I am new to Java and am trying to run this code. What could be error in the following code—my JTextField, txtfld, is shown just as a line instead of as a full text box?
public class calculator
{
public static void main(String s[])
{
JFrame j=new JFrame();
j.setSize(400,600);
JPanel p1=new JPanel();
JPanel p2=new JPanel();
p1.setSize(400, 100);
p2.setSize(400, 500);
p1.setLocation(0, 0);
p2.setLocation(0, 100);
p2.setLayout(new GridLayout(4,4));
j.add(p1);
j.add(p2);
JTextField txtfld=new JTextField();
txtfld.setSize(390, 92);
txtfld.setLocation(5, 2);
//txtfld.setVisible(true);
p1.add(txtfld);
j.setVisible(true);
}
}
JTextField txtfld=new JTextField();
You need to give a hint to the layout manager what the size should be.
So you should use something like:
JTextField txtfld=new JTextField(10);
Now the preferred size will be such that 10 "W" characters can be displayed in the text field before scrolling is required.
You should also pack() the frame before making it visible:
j.pack();
j.setVisible();
This will allow the frame to display all the components at their preferred sizes.
Also, get rid of all the setSize() and setLocation() statements. It is the job of the layout manager to set the size and location. Those values will be recalculated by the layout manager.
j.add(p1);
j.add(p2);
The default layout manager for a frame is a BorderLayout. So the above code will cause p2 to replace p1 on the frame.
Basically your entire code is wrong.
Start by reading the section from the Swing tutorial on How to Use Layout Managers for more information and working examples to get you started. Maybe start with the BorderLayout example, since this is the default layout of the frame you need to understand how it works first.
Related
I am trying to use Java Swing to create a simple GUI in which I have a drawing pad and some buttons it all works fine until I add this code for the JTextField:
String text = "hello";
JTextArea textArea = new JTextArea(text);
textArea.setPreferredSize(new Dimension(500, 50));
textArea.setEditable(false);
Before adding this code the drawpad displays on the left of the screen followed by the buttons, when I add this only the drawpad is displayed unless I resize the frame in which case the buttons and text field reappear although the text field is hidden behind the drawpad slightly. Here is the full code:
public class testGUI extends Frame{
public static void main(String[] args) {
JFrame frame = new JFrame("Neural Networks");
frame.setSize(700, 300); //set the size of the frame
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true); //make it visible
Container content = frame.getContentPane();
content.setLayout(new BorderLayout());
JPanel mainPanel = new JPanel();
final PadDraw drawPad = new PadDraw();
drawPad.setSize(100, 100);
content.add(drawPad);
JButton clearButton = new JButton("Clear");
clearButton.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
drawPad.clear();
}
});
JButton loadButton = new JButton("Load");
loadButton.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
//Load something here
}
});
JButton testButton = new JButton("Test Draw Pad Image");
testButton.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
//
}
});
JButton loadImage = new JButton("Test image from file");
loadImage.addActionListener(new ActionListener(){
public void actionPerformed(ActionEvent e){
//String filename = textField.getText();
}
});
String text = "hello";
JTextArea textArea = new JTextArea(text);
textArea.setPreferredSize(new Dimension(500, 50));
textArea.setEditable(false);
mainPanel.add(clearButton);
mainPanel.add(loadButton);
mainPanel.add(testButton);
mainPanel.add(loadImage);
mainPanel.add(textArea);
content.add(mainPanel);
}
}
You're adding the drawPad and the mainPanel to the content panel, which uses BorderLayout, without specifying any location. They thus end up both in the center position of the border layout, which is supposed to contain only one component.
See How to use BorderLayout in the Swing tutorial.
Also note that setting the preferred size is not something you should do. Instead, the preferred size is supposed to be automatically computed based on other sttings (the contained components, the number of rows and columns of a text area, etc.)
And a JTextArea should be enclosed into a JScrollPane to be good-looking and allow you to scroll.
JPanel mainPanel = new JPanel();
The default layout for a JPanel is a FlowLayout, so all the components flow on a single row. If there is not enough room on the row then the components wrap to the next row.
So when you add the JTextArea the flow is disturbed. The solution is to use a combination of layout managers to get your desired layout effect. Read the section from the Swing tutorial on Using Layout Managers for more information and examples.
JTextArea textArea = new JTextArea(text);
textArea.setPreferredSize(new Dimension(500, 50));
Also, you should NOT set the preferred size of the text area (or any Swing component for that matter). Instead you should do something like:
JTextArea textArea = new JTextArea(rows, columns);
and let the component determine its own preferred size. Also a text area is typically used with a JScrollPane and then you add the scroll pane to your panel:
JScrollPane scrollPane = new JScrollPane( textArea );
Edit:
Taking a second look at your code you have many more problems.
The point of using a layout manager is to have the layout manager set the size and location of the components. So your code should not have any logic related to the size/location of a component.
When you use the add(...) statement on a BorderLayout without a constraint, the component gets added to the CENTER. However only the last component added is managed by the BorderLayout. So only the "mainPanel" is given a size/location by the layout manager. That is why you need the setSize(...) statement on the drawPad to make the component visible. Although you now have the problem that two components are painted in the same space.
So to see the drawPad on the left you might want to use:
content.add(drawPad.BorderLayout.LINE_START);
However this still probably won't work because I'm guessing you are doing custom painting on the draw pad which means you will also need to override the getPreferredSize() method of the class so the layout manager can use the information to determine the size of the component. Read the section from the Swing tutorial on Custom Painting for more information and working examples.
Finally some other issues:.
The setVisible(...) statement should be invoked AFTER all the components have been added to the frame.
To follow Java standards, class names should start with an upper case character.
You should NOT be extending "Frame". There is no need to extend any class in your example.
Read the tutorial and download the demos for examples of better structured code.
So I'm writing a program in which I wish to have a single JFrame containing a JPanel header in a separate colour and directly underneath have a grid of buttons in a separate JPanel. So far my program works perfectly except for the fact that the header String isn't showing up in the NORTH panel. Instead I'm getting a box containing the set background colour with a small grey box in the centre. I'm wondering if I didn't set the size of the panel correctly?
I have heard this can be accomplished using JLabel, but when I tried to do this, it would not show the background colour that I had set.
So, could anyone please show me how to achieve the following either with the JPanel (preferably because I would like to know how it works and what I'm missing) or with JLabel: filling that little grey box in the middle of the header with a String.
Here is my code:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Example {
public static void main(String[] args) {
// Initialize a panel for the header, and mainGrid which will contain buttons
JPanel panel = new JPanel();
JPanel header = new JPanel();
JPanel mainGrid = new JPanel();
// Initialize the header
DisplayPanel message = new DisplayPanel();
header.setBackground(Color.ORANGE);
header.add(message);
// Initialize the mainGrid panel
mainGrid.setLayout(new GridLayout(2,2,2,2));
mainGrid.add(new JButton("1"));
mainGrid.add(new JButton("2"));
mainGrid.add(new JButton("3"));
mainGrid.add(new JButton("4"));
// Add the two subpanels to the main panel
panel.setLayout(new BorderLayout());
panel.add(header, BorderLayout.NORTH); // The issue is this panel isn't displaying the String created in DisplayPanel
panel.add(mainGrid, BorderLayout.CENTER);
// Add main panel to JFrame
JFrame display = new JFrame("Test");
display.setContentPane(panel);
display.setSize(200,100);
display.setLocation(500,200);
display.setVisible(true);
display.setResizable(false);
display.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
private static class DisplayPanel extends JPanel {
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.drawString("header" , 20, 20); // The string I want to be displayed
}
}
}
I would very much appreciate anyone's help or input as I have only been studying Java for a few months and this is my first post. Thank you in advance.
Also, any general tips on writing that you may have would be greatly appreciated.
I'm wondering if your problem is that you're nesting your message JPanel inside of the header JPanel, and the container header JPanel uses the JPanel default FlowLayout. Thus the component it holds won't expand on its own and will remain trivially small.
Consider either giving the header JPanel a BorderLayout so that message expands inside of it, or
use a JLabel to show your text, not a JPanel's paintComponent method. The JLabel should size itself to be big enough to show its text. If you do this and want it to show a background color, all you have to do is call setOpaque(true) on your JLabel, and you're set.
Actually, if you nest the JLabel, then there's no need to make it opaque. Just do this:
JPanel header = new JPanel();
JPanel mainGrid = new JPanel();
JLabel message = new JLabel("Header", SwingConstants.CENTER);
header.setBackground(Color.ORANGE);
header.setLayout(new BorderLayout());
header.add(message);
I would highly recommend using a GUI builder WYSIWYG IDE, like NetBeans, where you can easily drag and drop components to where they need to be. If you're doing any sort of complex GUI layout, it can be madness (and in my opinion, nonsensical) trying to write and maintain the code.
The layout your trying to implement would be trivial in NetBeans.
I'm trying to set the size of JTextField, but for some reason it stays the same size and fills up the whole JPanel, I am using setPreferredSize, but this makes no difference:
JPanel loginJPanel = new JPanel(new BorderLayout());
JTextField usernameJTextField = new JTextField();
usernameJTextField.setPreferredSize(new Dimension(50, 100));
loginJPanel.add(usernameJTextField);
It does make a difference, but the layout may choose to ignore preferred size settings. The center area of BorderLayout gets as much of the available space as possible. See How to Use BorderLayout for more details.
Consider this example that packs the frame, as a result the preferred size of the text field is respected. But once the frame is resized, the text field is resized as well.
import javax.swing.*;
import java.awt.*;
class Demo {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
JPanel loginJPanel = new JPanel(new BorderLayout());
JTextField usernameJTextField = new JTextField();
usernameJTextField.setPreferredSize(new Dimension(50, 100));
loginJPanel.add(usernameJTextField);
JFrame frame = new JFrame();
frame.add(loginJPanel);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
});
}
}
Take a look at Visual Guide to Layout Managers and perhaps you would find a more suitable layout for your needs.
Also, see Should I avoid the use of set(Preferred|Maximum|Minimum)Size methods in Java Swing?.
EDIT:
Note that you're usually encouraged to specify the number of columns when initializing text fields. This number is used to calculate preferred width. For example textField = new JTextField(20); See How to Use Text Fields for more details:
If you do not specify the number of columns or a preferred size, then
the field's preferred size changes whenever the text changes, which
can result in unwanted layout updates.
Since you set layout manager of your jpanel to BorderLayout, it adds jtextfield to center by default. Use a null layout instead.
JPanel loginJPanel = new JPanel(null);
I'm using the seaglass look and feel in my application. How do I set the height for a JButton?
It seems like there is no way to have a custom height. I took a look at the documentation:
http://seaglass.googlecode.com/svn/doc/client-properties.html
and I tought I had to use JComponent.sizeVariant = scale to solve the problem, but it doesn't work.
How can I solve this?
Thanks trashgod, I tried this:
try {
UIManager.setLookAndFeel("com.seaglasslookandfeel.SeaGlassLookAndFeel");
} catch(Exception e) {
e.printStackTrace();
}
JButton button = new JButton("Test");
button.putClientProperty("JComponent.sizeVariant", "scale");
JPanel panel = new JPanel(new BorderLayout());
panel.add(button);
panel.setPreferredSize(new Dimension(500, 400));
JFrame frame = new JFrame();
frame.setContentPane(panel);
frame.pack();
frame.setVisible(true);
but doesn't seem to work either. Thanks anyway for your effort.
As shown here, here and here, the JComponent.sizeVariant property value is a String, e.g. "mini", "small", "regular" and "large". For "scale" to work, the enclosing panel's layout must allow the component to resize. In the variation below, GridLayout is used:
f.add(variantPanel("scale"));
…
private static JPanel variantPanel(String size) {
JPanel variantPanel = new JPanel(new GridLayout());
…
return variantPanel;
}
Your frame contains one panel. When you pack the frame the panel will be sized at 500x400, i.e., its preferred size. Your panel uses a BorderLayout. BorderLayout does not use the button preferred size. It will expand the button to fill the entire panel size. Try using a layout for your panel that respects the preferred size of its components, e.g., FlowLayout. If you want to change the button size you can then set the button's preferred size.
I have a JPanel subclass on which I add buttons, labels, tables, etc. To show on screen it I use JFrame:
MainPanel mainPanel = new MainPanel(); //JPanel subclass
JFrame mainFrame = new JFrame();
mainFrame.setTitle("main window title");
mainFrame.getContentPane().add(mainPanel);
mainFrame.setLocation(100, 100);
mainFrame.pack();
mainFrame.setVisible(true);
mainFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
But when I size the window, size of panel don't change. How to make size of panel to be the same as the size of window even if it was resized?
You can set a layout manager like BorderLayout and then define more specifically, where your panel should go:
MainPanel mainPanel = new MainPanel();
JFrame mainFrame = new JFrame();
mainFrame.setLayout(new BorderLayout());
mainFrame.add(mainPanel, BorderLayout.CENTER);
mainFrame.pack();
mainFrame.setVisible(true);
This puts the panel into the center area of the frame and lets it grow automatically when resizing the frame.
You need to set a layout manager for the JFrame to use - This deals with how components are positioned. A useful one is the BorderLayout manager.
Simply adding the following line of code should fix your problems:
mainFrame.setLayout(new BorderLayout());
(Do this before adding components to the JFrame)
If the BorderLayout option provided by our friends doesnot work, try adding ComponentListerner to the JFrame and implement the componentResized(event) method. When the JFrame object will be resized, this method will be called. So if you write the the code to set the size of the JPanel in this method, you will achieve the intended result.
Ya, I know this 'solution' is not good but use it as a safety net.
;)
From my experience, I used GridLayout.
thePanel.setLayout(new GridLayout(a,b,c,d));
a = row number, b = column number, c = horizontal gap, d = vertical gap.
For example, if I want to create panel with:
unlimited row (set a = 0)
1 column (set b = 1)
vertical gap= 3 (set d = 3)
The code is below:
thePanel.setLayout(new GridLayout(0,1,0,3));
This method is useful when you want to add JScrollPane to your JPanel. Size of the JPanel inside JScrollPane will automatically changes when you add some components on it, so the JScrollPane will automatically reset the scroll bar.
As other posters have said, you need to change the LayoutManager being used. I always preferred using a GridLayout so your code would become:
MainPanel mainPanel = new MainPanel();
JFrame mainFrame = new JFrame();
mainFrame.setLayout(new GridLayout());
mainFrame.pack();
mainFrame.setVisible(true);
GridLayout seems more conceptually correct to me when you want your panel to take up the entire screen.