I have read many different topics and information sources but I can't really understand the differences of containers in java I know JPanel, JFrame and Container are similar and should be used at different levels within the construction of a program and I know there is JWindow and acts relatively the same. I am fairly new to programming so I am just unfamiliar with the setup. Here is what I have found out/assumed about each one, please correct me if i'm wrong.
JPanel is for the integration between JFrame or a Container typically separating different sections for labels, buttons, sliders etc...
JFrame acts as a receiver of JPanels and can construct them based on instructions from the coder, JFrame can also take the same labels, buttons, sliders etc....
Container is the same as JFrame though I am assuming container is a parent of JFrame.
I'm unsure of JWindow I just found out about this one.
Both JPanel and JFrame are Containers, yet more specialized for specific purposes. And yes, you have to assemble them correctly so they act as your user interface.
But as Container does not do much on it's own you probably never put that into your UI directly. Use it as base class to construct more specialized other classes.
To move along get some simple example running, you could follow the Java Tutorials.
Related
I have seen a program and was hoping to replicate one feature of it in my program. The program is a flashcard app, and when you create a new deck it adds another section to the homescreeen. I will attach images. I would love some advice on how to do this.
One of possible way is to use correct layouts, here is examples. Using this you may dynamically add any components (labels, images, buttons etc.) into your JPanel (I recommend to use JPanel as main container of all components instead of JFrame that should be one and just contain your JPanel).
I'm having some troubles designing the architecture of an application I'm trying to develop. I'm working on JAVA, and I started working on this application because I want to deepen my overall knowledge of JAVA, architectures and patterns. I want to follow the guidelines to make a reusable, low coupled application, like it should be. The application has only one JFrame, but inside it there are several JPanels, each one representing a module of the application.
The question is: in JAVA Swing, how to implement an appropriate MVC pattern?
I struggle on how to understand the way it should be done.
Should I have a main Controller class, that holds references to all the other Controllers?
(I have an image to demonstrate this, here: https://docs.google.com/file/d/0B7tBdn5slIFeY2FoSmxESTREQ1k/edit?usp=sharing)
And in this case, should all the events that require changing the module that is being presented redirect to the main Controller?
Or should I just couple the JFrame with the Controllers of the application, and communicate directly with them?
Basically, I would like to know if i need to have a class that 'manages' all the others.
I have already read several explanations, and different opinions, but I believe this is a little more specific.
Hope I have made myself clear (and hope as well that my explanation is better than my drawing :)).
EDIT:
a sample of the application usage:
One (an only one) JFrame throughout all the lifecycle of the application;
the menu will be on the left side, as in BorderLayout.WEST;
the current module of the application will be in the center, as in BorderLayout.CENTER;
when the user presses one button of the menu, the corresponding module is loaded into the BorderLayout.CENTER;
Should the menu (View) have it's own Controller, and this Controller communicate with the JFrame? And the JFrame load the new module into it's Layout? Or should the JFrame have its own Controller (or Model, as Gilbert Le Blanc said)?
I know this may seem to specific, or easy to understand, but everytime I think of an desktop application, I struggle to understand this.
When you have an application with a GUI, the GUI model becomes the application view. The application interacts with the GUI through the GUI model.
Or should I just couple the JFrame with the Controllers of the application, and communicate directly with them?
This is what I've done. I've packaged the controller classes together, but I've never created one main controller class.
I keep the GUI controller classes in a separate package from any other application controller classes, like the data access objects.
I usually put each JPanel in its own class, but I wouldn't call that a requirement. The JFrame has its own class, although the instance of the JFrame and the instance of the GUI model are passed to almost all of the GUI components. This makes menu actions possible.
This Traffic Signal GUI article goes over the basics of how to code a very simple GUI.
Edited to respond to the changes in the question.
The GUI controller is separate from the GUI model. The GUI model contains all of the data elements that make up your GUI. Strings for JTextFields, DefaultTableModels for JTables.
Based on your application design, I'd recommend that you create a Java class for every JPanel that you want to put in the center of your application. Your JFrame will control which JPanel is displayed, based on the menu. I'd also suggest that you look at the JTabbedPane which uses a different user interface to accomplish the task of choosing which panel to work with.
Assuming you're going with the menu on the left, each menu option (toggling JButton?) will have it's own controller method or class. These controllers have to have an instance of the JFrame so the controller can call the method in the JFrame class that puts the appropriate panel in the center of the display. The controller decides which method to call, but the methods themselves are a part of the JFrame class.
I've been talking about JFrame and JPanel classes. It's important that you use composition rather than inheritance to build these classes. The JFrame class contains a JFrame. It does not extend JFrame. The only time you extend a Swing component is when you want to override a component method.
As discussed here, Swing components use a separable model architecture with the model and view loosely coupled using the observer pattern. Not every GUI control has to be part of your application's controller. Using an ActionListener, such as Action, is particularly convenient for encapsulating application functionality.
Addendum: I'd use CardLayout, illustrated here to switch panels. Note how the Action handlers can be used with buttons, menus, combos, toolbars, etc. Each card's content can have it's own implementation of the MVC pattern, separate from the others. Use a PropertyChangeEvent, seen here, for communication between components.
In general, Swing components, e.g. buttons and tables, already listen to their respective models, leaving you to focus on your application's data model and its listening views. Conveniently, a Swing model, e.g. ComboBoxModel or TableModel`, can have more than one listener.
We are going to use Swing for our next project which will be a lightweight desktop app.
I've been reading the Swing tutorials on Oracle's website and have started to get the hang of it.
I was told that instead of switching JFrame I need to work within one JFrame and switch JPanels.
My questions to you would be the following.
Can I create the JPanel designs (or their templates) in design mode (WYSIWYG editor) and call jframe.setContentPane(nameOfJPanel) or do I do them programatically in code?
Secondly, how do I structure my code... If I dynamically add new JPanels and bind their events to an event handler.. all my logic and code will be in one HUGE class with tens of methods. I just don't know how to proceed and nowhere can I find an example with multiple (more than 6 let's say) panels on the internet.
To WYSIWYG or not WYSIWYG
This is a debatable question at the best of times.
I encourage all my junior developers to start out hand coding UIs as it teaches them important basics about how to use layout managers and how to handle compound layouts.
This tends to take longer as you need to verify the layout with each change.
I personally use the form editor in Netbeans for most of my general work, but will hand tweak UI's
Structure
Think about boundaries of responsibility, reuse and reduce strategies.
What you don't want is some huge master class that does EVERYTHING. It will be difficult to maintain and update (I live with this horror every day).
Instead, identify the distinct areas of responsibility and either use getters and setters or models to move the data around the application. The more you can decouple your code, the easier it will be to update and modify.
Identify like work and model it as interfaces and abstract classes where you can. Basically where ever you start thinking about coping code is probably a good indication that your design is off and you should consider implementing abstract classes to cover the overlap.
Take advantage of the Action API for replicating commonly used concepts (copy and paste is an example of this. You would want menu items, possible toolbar items and maybe even popup items, these can all be handled by the same Action class).
Separate the data from view. As I said before, take advantage of models. The data shouldn't care how it is collected or modified, only that it can be. Equally, the view shouldn't care about how the data is managed, only that it is.
If possible, define interfaces between the separate areas of your application. This way you can further decouple of the application and no one part becomes reliant on any one implementation (hello my world :P)
Don't be tempted to simply dig through a component hierarchy to gain access to that field, it will produce a nightmare if you need to change the code!!
The JFrame will be the main window of your app and the panels will be the brick composing it.
You should create each panel in its own class and you can arrange them by functionality in packages. You'll have panels for holding content of logical part of your application and panels that contains real stuff.
A logical panel could be the main view and the menu bar. An application panel would be a form, a menu, a canvas...
You'll have to put application panels inside logical panel and to change the content of the logical in response to users actions.
You should study how layouts work in order to compose the view inside the JFrame and to layout components inside panels.
For example the BorderLayout is a classic when defining the main area of an application:
- menu and toolbar on top
- browser on the left
- status bar at the bottom
- main panel on the center
You can use WYSIWYG editor, but avoid doing all design inside the same class. Else you'll have an horrible HUGE class. Create your panels in separate classes and compose them in your main view.
You can use empty panels as placeholder to help you create the structure of your application.
You'll have to bind your domain data to the view in order to not mix the two layer.
Bind means that you will write a way to go from a java bean to a form and the reverse.
Basic binding is handwritten, but some tools exists to do that.
If it is a small application, it is maybe better for you to handwrite everything.
Building a Swing application can be very tricky (you'll have to know about the event dispatch thread, layout management, event management, widgets (label are trivial, but JTable can be very complicated to handle);
I'll recommend to find a book about the topic, and to find some open source swing application in order to study how it structured, before you start your project.
This is how I organize my code:
class Panel1 extends JPanel{
//code for panel1 and its Components
}
class Panel2 extends JPanel{
//code for panel2 and its components
}
// and it follows.
class ApplicationFrame extends JFrame{
/// LOGIC to switch between panels
}
class Main{
//contains main() function
}
Any HAND-CRAFTED GUI code, is better than a COMPUTER GENERATED WYSIWYG -APP Code.
I have about 3 frames in my java swing application. What it the correct way how to handle with these frames? I mean some pattern or something else. Now I have always one class which represent frame and one class for panel which is main in this frame. Now I have defined frames as static variable and when I wanna hide them I call
classname.frameName.setVisible(false);
is this the correct solution?
Besides the (excellent) suggestions of a CardLayout or JFrame with multiple JDialog instances, here are some other strategies which might work singly or in combination, to collapse a variety of content panes into a single frame.
JDesktopPane/JInternalFames (Tut.).
JSplitPane (Tut.).
JTabbedPane (Tut.).
JLayeredPane, if you're feeling brave (Tut.).
JToolBar - floatable if needed (Tut.).
Different constraints of a JPanel in a nested layout.
There are probably more..
Of course, as Adamski pointed out, there are some further quirks to consider..
What if each frame has JMenuBars or JMenus?
Possibly combine them as sub-menus.
Take a look at a decent docking framework such as MyDoggy. This allows you to display all three components in a single JFrame, but is very flexible in that you can view the data side-by-side, resize and maximise components.
This design seems flawed. Instead of having multiple containers, you should use an appropriate layout manager. In this case, I recommend using CardLayout. This way, you would have a single container with multiple exchangeable views.
Controlling frames through static references seems to be a very fragile solution. What if the reference is null? What if the frame isn't in a completed state when setVisible() is called on it?
It would probably be a better idea to separate this logic out into a separate class and either have the frames register themselves to it , or construct everything up front.
I'm making a physics simulator for fun and I was looking up graphics tutorials when I tried to figure out the difference between all these J's.
Can somebody elaborate on them or perhaps provide a link to a helpful source?
Those classes are common extension points for Java UI designs. First off, realize that they don't necessarily have much to do with each other directly, so trying to find a relationship between them might be counterproductive.
JApplet - A base class that let's you write code that will run within the context of a browser, like for an interactive web page. This is cool and all but it brings limitations which is the price for it playing nice in the real world. Normally JApplet is used when you want to have your own UI in a web page. I've always wondered why people don't take advantage of applets to store state for a session so no database or cookies are needed.
JComponent - A base class for objects which intend to interact with Swing.
JFrame - Used to represent the stuff a window should have. This includes borders (resizeable y/n?), titlebar (App name or other message), controls (minimize/maximize allowed?), and event handlers for various system events like 'window close' (permit app to exit yet?).
JPanel - Generic class used to gather other elements together. This is more important with working with the visual layout or one of the provided layout managers e.g. gridbaglayout, etc. For example, you have a textbox that is bigger then the area you have reserved. Put the textbox in a scrolling pane and put that pane into a JPanel. Then when you place the JPanel, it will be more manageable in terms of layout.
JFrame and JApplet are top level containers. If you wish to create a desktop application, you will use JFrame and if you plan to host your application in browser you will use JApplet.
JComponent is an abstract class for all Swing components and you can use it as the base class for your new component. JPanel is a simple usable component you can use for almost anything.
Since this is for a fun project, the simplest way for you is to work with JPanel and then host it inside JFrame or JApplet. Netbeans has a visual designer for Swing with simple examples.
You might find it useful to lookup the classes on Oracle's website, for example:
https://docs.oracle.com/en/java/javase/15/docs/api/java.desktop/javax/swing/JFrame.html
There you can see that JFrame extends JComponent and JContainer.
JComponent is a a basic object that can be drawn. JContainer extends this so that you can add components to it. JPanel and JFrame both extend JComponent so that you can add things to them. JFrame provides a window, whereas JPanel is just a panel that goes inside a window.