Why "parent is null"?
Hi guys,
I'm developing a simple Applet application with JDK 1.3.1.
All of codes are the following,
DemoApplet.java
public class DemoApplet extends Applet {
private static final long serialVersionUID = -371112038768840393;
public DemoApplet() {
BorderLayout gridLayout = new BorderLayout();
setLayout(gridLayout);
add(new DemoPanel(), BorderLayout.CENTER);
public void init() {
}DemoPanel.java
public class DemoPanel extends Panel {
private static final long serialVersionUID = -5992125460349250223;
private DemoPopupMenu popupMenu = new DemoPopupMenu();
public DemoPanel() {
addMouseListener(mouseAdapter);
private MouseAdapter mouseAdapter = new MouseAdapter() {
public void mouseClicked(MouseEvent e) {
if (SwingUtilities.isRightMouseButton(e)) {
popupMenu
.show((DemoPanel) e.getComponent(), e.getX(), e.getY());
}DemoPopupMenu .java
public class DemoPopupMenu extends PopupMenu {
private static final long serialVersionUID = -7751149413579159572;
private Menu menu = new Menu("PopuMenu");
public DemoPopupMenu() {
add(menu);
}When I run DemoApplet with appletviewer, an exception was thrown:
Exception occurred during event dispatching:
java.lang.NullPointerException: parent is null
at java.awt.PopupMenu.show(PopupMenu.java:102)
at test.demo.DemoPanel$1.mouseClicked(DemoPanel.java:23)
at java.awt.Component.processMouseEvent(Component.java:3713)
at java.awt.Component.processEvent(Component.java:3539)
at java.awt.Container.processEvent(Container.java:1159)
at java.awt.Component.dispatchEventImpl(Component.java:2588)
at java.awt.Container.dispatchEventImpl(Container.java:1208)
at java.awt.Component.dispatchEvent(Component.java:2492)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:334)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:126)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:88)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:80) But if I changed all of PopupMenu/Menu to JPopupMenu/JMenu, all was OK.
Although the old AWT codes aren't recommended, I don't think the application is wrong.
I'm puzzled by the matter.
I wish some friend would explain the matter.
Thanks in advance!
a cup of Java, cheers!
Sha Jiang
Edited by: jiangshachina on Oct 29, 2007 4:44 PM
Oh, I get it.
Thanks for the reply.
Rewards a Duck star :-D
You never added the popupMenu to anything. Therefore, it has no parent and is not part of any component hierarchy.With the error output, I known the DemoPopupMenu need a "parent" component.
But I simple think DemoPanel is the parent for DemoPopupMenu,
because DemoPopupMenu is included by DemoPanel (so foolish!)
Also, you should not use isRightMouseButton() for handling popup actions.
There is a method called isPopupTrigger() in the MouseEvent class.
Call this in the mousePressed() and mouseReleased() methods of your MouseListener (instead of mouseClicked).I know the method isPopupTrigger().
In fact, at the beginning, I used isPopupTrigger(), but it didn't work.
Whether I right-click or left-click, both of the values of isPopupTrigger() are "false".
Then I have to redirect to isRightMouseButton() :-(
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Edited by: 897674 on Jan 3, 2012 10:44 AM
Edited by: 897674 on Jan 3, 2012 10:46 AM -
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trees.insertNode((Edge)temp.elementAt(y));
return trees;
public void printTree(Tree tree)
System.out.print("("+tree.rootNode.edge.fromNode.getObjName()+","+tree.rootNode.edge.toNode.getObjName()+")");
Vector siblings = tree.rootNode.childrens;
for(int i = 0; i < siblings.size();i++)
TreeNode node = (TreeNode)siblings.elementAt(i);
System.out.print("("+node.edge.fromNode.getObjName()+","+node.edge.toNode.getObjName()+")");
System.out.println();
public Vector initializeTrees(Vector edges)
Vector trees = new Vector();
for(int i = 0;i < edges.size();i++)
Vector temp = (Vector)edges.elementAt(i);
for(int j = 0;j < temp.size();j++)
Tree tree = new Tree();
tree.insertNode((Edge)temp.elementAt(j));
trees.add(tree);
return trees;
public synchronized void insertNode(Edge edge)
if(rootNode == null)
rootNode = new TreeNode(edge);
else
rootNode.insert(edge);
EdgeGenerator class
package SPO;
import java.util.*;
import k_means.*;
public class EdgeGenerator
public EdgeGenerator()
public Vector createEdges(Vector dataPoints)
//OrderPair orderPair = new OrderPair();
Vector edges = new Vector();
for(int i = 0;i < dataPoints.size()-1 ;i++)
Vector temp = new Vector();
for(int j = i+1;j < dataPoints.size();j++)
//Create an order of edges
Edge edge = new Edge((DataPoint)dataPoints.elementAt(i),(DataPoint)dataPoints.elementAt(j));
temp.add(edge);
edges.add(temp);
return edges;
Edge class
package SPO;
import k_means.*;
public class Edge
public DataPoint toNode;
public DataPoint fromNode;
public Edge(DataPoint x,DataPoint y)
if (x.getX() > y.getX())
this.fromNode = x;
this.toNode = y;
else
this.fromNode=y;
this.toNode = x;
Entry Point
package SPO;
import java.util.*;
import k_means.*;
public class Tester {
public static void main(String[] args)
Vector dataPoints = new Vector();
dataPoints.add(new DataPoint(140, "Orange"));
dataPoints.add(new DataPoint(114.2, "Lemmon"));
dataPoints.add(new DataPoint(111.5, "Coke"));
dataPoints.add(new DataPoint(104.6, "Pine apple"));
dataPoints.add(new DataPoint(94.1, "W grape"));
dataPoints.add(new DataPoint(85.2, "Appletizer"));
dataPoints.add(new DataPoint(84.8, "R Grape"));
dataPoints.add(new DataPoint(74.2, "Sprite"));
dataPoints.add(new DataPoint(69.2, "Granadilla"));
dataPoints.add(new DataPoint(59, "Strawbery"));
dataPoints.add(new DataPoint(45.5, "Stone"));
dataPoints.add(new DataPoint(36.3, "Yam"));
dataPoints.add(new DataPoint(27, "Cocoa"));
dataPoints.add(new DataPoint(13.8, "Pawpaw"));
EdgeGenerator eg = new EdgeGenerator();
Vector edges = eg.createEdges(dataPoints);
Tree treeMaker = new Tree();
Vector partialTrees = treeMaker.initializeTrees(edges);
Tree [] trees = treeMaker.createTrees(partialTrees,edges);
for(int i = 0;i < trees.length;i++)
treeMaker.printTree(trees[i]);
The program output
Each and every "@" symbol represents the start of a tree
@(Orange,Lemmon)(Lemmon,Coke)(Lemmon,Coke)(Lemmon,Coke)(Lemmon,Coke)(Lemmon,Coke)(Lemmon,Coke)(Lemmon,Coke)(Lemmon,Coke)(Lemmon,Coke)(Lemmon,Coke)(Lemmon,Coke)(Lemmon,Coke)
@(Orange,Coke)(Coke,Pine apple)(Coke,Pine apple)(Coke,Pine apple)(Coke,Pine apple)(Coke,Pine apple)(Coke,Pine apple)(Coke,Pine apple)(Coke,Pine apple)(Coke,Pine apple)(Coke,Pine apple)(Coke,Pine apple)
@(Orange,Pine apple)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)
@(Orange,W grape)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)
@(Orange,Appletizer)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)
@(Orange,R Grape)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)
@(Orange,Sprite)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)
@(Orange,Granadilla)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)
@(Orange,Strawbery)(Strawbery,Stone)(Strawbery,Stone)(Strawbery,Stone)(Strawbery,Stone)
@(Orange,Stone)(Stone,Yam)(Stone,Yam)(Stone,Yam)
@(Orange,Yam)(Yam,Cocoa)(Yam,Cocoa)
@(Orange,Cocoa)(Cocoa,Pawpaw)
@(Orange,Pawpaw)
@(Lemmon,Coke)(Coke,Pine apple)(Coke,Pine apple)(Coke,Pine apple)(Coke,Pine apple)(Coke,Pine apple)(Coke,Pine apple)(Coke,Pine apple)(Coke,Pine apple)(Coke,Pine apple)(Coke,Pine apple)(Coke,Pine apple)
@(Lemmon,Pine apple)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)
@(Lemmon,W grape)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)
@(Lemmon,Appletizer)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)
@(Lemmon,R Grape)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)
@(Lemmon,Sprite)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)
@(Lemmon,Granadilla)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)
@(Lemmon,Strawbery)(Strawbery,Stone)(Strawbery,Stone)(Strawbery,Stone)(Strawbery,Stone)
@(Lemmon,Stone)(Stone,Yam)(Stone,Yam)(Stone,Yam)
@(Lemmon,Yam)(Yam,Cocoa)(Yam,Cocoa)
@(Lemmon,Cocoa)(Cocoa,Pawpaw)
@(Lemmon,Pawpaw)
@(Coke,Pine apple)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)(Pine apple,W grape)
@(Coke,W grape)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)
@(Coke,Appletizer)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)
@(Coke,R Grape)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)
@(Coke,Sprite)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)
@(Coke,Granadilla)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)
@(Coke,Strawbery)(Strawbery,Stone)(Strawbery,Stone)(Strawbery,Stone)(Strawbery,Stone)
@(Coke,Stone)(Stone,Yam)(Stone,Yam)(Stone,Yam)
@(Coke,Yam)(Yam,Cocoa)(Yam,Cocoa)
@(Coke,Cocoa)(Cocoa,Pawpaw)
@(Coke,Pawpaw)
@(Pine apple,W grape)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)(W grape,Appletizer)
@(Pine apple,Appletizer)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)
@(Pine apple,R Grape)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)
@(Pine apple,Sprite)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)
@(Pine apple,Granadilla)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)
@(Pine apple,Strawbery)(Strawbery,Stone)(Strawbery,Stone)(Strawbery,Stone)(Strawbery,Stone)
@(Pine apple,Stone)(Stone,Yam)(Stone,Yam)(Stone,Yam)
@(Pine apple,Yam)(Yam,Cocoa)(Yam,Cocoa)
@(Pine apple,Cocoa)(Cocoa,Pawpaw)
@(Pine apple,Pawpaw)
@(W grape,Appletizer)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)(Appletizer,R Grape)
@(W grape,R Grape)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)
@(W grape,Sprite)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)
@(W grape,Granadilla)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)
@(W grape,Strawbery)(Strawbery,Stone)(Strawbery,Stone)(Strawbery,Stone)(Strawbery,Stone)
@(W grape,Stone)(Stone,Yam)(Stone,Yam)(Stone,Yam)
@(W grape,Yam)(Yam,Cocoa)(Yam,Cocoa)
@(W grape,Cocoa)(Cocoa,Pawpaw)
@(W grape,Pawpaw)
@(Appletizer,R Grape)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)(R Grape,Sprite)
@(Appletizer,Sprite)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)
@(Appletizer,Granadilla)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)
@(Appletizer,Strawbery)(Strawbery,Stone)(Strawbery,Stone)(Strawbery,Stone)(Strawbery,Stone)
@(Appletizer,Stone)(Stone,Yam)(Stone,Yam)(Stone,Yam)
@(Appletizer,Yam)(Yam,Cocoa)(Yam,Cocoa)
@(Appletizer,Cocoa)(Cocoa,Pawpaw)
@(Appletizer,Pawpaw)
@(R Grape,Sprite)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)(Sprite,Granadilla)
@(R Grape,Granadilla)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)
@(R Grape,Strawbery)(Strawbery,Stone)(Strawbery,Stone)(Strawbery,Stone)(Strawbery,Stone)
@(R Grape,Stone)(Stone,Yam)(Stone,Yam)(Stone,Yam)
@(R Grape,Yam)(Yam,Cocoa)(Yam,Cocoa)
@(R Grape,Cocoa)(Cocoa,Pawpaw)
@(R Grape,Pawpaw)
@(Sprite,Granadilla)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)(Granadilla,Strawbery)
@(Sprite,Strawbery)(Strawbery,Stone)(Strawbery,Stone)(Strawbery,Stone)(Strawbery,Stone)
@(Sprite,Stone)(Stone,Yam)(Stone,Yam)(Stone,Yam)
@(Sprite,Yam)(Yam,Cocoa)(Yam,Cocoa)
@(Sprite,Cocoa)(Cocoa,Pawpaw)
@(Sprite,Pawpaw)
@(Granadilla,Strawbery)(Strawbery,Stone)(Strawbery,Stone)(Strawbery,Stone)(Strawbery,Stone)
@(Granadilla,Stone)(Stone,Yam)(Stone,Yam)(Stone,Yam)
@(Granadilla,Yam)(Yam,Cocoa)(Yam,Cocoa)
@(Granadilla,Cocoa)(Cocoa,Pawpaw)
@(Granadilla,Pawpaw)
@(Strawbery,Stone)(Stone,Yam)(Stone,Yam)(Stone,Yam)
@(Strawbery,Yam)(Yam,Cocoa)(Yam,Cocoa)
@(Strawbery,Cocoa)(Cocoa,Pawpaw)
@(Strawbery,Pawpaw)
@(Stone,Yam)(Yam,Cocoa)(Yam,Cocoa)
@(Stone,Cocoa)(Cocoa,Pawpaw)
@(Stone,Pawpaw)
@(Yam,Cocoa)(Cocoa,Pawpaw)
@(Yam,Pawpaw)
@(Cocoa,Pawpaw)Your program description makes no sense. What exactly is it supposed to do?
Your errors make no sense. What is it doing wrong?
Your program output makes no sense. Look up pre-order, in-order, and post-order notation for representing trees. Pick one of those that you think would be best. I would go with pre-order. Because what you are doing isn't understandable.
By the way, I think your concept of a tree is flawed. A node in a tree has 3 things. it has a reference to its parent, it has references to any of its children, and it has some key value that represents the node (if each node were represented by numbers, the value would be an integer or something). In the case of the root, its reference to its parent is null. I don't know what you are doing with your tree, but it is highly confusing. -
Hello to all the Apex champs out there, can you please help me with the following problem:
I have a table, and in its simplified version, it has the following rows:
Id Pid Description
1 NULL Id 1, Parent Id NULL
2 1 Id 2, Parent Id 1
3 2 Id 3, Parent Id 2
4 1 Id 4, Parent Id 1
5 4 Id 5, Parent Id 4
When these rows are displayed in a tree, the output is:
Id 1, Parent Id NULL
Id 2, Parent Id 1
Id 3, Parent Id 2
Id 4, Parent Id 1
Id 5, Parent Id 4
I am on a form page that already shows the record with id as 1 (and the tree root id as 1), and I need to display only the children for 1, i.e.
Id 2, Parent Id 1
Id 3, Parent Id 2
Id 4, Parent Id 1
Id 5, Parent Id 4
Is there a way by which I can suppress the first Parent Id record as I am already viewing the record on the page?
Many thanks in advance.
Regards,
DhruvaHi,
Your tree must contain a root node - that is, the top parent in the tree.
You can, however, hide this by replacing the contents of the tree's Parent Node Template with &nbsp; (you have to put something in the setting otherwise Apex will reset it to the default contents).
Andy
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