More on inner classes
Create a private inner class that implements a public
interface. Write a method that returns a reference to an instance of the private
inner class, upcast to the interface. Show that the inner class is completely
hidden by trying to downcast to it.
I didnot understand the last part of the question..Can anyone help me out?
That's actually pretty clear.
You have a public interface and a public outer class.
The outer class has an inner class marked as private which implements the interface. It also has a method that is defined as returning something that implements the interface, which you will satisfy by returning an instance of the inner class.
You have to show that the object you get back from the outer class's method cannot be cast to the inner class.
Similar Messages
-
Help: Factory Class using Inner Class and Private Constructor?
The situation is as follows:
I want a GamesCollection class that instantiates Game objects by looking up the information needed from a database. I would like to use Game outside of GamesCollection, but only have it instantiated by GamesCollection to ensure the game actually exist. Each Game object is linked to a database record. If a Game object exist, it must also exist in the database. Game objects can never be removed from the database.
I thought about making the Game object an inner class of GamesCollection, but this means that Game class constructor is still visible outside. So what if I made Game constructor private? Well, now I can't create Game objects without a static method inside Game class (static Object factory).
Basically what I need is a constructor for the inner Game class accessible to GamesCollection, but not to the rest of the world (including packages). Is there a way to do this?leesiulung wrote:
As a second look, I was initially confused about your first implementation, but it now makes more sense.
Let me make sure I understand this:
- the interface is needed to make the class accessible outside the outer classBetter: it is necessary to have a type that is accessible outside of GameCollection -- what else could be the return type of instance?
- the instance() method is the object factory
- the private modifier for the inner class is to prevent outside classes to instantiate this objectRight.
However, is a private inner class accessible in the outer class? Try it and see.
How does this affect private/public modifiers on inner classes?Take about five minutes and write a few tests. That should answer any questions you may have.
How do instantiate a GameImpl object? This basically goes back to the first question.Filling out the initial solution:
public interface Game {
String method();
public class GameCollection {
private static class GameImpl implements Game {
public String method() {
return "GameImpl";
public Game instance() {
return new GameImpl();
public static void main(String[] args) {
GameCollection app = new GameCollection();
Game game = app.instance();
System.out.println(game.method());
}Even if you were not interested in controlling game creation, defining interfaces for key concepts like Game is always going to be a good idea. Consider how you will write testing code, for example. How will you mock Game? -
How to pass a variable value to an inner class?
Hi there,
Please have a look of the code below. It's a bit long, but my concern is I did have to declare the int "i" variable as static because it is used by an inner class (if "i" is not declare as static, the code cannot be compiled).
Is there a more "clean" way to do the way work without declaring the "i" int as static? (because the scope of this variable is not the whole program).
Thanks for your help.
Denis
import java.util.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
class Tools{
static int i;
static void longTask(){
for (Tools.i=0; Tools.i<=100; Tools.i++) {
SwingUtilities.invokeLater( new Runnable(){
public void run(){
myApp.jpb.setValue(Tools.i);//--- static variable i
for (int j=0; j<200; j++)
System.out.println(Tools.i+" - "+j);
class myListener implements ActionListener{
public void actionPerformed(ActionEvent e){
Thread t = new Thread() {
public void run(){
Tools.longTask();
t.start();
public class myApp {
static JProgressBar jpb;
public static void main(String[] args) {
JFrame frame = new JFrame();
JPanel panel = new JPanel(new FlowLayout());
jpb = new JProgressBar();
jpb.setValue(0);
jpb.setStringPainted(true);
JButton button = new JButton("go");
button.addActionListener(new myListener());
panel.add(jpb);
panel.add(button);
frame.getContentPane().add( panel, BorderLayout.CENTER);
frame.setVisible(true);
frame.pack();
}Without compiling it, writing it in notepad, it would be something like this. You should also wonder if this longTask has to be static by the way. But I think this demonstrates the inner class stuff. You can also look in the tutorial on this site: http://java.sun.com/docs/books/tutorial/essential/threads/timer.html
class Tools{
static int i;
static void longTask(){
for (Tools.i=0; Tools.i<=100; Tools.i++) {
SwingUtilities.invokeLater( new Innerclass(i));
for (int j=0; j<200; j++) {
System.out.println(Tools.i+" - "+j);
Class Innerclass implements Runnable(){
int i;
public Innerclass(int i) {
this.i = i;
public void run(){
myApp.jpb.setValue(Tools.i);//--- static variable i
} -
Adding ItemListeners to an object created in an inner class?
Hi All,
I was wondering how dow you add ItemListeners to an object, thats created in an inner class of an outer class that implements the item listener interface. Or is it possible? I got around the problem by putting the createBox method in the outer class and calling it from the inner class, but it would be nice to know if you can keep it contained.
i.e (Assume everythings declared, libs are imported, interface is implemented in outer class etc.)
public class OuterClass implements ItemListener
// Stuff
class InnerClass
// Yet more stuff
void createBox (JPanel aPanel)
JCheckBox aBox = new JCheckBox;
aPanel.add(aBox)
// What should this line be ->
aBox.addItemListener(whatGoesHere?);
// More Stuff
}aBox.addItemListener(OuterClass.this);
-
Main method not found and how to put event handlers in an inner class
How would I put all the event handling methods in an inner class and I have another class that just that is just a main function, but when i try to run the project, it says main is not found. Here are the two classes, first one sets up everything and the second one is just main.
mport java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;
public class JournalFrame extends JFrame {
private JLabel dateLabel = new JLabel("Date: ");
private JTextField dateField = new JTextField(20);
private JPanel datePanel = new JPanel(new FlowLayout());
BorderLayout borderLayout1 = new BorderLayout();
JPanel radioPanel = new JPanel();
JPanel statusPanel = new JPanel();
JPanel textAreaPanel = new JPanel();
JPanel buttonPanel = new JPanel();
GridLayout gridLayout1 = new GridLayout();
FlowLayout flowLayout1 = new FlowLayout();
GridLayout gridLayout2 = new GridLayout();
GridLayout gridLayout3 = new GridLayout();
JRadioButton personalButton = new JRadioButton();
JRadioButton businessButton = new JRadioButton();
JLabel status = new JLabel();
JTextArea entryArea = new JTextArea();
JButton clearButton = new JButton();
JButton saveButton = new JButton();
ButtonGroup entryType = new ButtonGroup();
public JournalFrame(){
try {
jbInit();
catch(Exception e) {
e.printStackTrace();
private void initWidgets(){
private void jbInit() throws Exception {
this.getContentPane().setLayout(borderLayout1);
radioPanel.setLayout(gridLayout1);
statusPanel.setLayout(flowLayout1);
textAreaPanel.setLayout(gridLayout2);
buttonPanel.setLayout(gridLayout3);
personalButton.setSelected(true);
personalButton.setText("Personal");
personalButton.addActionListener(new JournalFrame_personalButton_actionAdapter(this));
businessButton.setText("Business");
status.setText("");
entryArea.setText("");
entryArea.setColumns(10);
entryArea.setLineWrap(true);
entryArea.setRows(30);
entryArea.setWrapStyleWord(true);
clearButton.setPreferredSize(new Dimension(125, 25));
clearButton.setText("Clear Journal Entry");
clearButton.addActionListener(new JournalFrame_clearButton_actionAdapter(this));
saveButton.setText("Save Journal Entry");
saveButton.addActionListener(new JournalFrame_saveButton_actionAdapter(this));
this.setTitle("Journal");
gridLayout3.setColumns(1);
gridLayout3.setRows(0);
this.getContentPane().add(datePanel, BorderLayout.NORTH);
this.getContentPane().add(radioPanel, BorderLayout.WEST);
this.getContentPane().add(textAreaPanel, BorderLayout.CENTER);
this.getContentPane().add(buttonPanel, BorderLayout.EAST);
entryType.add(personalButton);
entryType.add(businessButton);
datePanel.add(dateLabel);
datePanel.add(dateField);
radioPanel.add(personalButton, null);
radioPanel.add(businessButton, null);
textAreaPanel.add(entryArea, null);
buttonPanel.add(clearButton, null);
buttonPanel.add(saveButton, null);
this.getContentPane().add(statusPanel, BorderLayout.SOUTH);
statusPanel.add(status, null);
this.pack();
setDefaultCloseOperation(EXIT_ON_CLOSE);
private void saveEntry() throws IOException{
if( personalButton.isSelected())
String file = "Personal.txt";
BufferedWriter bw = new BufferedWriter(new FileWriter(file,true));
entryArea.getText();
bw.write("Date: " + dateField.getText());
bw.newLine();
bw.write(entryArea.getText());
bw.newLine();
bw.flush();
bw.close();
status.setText("Journal Entry Saved");
else if (businessButton.isSelected())
String file = "Business.txt";
BufferedWriter bw = new BufferedWriter(new FileWriter(file,true));
bw.write("Date: " + dateField.getText());
bw.newLine();
bw.write(entryArea.getText());
bw.newLine();
bw.flush();
bw.close();
status.setText("Journal Entry Saved");
void clearButton_actionPerformed(ActionEvent e) {
dateField.setText("");
entryArea.setText("");
status.setText("");
void saveButton_actionPerformed(ActionEvent e){
try{
saveEntry();
}catch(IOException error){
status.setText("Error: Could not save journal entry");
void personalButton_actionPerformed(ActionEvent e) {
class JournalFrame_clearButton_actionAdapter implements java.awt.event.ActionListener {
JournalFrame adaptee;
JournalFrame_clearButton_actionAdapter(JournalFrame adaptee) {
this.adaptee = adaptee;
public void actionPerformed(ActionEvent e) {
adaptee.clearButton_actionPerformed(e);
class JournalFrame_saveButton_actionAdapter implements java.awt.event.ActionListener {
JournalFrame adaptee;
JournalFrame_saveButton_actionAdapter(JournalFrame adaptee) {
this.adaptee = adaptee;
public void actionPerformed(ActionEvent e) {
adaptee.saveButton_actionPerformed(e);
class JournalFrame_personalButton_actionAdapter implements java.awt.event.ActionListener {
JournalFrame adaptee;
JournalFrame_personalButton_actionAdapter(JournalFrame adaptee) {
this.adaptee = adaptee;
public void actionPerformed(ActionEvent e) {
adaptee.personalButton_actionPerformed(e);
public class JournalApp {
public static void main(String args[])
JournalFrame journal = new JournalFrame();
journal.setVisible(true);
}Bet you're trying "java JournalFrame" when you need to "java JournalApp".
Couple pointers toward good code.
1) Use white space (extra returns) to separate your code into logical "paragraphs" of thought.
2) Add comments. At a minimum a comment at the beginning should name the file, state its purpose, identify the programmer and date written. A comment at the end should state that you've reached the end. In the middle, any non-obvious code should be commented and closing braces or parens should have a comment stating what they close (if there is non-trivial separation from where they open).
Here's a sample:
// JournalFrame.java - this does ???
// saisoft, 4/18/03
// constructor
private void jbInit() throws Exception {
this.getContentPane().setLayout(borderLayout1);
radioPanel.setLayout(gridLayout1);
statusPanel.setLayout(flowLayout1);
textAreaPanel.setLayout(gridLayout2);
buttonPanel.setLayout(gridLayout3);
personalButton.setSelected(true);
personalButton.setText("Personal");
personalButton.addActionListener(new JournalFrame_personalButton_actionAdapter(this));
businessButton.setText("Business");
status.setText("");
entryArea.setText("");
entryArea.setColumns(10);
entryArea.setLineWrap(true);
entryArea.setRows(30);
entryArea.setWrapStyleWord(true);
} // end constructor
// end JournalFrame.java3) What would you expect to gain from that inner class? It might be more cool, but would it be more clear? I give the latter (clarity) a lot of importance. -
I am trying to manually make a drawing program similar to this one
http://javafx.com/samples/Draw/
However I am running into issues involving inner classes and finals.
"local variable size is accessed from within inner class; needs to be declared final"
It wants me to make either SIZE or size a final. However once final, I can't change the variable.
I have often used the variable in a for loop to assign a value(though maybe it was a bad practice?) however I am not sure the best way to handle this.
Any suggestions?
Thanks!
int SIZE = 1; //somewhere else
for( int size = 0 ; size < 5 ; size++){
Circle circle = new Circle(D/Padding);
circle.setOnMousePressed(new EventHandler<MouseEvent>(){
public void handle(MouseEvent me){
SIZE = size;
);edit:
I am well aware this isnt neccesarily a javafx specific thing, but more of a general java poor programming knowledge.
I also know that the mouseadapter is an anonymous class and can only access final.
I am just looking for any suggestions on how to best handle this.
Edited by: namrog on Jul 5, 2011 10:51 AM
Edited by: namrog on Jul 5, 2011 10:59 AMnamrog wrote:
I am trying to manually make a drawing program similar to this one
http://javafx.com/samples/Draw/
However I am running into issues involving inner classes and finals.
"local variable size is accessed from within inner class; needs to be declared final"
It wants me to make either SIZE or size a final. However once final, I can't change the variable.Yes, that's the point. If a local variable is to be used by an instance of a nested class, that nested instance can live on long after the local variable goes out of scope. So it needs its own, separate copy of the variable. However, since, as far as we are concerned, there is only one variable, that variable needs to be final, so that there will not be issues with keeping the two copies' values coherent.
I have often used the variable in a for loop to assign a value(though maybe it was a bad practice?) however I am not sure the best way to handle this.
Any suggestions?Create a final variable and copy the value of your non-final variable to it.
int nonFinal =...;
final int theFinalCopy = nonFinal;
new Whatever() {
void doStuff() {
doSomething(theFinalCopy);
} -
How can I say my inner class uses the same type as it's genericised host class?
Should I just not declare a "generic" type in the inner class?
The code
public class LinkedList<E> implements java.util.List<E>
... code omitted for brevity ...
* An internal implementation of java.util.Iterator.
private class Iterator<E> implements java.util.Iterator<E> {
protected Node<E> current;
public Iterator() {
this.current = head; // error here
... code omitted for brevity ...
produces the compiler error
C:\Java\home\src\linkedlist\LinkedList.java:59: incompatible types
found : linkedlist.LinkedList.Node<E>
required: linkedlist.LinkedList.Node<E>
this.current = head;
^I understand the meaning of the compiler error... it's effectively saying that "E" is not the same type within in the Iterator class as it is in the parent LinkedList class... What I don't understand is how to make E the same type within the Iterator... if I just leave the <E> off of Iterator<E> then it throws "unchecked operation" warnings... do I just have to put up with these warnings... but no that can't be right because java.util.LinkedList has an iterator and it's not throwing unchecked operation compiler warnings... so there has to be a way...
Thanx all. Keith.One more dumbshit question...
Is there a way to do this without the warnings OR the @SuppressWarnings({"unchecked"})
* Returns the index of the last occurrence of the specified element in this
* list, or -1 if this list does not contain the element.
//@SuppressWarnings({"unchecked"})
public int lastIndexOf(Object object) {
int i = 0;
int last = -1;
for(Node<E> node=this.head.next; node!=null; node=node.next) {
if (node.item.equals((E) object)) {
last = i;
i++;
return(last);
produces the warning
C:\Java\home\src\linkedlist\LinkedList.java:313: warning: [unchecked] unchecked cast
found : java.lang.Object
required: E
if (node.item.equals((E) object)) {
^... remembering that List specifies +public int lastIndexOf(Object object);+ as taking a raw Object, not E element, as I would have expected.
Thanx all. Keith. -
State pattern and inner classes
Hi,
I'm implementing the standard state design pattern. I have an object and that object delegates certain operations to various state classes. My problem is the state classes may need private information of the context class. So I can think of a few designs:
* make the private info of the context class default so the state classes can access them
* make appropriate getters for the private info (so again the state classes can access them
* pass the private info to the state classes
* make the state classes inner classes so the state classes have access to private info with any change
I would think the inner class solution is best. any comments? thanks.I prefer inner classes for state objects.
But if they become very big, maintenance can be an issue and other approaches can be more appropriate.
JCG -
Javadoc, generics and inner classes
I have implemented a generic class DiGraph with inner classes Vertex and Edge:
public class DiGraph<V,E> implements Iterable<DiGraph<V,E>.Vertex> {
public Vertex addVertex(V value) {...}
public Iterator<DiGraph<V,E>.Vertex> iterator() {... }
public class Vertex implements Iterable<Edge> {
V value;
public class Edge {
E value;
}When i run Javadoc it yields the following documentation of the class DiGraph :
public class DiGraph extends Object implements Iterable<DiGraph.Vertex>What I expected was
public class DiGraph extends Object implements Iterable<DiGraph<V,E>.Vertex>In a similar way the method addVertex appears as:
public DiGraph.Vertex addVertex(V value)instead of
public DiGraph<V,E>.Vertex addVertex(V value)This is very confusing, because if I create a graph
DiGraph<String,Integer> myGraph and the use e.g., the method addVertex I must write:
DiGraph<String,Integer>.Vertex v = myGraph.addVertex("a");Can anyone explain why the documentation lacks <V,E> ?One more dumbshit question...
Is there a way to do this without the warnings OR the @SuppressWarnings({"unchecked"})
* Returns the index of the last occurrence of the specified element in this
* list, or -1 if this list does not contain the element.
//@SuppressWarnings({"unchecked"})
public int lastIndexOf(Object object) {
int i = 0;
int last = -1;
for(Node<E> node=this.head.next; node!=null; node=node.next) {
if (node.item.equals((E) object)) {
last = i;
i++;
return(last);
produces the warning
C:\Java\home\src\linkedlist\LinkedList.java:313: warning: [unchecked] unchecked cast
found : java.lang.Object
required: E
if (node.item.equals((E) object)) {
^... remembering that List specifies +public int lastIndexOf(Object object);+ as taking a raw Object, not E element, as I would have expected.
Thanx all. Keith. -
Which one is better static inner classes or inheritance ?
Hi,
Consider following scenario,
Class A does some database related work and Class B,C,D has more specific tasks for specific databases. For now B,C,D has more static information like driver name etc.
1. I can either make class B,C,D as static inner classes OR
2. classes B,C,D can extend class A.
Case 1. makes it more flexible, if in future, B,C,D needs more than static methods.
Case 2. can avoid complexity and cost of instantiating differnt objects based on differnt scenarios.
Which approache is better in both ?
ThanksYes, I have seen abstract factory pattern , rather I have implemeted it at one place and in case 1. using abstract factory pattern is the way to initialize all classes.But my question is if I make all subclasses as a static inner classes, will it be better or efficient approach as compare to abstract factory pattern.Because Abstract factory patter adds more complications in code in turn it provides more flexibility.
-
How to create an object of inner class
hi i don't know how to create an object of an inner class..
i got something like
class Abc{
private class Abcd {
like this and i want to create an object of Abcd so that i can use some of method
there..
i think i should create the outter class object first right? but not sure
the syntax.. i tried something like
Abc.Abcd justTry = new Abc.Abcd()
something like this..but not work..
help me plz. ...If the nested class (that's not technically an inner
class you have there) is not static, then you can't
refer to it with OuterClassName.InnerClassName any
more than you can refer to any other member--method
or variable--with ClassName.staticMember.
You need an instance.
It's been a while since I've created an instance of a
non-static nested class from outside that clsas, but
I think it's something like this: Outer outer = new Outer();
outer.Inner inner = new outer.Inner();
Actually, I think it is this:
Outer outer = new Outer();
outer.Inner inner = outer.new Inner();Can't test it now though, gotta go to Taco John's for TACO TUESDAY!!!!
Gotta love them crunchy shell bean tacos!!! -
Help,about why we use inner class?
Hi,
when i read "java Tutorial"
i found there is one chapter about inner class .
i copy it down as follow.
the context is about there is a class Stack, and this class want to implement some function of interface Iterator,but as the book said
we should not let class Stack implement the Iterator directly, we should add a inner class inside the Stack .
i know it's very import ,but i still can not understand the reason why add a inner class here.
hope somebody can explain it a little more for me or give an example.
thank in advance!
Iterator defines the interface for stepping once through the elements within an ordered set in order. You use it like this:
while (hasNext()) {
next();
The Stack class itself should not implement the Iterator interface, because of certain limitations imposed by the API of the Iterator interface: two separate objects could not enumerate the items in the Stack concurrently, because there's no way of knowing who's calling the next method; the enumeration could not be restarted, because the Iterator interface doesn't have methods to support that; and the enumeration could be invoked only once, because the Iterator interface doesn't have methods for going back to the beginning. Instead, a helper class should do the work for Stack.
The helper class must have access to the Stack's elements and also must be able to access them directly because the Stack's public interface supports only LIFO access. This is where inner classes come in.
Here's a Stack implementation that defines a helper class, called StackIterator, for enumerating the stack's elements:
public class Stack {
private Object[] items;
//code for Stack's methods and constructors
not shown
public Iterator iterator() {
return new StackIterator();
class StackIterator implements Iterator {
int currentItem = items.size() - 1;
public boolean hasNext() {
public Object next() {
public void remove() {
or you can visit here
http://java.sun.com/docs/books/tutorial/java/javaOO/innerclasses.htmlthe context is about there is a class Stack, and this
class want to implement some function of interface
Iterator,but as the book said
we should not let class Stack implement the Iterator
directly, we should add a inner class inside the
Stack .Simply because the implementation of the Iterator is nobody's business. By declaring it to be a private inner clss, nobody will ever know about it and only see the Iterator interface. -
Hello to all
I have one doubt regarding eventhandling. Consider i am having one class named outer which extends applet and with in outer class i am having one class inner which extends panel.
Now when i try to add the inner class object in action performed of outer
class it doesnt get added. How to overcome this.
Eventhough sometimes it gets added it shouldnot appear for the first time. After resizing the window only it gets displayed.
How to over come this.
This is my coding
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Test extends JApplet implements ActionListener{
JButton b1;
Container c;
public void init()
c=getContentPane();
b1=new JButton("First");
c.add(b1,BorderLayout.NORTH);
b1.addActionListener(this);
public void actionPerformed(ActionEvent ae)
System.out.println("Working");
c.add(new panel());
class panel extends JPanel
int a=5;
JLabel l=new JLabel("ADSF");
public panel()
add(new JButton("ASDFASDFs"));
add(l);
/*public void paint(Graphics g)
g.drawString("ASDFASDF123123123123",20,20);
}You could try being more specific when you add ie
c.add(new panel(), BorderLayout.CENTER); -
ActionListener and Inner Class Issue
When I add ".addActionListener()" to buttons and create an inner class to listen/handle the action, my main class does not display the GUI. If I remove the ".addActionListener()" from the buttons and the inner class, the GUI displays. Below is my code. Anyone know what is wrong with my code?
package projects.web;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
public class AppletGUI{
// JButtons
JButton addButton = new JButton("Add");
JButton removeButton = new JButton("Remove");
JButton saveButton = new JButton("Save");
JButton cancelButton = new JButton("Cancel");
// JPanels
JPanel containerPanel = new JPanel();
JPanel optionsPanel = new JPanel();
JPanel thumbnailPanel = new JPanel();
JPanel selectionPanel = new JPanel();
// JScrollPane
JScrollPane thumbnailScroll;
public AppletGUI(JRootPane topContainer){
// Add actionListener
addButton.addActionListener(new ButtonHandler());
removeButton.addActionListener(new ButtonHandler());
saveButton.addActionListener(new ButtonHandler());
cancelButton.addActionListener(new ButtonHandler());
// Set border layout
containerPanel.setLayout(new BorderLayout());
// Add buttons to target panels
optionsPanel.add(addButton);
optionsPanel.add(removeButton);
selectionPanel.add(saveButton);
selectionPanel.add(cancelButton);
// Set size and color of thumbnail panel
thumbnailPanel.setPreferredSize(new Dimension (600,500));
thumbnailPanel.setBackground(Color.white);
thumbnailPanel.setBorder(new LineBorder(Color.black));
// Add thumbnail panel to scrollpane
thumbnailScroll = new JScrollPane(thumbnailPanel);
// Set background color of scrollPane
thumbnailScroll.setBackground(Color.white);
// Add subpanels to containerPanel
containerPanel.add(optionsPanel, BorderLayout.NORTH);
containerPanel.add(thumbnailScroll, BorderLayout.CENTER);
containerPanel.add(selectionPanel, BorderLayout.SOUTH);
// Add containerPanel to rootPane's contentPane
topContainer.getContentPane().add(containerPanel);
} // end constructor
class ButtonHandler implements ActionListener{
public void actionPerformed(ActionEvent event){
new FileBrowser();
} // end actionPerformed method
} // end inner class ActionHandler
} // end AppletGUI class package projects.web;
import java.awt.*;
import java.io.*;
import javax.swing.*;
import javax.swing.filechooser.*;
public class FileBrowser{
JFileChooser fileChooser = new JFileChooser();
public FileBrowser(){
int fileChooserOption = fileChooser.showOpenDialog(null);
} // end constructor
} // end class fileBrowserEncephalopathic wrote:
Dan: When it doesn't display, what happens? Do you see any error messages? Also, please take a look at your other thread in this same forum as it has relevance to our conversations in the java-forums.org about whether to add GUIs to root containers or the other way around. /PeteI fiddled with the code some more and it seems that the problem is the inner code. When I changed from the inner class to the main class implementing ActionListener and had the main class implement the actionPerformed method, the GUI displayed and JFileChooser worked as well. I've add this version of the code at the bottom of this message.
To answer your question: When it doesn't display, what happens? -- The web page loads and is blank. And there are no error messages.
I took a look at the other thread is this forum (the one relates to our conversation in the other forum); the problem may be the way I've add the GUI. I'll try it the other way and see what happens.
Thanks,
Dan
package projects.web;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
public class AppletGUI implements ActionListener{
// JButtons
JButton addButton = new JButton("Add");
JButton removeButton = new JButton("Remove");
JButton saveButton = new JButton("Save");
JButton cancelButton = new JButton("Cancel");
// JPanels
JPanel containerPanel = new JPanel();
JPanel optionsPanel = new JPanel();
JPanel thumbnailPanel = new JPanel();
JPanel selectionPanel = new JPanel();
// JScrollPane
JScrollPane thumbnailScroll;
public AppletGUI(JRootPane topContainer){
// Add actionListener
addButton.addActionListener(this);
removeButton.addActionListener(new ButtonHandler());
saveButton.addActionListener(new ButtonHandler());
cancelButton.addActionListener(new ButtonHandler());
// Set border layout
containerPanel.setLayout(new BorderLayout());
// Add buttons to target panels
optionsPanel.add(addButton);
optionsPanel.add(removeButton);
selectionPanel.add(saveButton);
selectionPanel.add(cancelButton);
// Set size and color of thumbnail panel
thumbnailPanel.setPreferredSize(new Dimension (600,500));
thumbnailPanel.setBackground(Color.white);
thumbnailPanel.setBorder(new LineBorder(Color.black));
// Add thumbnail panel to scrollpane
thumbnailScroll = new JScrollPane(thumbnailPanel);
// Set background color of scrollPane
thumbnailScroll.setBackground(Color.white);
// Add subpanels to containerPanel
containerPanel.add(optionsPanel, BorderLayout.NORTH);
containerPanel.add(thumbnailScroll, BorderLayout.CENTER);
containerPanel.add(selectionPanel, BorderLayout.SOUTH);
// Add containerPanel to rootPane's contentPane
topContainer.getContentPane().add(containerPanel);
} // end constructor
public void actionPerformed(ActionEvent event){
new FileBrowser();
} // end actionPerformed method
class ButtonHandler implements ActionListener{
public void actionPerformed(ActionEvent event){
new FileBrowser();
} // end actionPerformed method
} // end inner class ActionHandler
} // end AppletGUI class -
Inner Classes - when to use with Swing?
Hi again,
I was creating a GUI with JTabbedPane as content pane, while doing the single panes in the different tabs i started wondering about some design issues.
Let�s say you have a pane that is composed of 3 "subpanes" ( containing all the interaction components ). Should i write "normal" classes for each of the subpanes or is it more reasonable to define them as inner classes of the "main" panel - that�s at least what i thought because those 3 smaller panels are bound to the main panel for their lifetime...
Any design tips about inner classes and swing or even inner classes in general, i�d really appreciate.
ThxThe concept of inner classes design in java is (I hope) they provide 'composite aggregation' relation with the contained class.
Means that the (inner) class cannot exists alone and provide functionalities like other classes. Inner classes refer to the "contains" relationship in the UML.
The other regular associations say, having a value oject model to an UI are Structural Aggregation, means that the value object can be used in the UI and also separately.
For your case the inner classes are not suitable. You may have to find a suitable mechanism to get the individual tab panes. Probably use an interface to bridge the three tab panes and use an manager class, pass and id to the manager class and get the required Tabbed pane.
Thanks,
ananth
Hi again,
I was creating a GUI with JTabbedPane as content pane,
while doing the single panes in the different tabs i
started wondering about some design issues.
Let�s say you have a pane that is composed of 3
"subpanes" ( containing all the interaction components
). Should i write "normal" classes for each of the
subpanes or is it more reasonable to define them as
inner classes of the "main" panel - that�s at least
what i thought because those 3 smaller panels are
bound to the main panel for their lifetime...
Any design tips about inner classes and swing or even
inner classes in general, i�d really appreciate.
Thx
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