So I have been coding Java for a few months now, and I have been using JOptionPane to display text and variables in my games. I want to upgrade to a single window like a normal game, but I want to only focus on simple buttons and text on the screen. I have tried learning JFrame and ActionListsner, but I failed to completley figure it out. JFrame really confused me.
My question is this: Is there an easier way beside JFrame to just have a window that I can have simple text, buttons and TextFields without the hassle of opening a bunch of windows with JOptionPane, making crap loads of ActionListeners with JFrame or having to get into GUI? If not, where can I find help on how to make games with JFrame?
You should be using a JFrame. Trust me, they aren't that hard to use. Using a JFrame, you could create multiple panels and switch between them using CardLayout.
Since you said you aren't sure about how JFrame works, I gave a short introduction to them at the end of this post. But first, lets first talk about how to solve your problem.
Switching Panels via CardLayout
When you want to switch whats being viewed in the window completely, you're gonna want an entirely different panel for that specific purpose (for example, one for Main Menu, and one for the game). CardLayout was created for this.
You specify a "deck" panel. This panel will hold all the other panels you wanna switch between (cards):
CardLayout layout = new CardLayout();
JPanel deck = new JPanel();
deck.setLayout(layout);
You'll need to maintain a reference to the layout (via a variable) so you can switch between panels.
Now that we have a "deck" panel, we need to add some cards. We do this by creating more JPanels, and specifying a name when we add it to the frame (constraints):
JPanel firstCard = new JPanel();
JPanel secondCard = new JPanel();
deck.add(firstCard, "first");
deck.add(secondCard, "second");
The first card added to the deck will always be the first one to show.
Once you have all your cards added, you can switch between them by calling layout.show(deck, "second");. This is how you use CardLayout to manage multiple panels within your container.
Creating listeners
There's no easier way to manage it. It only gets harder from there (bindings - I highly suggest you look into them). For listeners, there are 2 steps:
Create the listener
Add it to the component
Could be 1 if you created the listener "on the fly" using a lambda:
JButton button = new JButton();
//Java 8+
button.addActionListener(event -> {
//whenever you click the button, code in here triggers
});
For those who don't use Java 8, you will need to use an anonymous class:
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
//whenever you click the button, code in here triggers
}
});
Only some components support ActionListener. Anything that extends AbstractButton, like JMenuItem, JButton, JRadioButton, and more will support ActionListeners. JTextField also supports it, even though it's not an AbstractButton. Every component supports KeyListener, though, which can also be used to listen for input events from the user.
If you have any questions about this, let me know and I'll be glad to answer them.
Using Swing Components
JFrame
You initialize a JFrame:
JFrame frame = new JFrame();
You then want to set the defaultCloseOperation, to determine what happens when the window closes:
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
There are different options, but EXIT_ON_CLOSE will terminate your program after closing the window. If you do not set the defaultCloseOperation, then your window will close, but your program will still be running. BIG NO NO. If you don't want the entire program to exit when you close the frame, use DISPOSE_ON_CLOSE.
After you have the close operation, you might be tempted to set the size. This is bad practice. Your frame should size depending on what's inside of it. To do this, you add your components to your frame, then call pack():
JButton button = new JButton("Button");
frame.add(button);
//add other components
frame.pack();
This will ensure your frame sizes to fit what's inside of it. You should always design GUI from the inside out, to ensure you always have enough room for what you need.
Containers
JFrame is a Container. Containers are just components that hold other components. All containers should have a LayoutManager to manage how components are laid out and, if needed, sized. JFrame isn't the only container though. JPanel is actually a container that's meant to be added to another container (or window). You can add things to a JPanel, then add that panel to another container. This is how you keep things neatly organized. Containers are pretty straight forward, so there's not much to talk about.
Content Pane
When you create a JFrame, it comes along with something called the contentPane. It is a JPanel nested within the JFrame. When you do frame.add(button), you'll notice that add actually refers to the contentPane:
//in Container class
public Component add(Component comp) {
addImpl(comp, null, -1); //where it's added
return comp;
}
//In JFrame class (overriding)
protected void addImpl(Component comp, Object constraints, int index) {
if(isRootPaneCheckingEnabled()) {
getContentPane().add(comp, constraints, index); //adds to content pane instead
} else {
super.addImpl(comp, constraints, index); //if root panes were not supported, which they currently are
}
}
You too can grab the contentPane from the frame using
Container pane = frame.getContentPane();
The reason why the contentPane is in Container form is to ensure a strong API (if JPanels were no longer going to be used for this, we wouldn't need to worry about changing the method type of getContentPane). Although, since it IS a JPanel, you can cast it back to it's original form:
JPanel pane = (JPanel) frame.getContentPane();
Although it's usually not needed. Using it as a Container tends to work just fine.
Layouts
JFrame, by default, uses BorderLayout, but you can change this by calling the setLayout method of the container:
FlowLayout layout = new FlowLayout();
frame.setLayout(layout);
Before jumping into layouts, I want to mention that JPanels use FlowLayout as default, except for the frame's default contentPane, which you can also change by doing frame.setContentPane(...). The contentPane uses BorderLayout as default.
Now, lets talk about a couple, starting with the JFrame default: BorderLayout.
Some layouts require what are called constraints, which tell the layout how to handle that specific component that's being added. You specify these constraints when you add the component to the container:
frame.add(button, BorderLayout.SOUTH);
BorderLayout is pretty simple. You have 5 options: NORTH, SOUTH, EAST, WEST, or CENTER. (there are other values such as PAGE_START, which are interchangeable. It's best to just use the easier form)
All constraints for BorderLayout are static field variables that you call similar to how I did. BorderLayout is actually an easy layout to use, seeing how there's not much to it. Even though it's simplicity limits what you can do (you can only put it in a certain position like NORTH), you'd usually combine layouts to get the result you want. This layout can be very powerful when combined with other layouts.
FlowLayout is pretty straight forward, as well as other layouts out there. One of the less straight-forward ones would be GridBagLayout, which can be a really flexible layout. It can also be pretty complex, though, as the documentation even states.
When using GridBagLayout, you need to create a constraints object: GridBagConstraints. To work with GridBagLayout, you set the constraints using the constraints object, then add both the component and the constraints to the container:
frame.setLayout(new GridBagLayout());
GridBagConstraints gbc = new GridBagConstraints();
JButton button = new JButton("yoyoyo");
frame.add(button, gbc);
Even if we don't adjust the constraints, we MUST still specify it when adding a component to the container.
Lets say we had 4 buttons, and we wanted to put them side by side. You would adjust the constraint's gridx and gridy values:
JButton button = new JButton("1");
JButton button2 = new JButton("2");
JButton button3 = new JButton("3");
JButton button4 = new JButton("4");
frame.add(button, gbc);
gbc.gridx = 1; //or gridx += 1, or gridx = 1. gridx starts at 0
frame.add(button2, gbc);
gbc.gridx = 0; //must reset the value back to normal
gbc.gridy = 1;
frame.add(button3, gbc);
gbc.gridx = 1;
//since gridy already == 1, no need to change it
frame.add(button4, gbc);
We can use the same constraints object, as long as we reset values when needed.
GridBagLayout starts centered, and works from the center out, unless you specify otherwise. You cannot skip grid spaces either. Also, as you'll notice, all your buttons will be touching. If you wanted a little space between each component, you can set the insets of the constraints:
int top = 5, left = 5, bottom = 1, right = 1;
gbc.insets.set(top, left, bottom, right);
There is a LOT more to this layout, and sadly I just don't feel this is the best place to give the explanation to it all, seeing how it's already documented (I even added the link).
There are many other layouts out there. Get familiar with as many as you possibly can, then find the ones that'll help suit your needs. Positioning should ALWAYS rely on the LayoutManager that's being used. As for sizing, that kinda depends on the layout you're using.
I would highly recommend using JavaFX. It's a very nice fairly easy to use GUI system with nice looking and customizable controls. JavaFX events (basically ActionListeners) are pretty straightforward as well.
This should get you started: http://docs.oracle.com/javase/8/javafx/get-started-tutorial/get_start_apps.htm#JFXST804
I believe CardLayout is what you're looking for. With it, the programmer can choose which JPanels should be visible in the JFrame. Upon user interaction you can switch the contents of the JFrame without new JFrames or JOptionPanes popping up.
Is there an easier way than using Swing for simple games? Swing has a learning curve, but with the right resources and practice you can learn to build simple GUI applications pretty quickly.
I am new to Java swing coding. I am trying to copy JPanel contents to a new JPanel which uses contents of original JPanel to show. Also, the original JPanel contents are changing as records are changing. I tried the following code but it's totally useless.
public void addPanel(JPanel jp)
{
JPanel jp1=new JPanel();
int count=jp.getComponentCount()-1;
for(;i>=0;i--)
{
jp1.addComponent(jp.getComponent(i);
}
//after this I am setting bounds of jp1.
this.add(jp1);
}
This doesn't work if I want to make multiple JPanels as original JPanel changes. It overwrites the contents of new 'jp' over 'jp1' if used multiple times, say if used in a for loop.
I do not want to remove components of original JPanel. How can I do that?
Moving instances of Component is possible but coping them requires you to do it manually.
You can do this as a program by creating new instances of the origin class and then calling the setters with the values of the getters... But frankly, thats an error prone way and you'll need reflection for it which you shouldn't use unless really necessary.
What you can do is to override the standard Java Classes you use (e.G. JLabel) and in your overridden class you implement Cloneable where you set the parameters you need (text, bounds, whatever) then call your function like this:
public void addPanel(JPanel jp)
{
JPanel jp1=new JPanel();
int i=jp.getComponentCount()-1;
for(;i>=0;i--)
{
jp1.addComponent(
((Component) // this casts the clone back to component. This is maybe superfluous.
((Cloneable)jp.getComponent(i) // You have to ensure that all components that are returned are in fact instances of Cloneable.
).clone()
));
}
//after this I am setting bounds of jp1.
this.add(jp1);
}
If you go down that road, be sure to read the Documentation of Cloneable.
Here is method for solving the following problem without coding just using design views of JPanels/JFrames.
You can go to Navigator in design view select all JPanel components and copy them by typing ctrl+a and ctrl+c.
Then create another one JPanel and in design view, just paste them with ctrl+v.
Result: You get all components same size, dimensions and positions with same properties and values. After you do this, you can easily change whatever you want by using properties of GUI forms.
One of my classes is returning a JPanel which is added on a JFrame by some other class.
The JPanel contains a JTree and some buttons. On some events the panel is created again and returned to the JFrame.
My problem is that I have to add the JPanel to the Container of the JFrame again and then resize the frame for changes to be visible. I can't figure how to have the frame update without resizing.I tried removing old objects and adding updated ones but still doesn't work.
What is the best way to deal with this issue? Ideally I would have a reference to the JPanel and when the JPanel is changed, the frame will also be updated.
The whole model is changing not just its data. I will probably change this in the future but for now when data change a new JTree is created
Then your code should be something like:
JTree tree = new JTree( theNewModel );
scrollPane.setViewportView( tree );
That is you need to add the new JTree to the GUI, you can't just change the reference to the tree variable.
Or even easier, you don't need to create a new JTree, just replace the model in the existing tree using:
tree.setModel( theNewModel );
If this still doesn't help then you need to post your SSCCE that demonstrates the problem because your question still isn't clear.
try JFrame.invalidate() first, then call JFrame.validate()
http://docs.oracle.com/javase/6/docs/api/java/awt/Container.html#invalidate%28%29
My question boils down to this: is it standard structure in Swing programming to give listeners control over new components (e.g a new JPanel) for display and input, and to give that new component's listeners control over new components for display and input, and so on to infinity? Or does Java need to revert back to some sort of unifying class that ties all Swing components together in a procedural order?
At present, in my application that uses one JFrame only, in my listeners, my initial JFrame object is being passed as a parameter to all my JPanels so their listeners can call removeall() to clear the frame for a new JPanel. For example, short code as follows
public class MainFrame {
JFrame jfrm;
public MainFrame() {
jfrm = new JFrame("Main Frame");
JPanel mainPanel = new MainPanel(jfrm);
}
}
public class MainPanel extends JPanel {
public MainPanel(final JFrame mainFrame) {
JButton example = new JButton("Example");
example.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent le) {
mainFrame.removeall();
JPanel 2ndPanel = new 2ndPanel(mainFrame);
mainFrame.add(2ndPanel);
mainFrame.validate();
}
});
}
}
Is this the right structure - where it's the listeners that generate the new panels and not some unifying class? But if that's the case, how does Java's compiler ever get to mainFrame.validate() if there's a cascading infinity of listeners? I'm an old-school procedural programmer trying to program a Swing application in Java, and I reckon I might not have grasped the basic concepts of Swing programming. Look forward to any helpful answers, and thanks in advance!
I wouldn't do it like that. The Observer pattern is used in Swing to send notifications, usually as a result of an user action.
Take your example: The user 'clicks' on the button because he wants a new panel in MainFrame. But the button doesn't know what to do with a click. All he can do is notify event listeners, that it has been selected.
So we need some component that is interested in notifications. This component can register a listener with the button and receive notifications. The listener is this other components 'ear' (or it's 'eye'). But an ear (or eye) will not take action. It is just the other components sensor.
Which takes us back to the main question: who wants to be informed, if the button is clicked and who has to take action. This is a major design question. It's definitly not the listener that creates and adds a panel to main frame. It could be the main frames role to create and add sub panels or the role of a third component, which is responsible of creating a frame with sub panels.
But the listner is a bad place for this code.
Instead of destroying and creating panels you might want to look at hiding/showing them. There is a CardLayout layout manager that can do this: http://journals.ecs.soton.ac.uk/java/tutorial/ui/layout/card.html
Basically the idea is build and add all your panels at the start of your prog, then use the layout manager to flip between views.
As said by others, you might want to add some sort of model to your design, which is responsible for maintaining the state of the system.
First of all you shouldn't let the listener manipulate the frame directly, use a nested JPanel or it's ContentPane.
Your question depends on where your listener is located. You should only add components to a JFrame from the class itself. In your case it's OK, since the logic is confined to the class itself.
I don't think there is an infinity of listeners. They are in a list and are executed sequentially. Your listener should use SwingUtilities.invokeLater for manipulating the main frame.
I find the passing of the JFrame as an argument a little redundant. Why not create the listener from outside the constructor?
final JPanel mainPanel = new MainPanel();
JButton example = new JButton("Example");
example.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent le) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
MainFrame.this.removeAll();
MainFrame.this.add(mainPanel);
}
});;
}
});
add(example);
It's not the best of examples, but I am note sure what you are trying to do.
The bottom line is you should create the components outside the listener, and then add it using the listener.
There is some confusion by the, not unusual, way you have organised your code. As a general rule of Java, don't subclass where you have no reason to. It rarely makes sense to subclass JPanel or JFrame.
It also rarely makes sense to assign components to fields in the class that creates them. In fact, do less in constructors.
Also do less in anonymous inner classes. Detangle the event data and call a method that makes sense for the enclosing class to have as an operation.
I want to know how I can make a Java program where an unknown amount of objects can be added to a GUI depending on user input. I can program in objects one at a time within the program, but I haven't seen a more dynamic program.
Can I do that with Java? If not, what can I do it with?
For more information, here's a picture.
There can be more than one question per question block, and each question can have it's own question block.
Yes you can dynamically add and remove components. The basic code would be:
panel.add( ... );
panel.revalidate();
panel.repaint();
Ofcourse you can do it with Java Swings. All you gotta do is based on user input you gotta take a decision to add new JPanels. From the picture you've given in the example, you would need to add a Q&A block dynamically. Simply attach that to any event handler within your application so that it gets added dynamically
public getQandAPanel(){
JPanel questPanel = new JPanel();
JPanel answerPanel = new JPanel();
JPanel wrappingPanel = new JPanel();
wrappingPanel.setLayout(new GridLayout(0,1));
//CODE TO DECORATE question and answer panels should go here
wrappingPanel.add(questPanel);
wrappingPanel.add(answerPanel);
}
Now everytime when you call this getQandAPanel, this would return you a fresh JPanel everytime which you can add it to your parent JFrame. You should have a good idea of Java Swings to know what I'm talking about.