
at java.awt.Component.dispatchEventImpl(Component.java:4889)
at java.awt.Container.dispatchEventImpl(Container.java:2297)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4904)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4544)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4476)
at java.awt.Container.dispatchEventImpl(Container.java:2283)
at java.awt.Window.dispatchEventImpl(Window.java:2746)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:760)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:84)
at java.awt.EventQueue$4.run(EventQueue.java:733)
at java.awt.EventQueue$4.run(EventQueue.java:731)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:730)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205)
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)