I've been looking around and I only found one answer which wasn't clear enough, to me at least.
I am building a very basic chat application with a GUI and I have separated the GUI from the connection stuff. Now I need to call one method from GUI in server class and vice versa. But I don't quite understand how to do it (even with "this"). Here's what a part of code looks like (this is a class named server_frame):
textField.addActionListener(
new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
try {
srv.sendData(arg0.getActionCommand());
} catch (Exception e) {
e.printStackTrace();
}
textField.setText("");
}
}
);
This is a code from server_frame, srv is an object from the other class (server) which contains sendData method, and I probably didn't define it correctly so hopefully someone could make a definition of it.
On the other side class server from which object srv was made contains method using JTextArea displayArea from server_frame in this code:
private void displayMessage(final String message){
sf = new server_frame();
SwingUtilities.invokeLater(new Runnable(){
public void run(){
sf.displayArea.append(message);
}
}
);
}
Yet again sf is an object made of server_frame and yet again probably missdefined :)
Hopefully that was clear enough, sadly I tried the searching but it just didn't give me the results I was looking for, if you need any more info I will gladly add it!
Thanks for reading,
Mr.P.
P.S. Please don't mind if I made terminology mishaps, I am still quite new to java and open to any corrections!
Some class must be building both of these objects--the GUI and the server--and it should make each aware of the other. For example, say the main class is ServerApplication. I'll use standard Java convention of starting class names with an uppercase letter for clarity.
class ServerApplication {
Server server;
ServerFrame gui;
public static void main(String []) {
server = new Server(...);
gui = new ServerFrame(server);
server.setGui(gui);
}
}
Each class should store the reference to the other as well.
class Server {
ServerFrame gui;
public void setGui(ServerFrame gui) {
this.gui = gui;
}
...
}
class ServerFrame extends JFrame {
Server server;
public ServerFrame(Server server) {
this.server = server;
}
...
}
I think you may be looking for the ClassName.this.methodName syntax. this in those actionlisteners refer to the anonymous class you created. If you used the above syntax you would be referencing the class that contains the anonymous class.
Or if you are looking for a private field in the class, you would do ClassName.this.privateField
Related
I decided to split the last part of that question here into a new question here: https://softwareengineering.stackexchange.com/questions/411738/extension-of-classes-where-to-put-behaviour-how-much-direct-access-is-allowe
If i have a lib and i want to use it, i wrote mostly a own class. This class has one method. In that there is the code how to instantiate the lib/framework. Sometimes there are a few more methods, with them i not only instantiate the class but use it. For example if i want to start a http-server i have there a start-method.
class Container
{
TheLib theLib;
public void init() //or a constructor
{
//some init of the theLib
}
public void start() //
{
theLib.doSomething(...)
theLib.doSomethingmore(...);
theLib.start(...);
}
//important!
public TheLib getTheLib()
{
return this.theLib; //after i started configured it and so on, i want of course use all methods,
which the lib have in some other parts in my application
}
}
But it seems not to be the best solution.
Are there any better solutions, that OO is?
Often i also use only one method, a own class for this seems to be here a big overhead?
Exposing the lib breaks encapsulation? Tell-Dont-Ask is also violated?
Everything depend on what you actually need or how you have access to your 'the lib' instance.
public class Container {
private TheLib theLib;
/* #1: Do you already created the instance before? */
public Container(TheLib theLib) {
this.theLib = theLib;
}
/* #2: Do you need to created the instance each time? */
public Container() {
this.theLib = new TheLib();
}
public void start() {
theLib.doSomething(...)
theLib.doSomethingmore(...);
theLib.start(...);
}
public TheLib getTheLib() {
return this.theLib;
}
public static void main(String[] args) {
/* #1 */
TheLib theLib = ...;
Container container = new Container(theLib);
/* #2 */
Container container = new Container();
/* Continue the flow of your program */
container.start();
container.getTheLib().doSomethingEvenMore();
}
}
Or maybe you actually need only one instance of your 'Container' class. In this case, you should look on how to make a singleton: Java Singleton and Synchronization
Anwser: Often i also use only one method, a own class for this seems to be here a big overhead?
Well, in Java, you cannot do formal programming like in C, so everything line of code that you write, or will be using, has to be in a class of some sort.
If your piece of code is small and don't really need an object, static function might do the work.
So I'm learning JavaFX programming and MVC. The control is also its own class and isn't integrated into the view (Which I've heard is one way to go at it). I want it to be separated from the view but because I'm trying to encapsulate everything and leave everything private with limited access to the controls/nodes, I find myself using methods to do almost anything inside of my object almost entirely when using event handlers in the control.
Example (Not an actual program, just wrote it here because I have no short examples.):
View:
public class SamplePane extends BorderPane {
private TextField tfScoreOne;
private Button btnScore, btnPenalty;
private int scoreOne;
public SamplePane() {
// Some constructor
}
public void giveScore() {
scoreOne++;
tfScoreOne.textProperty().setValue("Score: " + Integer.toString(scoreOne);
}
public void takeScore() {
scoreOne--;
tfScoreOne.textProperty().setValue("Score: " + Integer.toString(scoreOne);
}
}
public void btnScoreAddHandler(EventHandler<ActionEvent> handler) {
btnOneAdd.setOnAction(handler);
}
public void btnPenaltyAddHandler(EventHandler<ActionEvent> handler) {
btnOneAdd.setOnAction(handler);
}
Control:
public class SampleController {
public ModuleSelectionController() {
// Some contorller stuff again
samplePaneObj.btnScoreAddHandler(btnScoreHandler);
samplePaneObj.btnPenaltyAddHandler(btnScoreHandler);
}
private class btnScoreHandler implements EventHandler<ActionEvent> {
public void handle(ActionEvent arg0) {
samplePaneObj.giveScore();
}
}
private class btnPenaltyHandler implements EventHandler<ActionEvent> {
public void handle(ActionEvent arg0) {
samplePaneObj.takeScore();
}
}
}
This is mostly pseudocode so forgive me if there are any errors but do you get the point? It seems very arbitrary to just be calling methods but without passing the TextField in the example its hard to not do everything without a method doing all the work.
But is that decoupled enough for MVC? I don't really wanna break encapsulation is the main issue so I can't make the controls public and operate on them directly in the controller.
Is this all just normal? I want to make sure I'm grasping it right.
There is too much that could be said about this here. I'd advise you to have a look at a JavaFX application framework and read its documentation. I learned a lot from it. E.g., have a look here: https://github.com/sialcasa/mvvmFX
Don't make the mistake and try to derive some implementation patterns yourself from all the hello world examples out there on the internet. They all don't teach you how things should be done so that they scale well for real-world projects.
I'm very new to Java and I'm setting myself the challenge on writing a Caesar shift cipher decoder. I'm basically trying to clear a JTextArea from another class. I have two classes, a GUI class called CrackerGUI and a shift class. The JtextArea is in the GUI class along with the following method:
public void setPlainTextBox(String text)
{
plainTextBox.setText(text);
}
The GUI class also has a clear button with the following:
private void btnClearActionPerformed(java.awt.event.ActionEvent evt) {
Shift classShift = new Shift();
classShift.btnClear();
}
Lastly i have the method in the shift class to clear the JTextArea.
public class Shift extends CrackerGUI {
public void btnClear()
{
CrackerGUI gui = new CrackerGUI();
gui.setPlainText(" ");
System.out.println("testing");
}
}
The testing text is printing out to console but the JTextArea wont clear. I'm not sure as to why :). I am sure it's a very simple mistake but it has me baffled. Any help would be appreciated.
Thank you in advance.
You're misusing inheritance to solve a problem that doesn't involve inheritance. Don't have Shift extend CrackerGUI and don't create a new CrackerGUI object inside of the btnClear() method since neither CrackerGUi is the one that's displayed. Instead have Shift hold a reference to the displayed CrackerGUI object and have it call a public method of this object.
e.g.,
public class Shift {
private CrackerGUI gui;
// pass in a reference to the displayed CrackerGUI object
public Shift(CrackerGUI gui) {
this.gui = gui;
}
public void btnClear() {
//CrackerGUI gui = new CrackerGUI();
gui.setPlainText(" ");
System.out.println("testing");
}
}
You also should probably not be creating new Shift objects in your GUI's actionPerformed methods, but rather use only one Shift object that is a class field.
The btnClear method clears the text area of a new CrackerGUI instance. It's like if you wanted to clear a drawing on a sheet of paper by taking a new blank sheet and clearing it. The original sheet of paper will keep its drawing.
You need to pass the gui instance to your Shift:
public class Shift {
private CrackerGUI gui;
public Shift(CrackerGUI gui) {
this.gui = gui;
}
public void btnClear() {
this.gui.setPlainText(" ");
}
}
and in the CrackerGUI class :
private void btnClearActionPerformed(java.awt.event.ActionEvent evt) {
Shift classShift = new Shift(this);
classShift.btnClear();
}
Assuming CrackerGUI is your GUI, you should have the following instead:
public class CrackerGUI {
public void setPlainTextBox(String text)
{
plainTextBox.setText(text);
}
public void btnClear()
{
setPlainTextBox("");
System.out.println("testing");
}
}
One last thing, never make your GUI elements public! You should ask the GUI to clear itself and leave that knowledge of clearing elements hidden inside it.
You could try using static methods, as you would end up creating a new gui, then displaying that one, in stead of the current one already displayed.
This would require the parent class to be static too, which may cause errors in some of your methods, just a heads up.
Or else, you could create your own setText method:
void setText(JTextField t, String s){
t.setText(s);
}
that may enable you to directly edit components in the current GUI.
I can't get my head round this one. I've tried to adhere to the MVC pattern for the first time and now have difficulties accessing the source of an ActionEvent because the ActionListener is located in a different class. But let the code do the talking...
In the "view":
// ControlForms.java
...
private JPanel createSearchPanel() throws SQLException {
...
comboBoxCode = new JComboBox(); // Field comboBoxCode -> JComboBox()
SwingUtilities.invokeLater(new Runnable() {
public void run() {
AutoCompleteSupport<Object> support = AutoCompleteSupport.install(
comboBoxCode, GlazedLists.eventListOf(jnlCodeArray));
}
}); // Auto-Complete comboBox from GlazedLists
...
public void setComboListener(ComboListener comboListener) {
comboBoxCode.addActionListener(comboListener);
}
...
}
Then, in what I term the controller, I have two different classes:
// Controller.java
public MyController() throws SQLException {
...
addListeners();
}
...
private void addListeners(){
View view = getView();
getView().getControlForm().setComboListener(new ComboListener());
}
and
public class ComboListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
System.out.println("ComboBox listened to! e = " + e.toString());
}
}
Now, e obviously doesn't give the name of the variable (which at the moment I wish it would), so I cannot if test for e.getSource().
My question is thus: is there either a) a way to query (via if for example) the source of e, or b) a less complicated way to get to the variable name?
Many, many thanks in advance for your insights and tips!
Why do you need the name of the variable? Why can't you do the event handling like this
public class ComboListener implements ActionListener
{
public void actionPerformed(ActionEvent e)
{
JComboBox source = (JComboBox)e.getSource();
//do processing here
}
}
I'd think that if you need to do processing according the variable name, obviously you need different listeners for different combo boxes.
Generally, there are only two situations in which you should use a listener like that: a) you're going to handle a certain event the same way for a bunch of objects, or b) you're only going to use the listener for one object. In the latter case, I'd prefer handling the event locally anyway.
That said, the direct answer to your question is: you shouldn't have to check inside your ActionListener implementation to see whether the appropriate object is the source of the event; you should simply only add the ActionListener to that one object.
One final note: without knowing the specifics of your architecture... generally, MVC will treat all event handling as part of the View (it reduces coupling) and the View will pass commands or method calls or your own events (i.e., not Swing's) to the Controller.
I'm using netbeans to program something with a user interface...
I hava a main class that named "NewJFrame.java"(A) and one more class
that named "NewClass.java"(B). Class A is extended to class B like this:
public class NewClass extends NewJFrame{
...
}
Contents of ClassA are public static like this:
public static javax.swing.JTextField TextBox1;
I also has a button in classA .So when I click the button, it will call a function
from the classB and that function needs to edit TextBox1's text...
Here is whats going on when I click the button:
private void jToggleButton1ActionPerformed(java.awt.event.ActionEvent evt) {
String Str1;
NewClass nc = new NewClass();
Str1=nc.call();
}
Here is the funcion in ClassB:
public String call()
{
String Str;
Str = TextBox1.getText();
TextBox1.setText(Str + "1"); //This part isn't work.
JOptionPane.showConfirmDialog(null,Str,"22222222",JOptionPane.PLAIN_MESSAGE);
return Str;
}
So I can read the text of TextBox1 and show it in a messagebox but cannot edit his text.
If I put this code in main class it works perfectly but in another class it doesn't work.
Can someone help me to reslove this problem?
(I'm using netbeans 6.9.1)
I Just Trying to use some another class to add my code because I dont want all the codes stay in same file this is not usefull... Come on someone needs to know how to do that you can't be writing all the codes in a *.java file right?
The problem you are facing has nothing to do with NetBeans IDE,
you will face the same problem with any IDE for this code.
One way of achieving this is by aggregating the NewJFrame class in the NewClass
instead of extending it:
Let me exlplain with some code:
public class NewClass {
private NewJFrame frame = null;
public NewClass(NewJFrame frame) {
this.frame = frame;
}
public String call()
{
String text;
text = frame.TextBox1.getText();
frame.TextBox1.setText(text + "1"); //This will work now.
JOptionPane.showConfirmDialog(null,text,"22222222",JOptionPane.PLAIN_MESSAGE);
return text;
}
}
Here we will receive a reference to the calling JFrame class and will use fields
defined in that class.
private void jToggleButton1ActionPerformed(java.awt.event.ActionEvent evt) {
String Str1;
NewClass nc = new NewClass(this); // see the parameter we are passing here
Str1=nc.call();
}
When we create an object of class NewClass we will pass the reference of the
currently calling NewJFrame object
This will work check it.
Now coming to why your code is not working. When NewClass is extending NewJFrame
and when you create a new object of NewClass class it contains a separate
copy of the NewJFrame which is different from the calling NewJFrame reference hence
the field is getting set in another JFrame and not what you wanted.
with regards
Tushar Joshi, Nagpur
AFAIK Netbeans prevents you from editing by hand GUI's and behaves diferrently depending on strange issues like the one you have... but it was months ago, I dont know if current version sucks that much yet.
I really don't understand why you are forcing yourself to use a new class for this? Even if you NEED to, I don't understand why NewClass extends NewJFrame since you are only creating an instance to call a method that has nothing to do with GUI.
I think creating NewClass isn't necessary. Writing all the code in one class isn't bad by itself. This really depends on MANY factors: how much is "all the code"? Does it make sense to separate responsibilities? Etc, etc...
So make the JTextField and JButton NOT static and NOT public, and simply do everything in there:
private void jToggleButton1ActionPerformed(java.awt.event.ActionEvent evt) {
String str = TextBox1.getText();
TextBox1.setText(str + "1"); //This part isn't work.
JOptionPane.showConfirmDialog(null,Str,"22222222",JOptionPane.PLAIN_MESSAGE);
}
P.S.: variable names are start in lowercase: String str, not String Str.
I Found a solution. I'm throwing the contents whereever I'll use. Here is an Example:
Main class:
private void formWindowOpened(WindowEvent evt) {
Tab1Codes tc1 = new Tab1Codes();
if(!tc1.LockAll(TabMenu1))
System.exit(1);
tc1.dispose();
}
Another class where I added some of my codes:
public boolean LockAll(javax.swing.JTabbedPane TabMenu){
try
{
TabMenu.setEnabledAt(1, false);
TabMenu.setEnabledAt(2, false);
TabMenu.setEnabledAt(3, false);
TabMenu.setEnabledAt(4, false);
}catch(Exception e)
{
JOptionPane.showConfirmDialog(null, "I can't Lock the tabs!",
"Locking tabs...",
JOptionPane.PLAIN_MESSAGE,
JOptionPane.ERROR_MESSAGE);
return false;
}
return true;
}
So, I can edit the contents in another class but it's little useless to send every content I want to read and edit.
If someone knows any short way please write here.