Develop Reference

How to avoid Hgap for first component added to a JPanel using FlowLayout

In my software i have a JPanel containing some JComponent. The JPanel use a FlowLayout with a certain Hgap to separate these components.
I'm trying to have this kind of design, but the first component should be layed out on left, without any Hgap. Like This:
here is the code you can use to generate the example:
public class FlowLayoutExample {
public static void main(String [] a) {
final JFrame frame = new JFrame();
frame.setSize(new Dimension(500, 80));
frame.setMinimumSize(new Dimension(350, 80));
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setContentPane(initJPanel());
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
frame.setVisible(true);
}
});
}
private static JPanel initJPanel() {
JPanel panel = new JPanel();
FlowLayout flowLayout = new FlowLayout(FlowLayout.LEFT);
flowLayout.setHgap(25);
panel.setLayout(flowLayout);
panel.setBackground(Color.LIGHT_GRAY);
panel.add(initLabel());
panel.add(initLabel());
panel.add(initLabel());
panel.add(initLabel());
return panel;
}
private static Component initLabel() {
return new JLabel("MyLabel");
}
}
Thanks for any suggestion you'll leave !

You can use an EmptyBorder to fake it out:
panel.setBorder( new EmptyBorder(0, -25, 0, 0) );
Basically the border inset and layout gap are added together.

Why not jframe shows button?

public class Benim extends JFrame {
Container contentArea = getContentPane ();
public Benim(){
JFrame frame=new JFrame("Concentration");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
setSize(800, 800);
JButton start=new JButton("Start");
JPanel pane=new JPanel();
pane.add(start);
setVisible(true);
frame.add(start);
frame.add(pane);
/* setContentPane(Container)
JRootPane createRootPane()*/
}
public static void main (String []args){
new Benim();
}
}
My code is that. I tried adding to panel first then adding panel to frame, adding to frame directly. Adding a rootpane but still my button doesnot appear. I am trying to learn for 2 days but i am still at same point.

The instance of JFrame that is shown does not have the JButton added.
Instead invoke setVisible on the JFrame directly
You almost never want to extend JFrame as no new functionality is added
Other points to note
Call setVisible after components have been added
setSize is unnecessary - let pack determine container size
This is the result
public class Benim extends JFrame {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
JFrame frame = new JFrame("Concentration");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JButton start = new JButton("Start");
JPanel pane = new JPanel();
pane.add(start);
pane.add(start);
frame.add(pane);
frame.pack();
frame.setVisible(true);
}
});
}
}

Why another instance of JFrame? You are extending it, so just call super().
public class Benim extends JFrame {
Container contentArea = getContentPane ();
public Benim(){
super("Concentration");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
pack();
setSize(800, 800);
JButton start=new JButton("Start");
JPanel pane=new JPanel();
pane.add(start);
add(pane);
setVisible(true);
}
public static void main (String []args){
new Benim();
}
}
Reimeus also rightfully points out that you don't need to extend JFrame if you don't plan on extending functionality. See his example for an alternative implementation.

JButton Layout set

In my code, My okButton is in bad appear, so large and long, How fix this problem?
public class d7Table extends JFrame {
public JTable table;
public JButton okButton;
public d7Table() {
table = new JTable(myTableModel(res));
okButton = new JButton("Ok");
add(new JScrollPane(table), BorderLayout.CENTER);
add(okButton, BorderLayout.PAGE_END);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setSize(800, 600);
this.setLocation(300, 60);
this.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new d7Table();
}
});
}
}
I remove Irrelevant codes.

You've added the button to the SOUTH position of a BorderLayout. This is the default behaviour of BorderLayout.
To fix it, create another JPanel, add your button to it, then add the panel to the SOUTH position instead
Take a look at
A visual guide to layouts
Using Layout Managers
The approach mentioned above is commonly known as compound layouts, as you use a series of containers with different layout managers to achieve the desired effect.
JPanel buttonPane = new JPanel(); // FlowLayout by default
JButton okayButton = new JButton("Ok");
buttonPanel.add(okayButton);
add(okayButton, BorderLayout.SOUTH);

Because the default layout of JFrame is BorderLayout, and PAGE_END means the bottom of the frame horizontally like this:
You have to change the layout of the frame, but don't do that, just create a panel, and add the components to it then add the panel to the container.
JPanel p = new JPanel();
p.add(okButton);
add(p,BorderLayout.PAGE_END);
Here some links may help you understand more about layout managers that usually used:
How To Use BorderLayout
How To Use FlowLayout
And MigLayout which I prefer to use it as it's very flexible layout manager, try it it's amazing.

import java.awt.*;
import javax.swing.*;
public class TableAndButton extends JFrame {
public JTable table;
public JButton okButton;
public TableAndButton() {
table = new JTable();
okButton = new JButton("Ok");
add(new JScrollPane(table), BorderLayout.CENTER);
JPanel bottomPanel = new JPanel();
bottomPanel.add(okButton);
add(bottomPanel, BorderLayout.PAGE_END);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//this.setSize(800, 600); better to call pack()
this.pack();
//this.setLocation(300, 60); better to..
this.setLocationByPlatform(true);
this.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new TableAndButton();
}
});
}
}

location and size of jtextarea in jscrollpane is not set

I am working on the editor. I am using Java swing for it. I have embedded a JTextArea with JScrollPane. i want to position the jtextarea of particular size at the middle of JScrollPane. To do this I used setLocation function. But this is not working?
public class ScrollPaneTest extends JFrame {
private Container myCP;
private JTextArea resultsTA;
private JScrollPane scrollPane;
private JPanel jpanel;
public ScrollPaneTest() {
resultsTA = new JTextArea(50,50);
resultsTA.setLocation(100,100);
jpanel=new JPanel(new BorderLayout());
jpanel.add(resultsTA,BorderLayout.CENTER);
scrollPane = new JScrollPane(jpanel,JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
scrollPane.setPreferredSize(new Dimension(800, 800));
scrollPane.setBounds(0, 0, 800, 800);
setSize(800, 800);
setLocation(0, 0);
myCP = this.getContentPane();
myCP.setLayout(new BorderLayout());
myCP.add(scrollPane);
setVisible(true);
addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
}
public static void main(String[] args) {
new ScrollPaneTest();
}
}

You simply have to add the JTextArea to the JScrollPane, and add it to the CENTER of the JPanel having BorderLayout.
Don't use AbsolutePositioning. Add a proper LayoutManager, and let LayoutManager do the rest for positioning and sizing your components on the screen.
In order to use the setBounds(...) method you have to use a null Layout for your component, which is not worth using, provided the perspective, as mentioned in the first paragraph of the AbsolutePositioning. Though in the code example provided by you, you are doing both the thingies together i.e. using Layout and using AbsolutePositioning, which is wrong in every way. My advice STOP DOING IT :-)
In the example provided the ROWS and COLUMNS provided by you are sufficient to size the JTextArea by the Layout concern.
Code Example :
import java.awt.*;
import javax.swing.*;
public class Example
{
private JTextArea tarea;
private void displayGUI()
{
JFrame frame = new JFrame("JScrollPane Example");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
JPanel contentPane = new JPanel();
contentPane.setLayout(new BorderLayout(5, 5));
JScrollPane textScroller = new JScrollPane();
tarea = new JTextArea(30, 30);
textScroller.setViewportView(tarea);
contentPane.add(textScroller);
frame.setContentPane(contentPane);
frame.pack();
frame.setLocationByPlatform(true);
frame.setVisible(true);
}
public static void main(String... args)
{
EventQueue.invokeLater(new Runnable()
{
#Override
public void run()
{
new Example().displayGUI();
}
});
}
}

Centering Panel in Java

For some reason i am having problems centering my panel vertically that is located inside another panel. I do exactly as the examples i studied but still no luck.
Down there is my code. Despite using setAlignmentY(0.5f) on my container panel, it still wont center when i resize the window.
Also the components inside container panel wont center either, despite setAligenmentX(0.5f).
I wonder if there is a solution for this, I pretty much tried everything out there but couldnt find a solution.
JLabel idLabel;
JLabel passLabel;
JTextField id;
JTextField pass;
JButton enter;
JPanel container;
public JournalLogin()
{
//setLayout(new FlowLayout());
//setPreferredSize(new Dimension(500, 500));
//setBorder(BorderFactory.createEmptyBorder(100, 100, 100, 100));
container = new JPanel();
container.setLayout(new MigLayout());
container.setAlignmentX(0.5f);
container.setAlignmentY(0.5f);
container.setPreferredSize(new Dimension(300, 300));
container.setBorder(BorderFactory.createTitledBorder("Login"));
add(container);
idLabel = new JLabel("ID:");
idLabel.setAlignmentX(0.5f);
container.add(idLabel);
id = new JTextField();
id.setText("id");
id.setAlignmentX(0.5f);
id.setPreferredSize(new Dimension(80, 20));
container.add(id, "wrap");

setAlignmentX and Y are not the way to go about doing this. One way to center a component in a container is to have the container use GridBagLayout and to add the component without using any GridBagConstraints, a so-called default addition. There are other ways as well.
For example to alter Nick Rippe's example (1+ to him):
import java.awt.BorderLayout;
import java.awt.Dimension;
import java.awt.GridBagLayout;
import javax.swing.*;
public class UpdatePane2 extends JPanel {
private static final int PREF_W = 300;
private static final int PREF_H = 200;
public UpdatePane2() {
JPanel innerPanel = new JPanel();
innerPanel.setLayout(new BorderLayout());
innerPanel.add(new JLabel("Hi Mom", SwingConstants.CENTER),
BorderLayout.NORTH);
innerPanel.add(new JButton("Click Me"), BorderLayout.CENTER);
setLayout(new GridBagLayout());
add(innerPanel);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(PREF_W, PREF_H);
}
private static void createAndShowGui() {
JFrame frame = new JFrame("UpdatePane2");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new UpdatePane2());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}

Alignments tend to be pretty picky in Swing - they do [usually] work... but if all you're looking for is a panel that's centered, I'd recommend using Boxes in the BoxLayout (My personal favorite LayoutManager). Here's an example to get you started:
import java.awt.Dimension;
import javax.swing.*;
public class UpdatePane extends JPanel{
public static void main(String... args) {
SwingUtilities.invokeLater(new Runnable(){
#Override
public void run() {
//Create Buffers
Box verticalBuffer = Box.createVerticalBox();
Box horizontalBuffer = Box.createHorizontalBox();
verticalBuffer.add(Box.createVerticalGlue()); //Top vertical buffer
verticalBuffer.add(horizontalBuffer);
horizontalBuffer.add(Box.createHorizontalGlue()); //Left horizontal buffer
//Add all your content here
Box mainContent = Box.createVerticalBox();
mainContent.add(new JLabel("Hi Mom!"));
mainContent.add(new JButton("Click me"));
horizontalBuffer.add(mainContent);
horizontalBuffer.add(Box.createHorizontalGlue()); //Right horizontal buffer
verticalBuffer.add(Box.createVerticalGlue()); //Bottom vertical buffer
// Other stuff for making the GUI
verticalBuffer.setPreferredSize(new Dimension(300,200));
JFrame frame = new JFrame();
frame.add(verticalBuffer);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.pack();
frame.setVisible(true);
}
});
}
}

You will need to get the LayoutManager to center the layout for you. Currently it looks like the implementation of "MigLayout" does not honor the Alignment. Try changing it or creating a subclass.