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Make a JLabel text vertically aligned to the center

How do I make a JLabel text vertically and horizontally aligned to the center?
I have to make use of setHorizontalTextPosition and setVerticalTextPosition. Can this be achieved by using these 2?
I have tried but the text remains at the top itself.
import java.awt.FlowLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingConstants;
public class label extends JFrame
{
private JLabel label;
public label() //constructor
{
super("Simple GUI");
setLayout(new FlowLayout());
label=new JLabel("Centered JLabel");
label.setHorizontalTextPosition(SwingConstants.CENTER);
label.setVerticalTextPosition(SwingConstants.CENTER);
add(label);
}
}

I have tried but the text remains at the top itself.
You have two problems:
Andrew addressed the first problem. You are using the wrong method.
Next you are using the wrong layout. The FlowLayout only display components on a single line so the component will always be at the top. Don't change the layout manager. The default layout manager for a JFrame is the BorderLayout. When you add a component to the CENTER (which is the default when you don't specify a constraint), the component will be sized to fill the entire frame. Then the "alignment" properties will control the position of the text within the size allocated to the label.
Or a different option is to use a GridBagLayout. Then you don't need to play with alignment options of the component:
setLayout( new GridBagLayout() );
add(label, new GridBagConstraints());
Try both options as both may be effective in different situations.
Read the Swing tutorial on Layout Managers to better understand how each layout manager works.

I'm very sorry to don't know why the setHorizontalTextPosition method and the setVerticalTextPosition method doesn't work.
But, I'll let you know that there're several ways to sort the text in the label by inserting parameters an alignment with String when we create the label.
First of all, camickr's answer is the best answer, Because Swing was designed to be used with layout managers!!
Please remember that the most recommended method is to apply GridBagLayout() to the Layout of JFrame by camickr.
This answer is intended to inform you that
This method is also possible, but not recommended in the normal case
Using this method is not recommended because changing the size of the frame
keeps the components in place, but it could give you a little help
when it is indicated that the size and location of components in the
container are used in a way that can be used in special cases, such as
when they need to be fixed without external impact.
To get a better idea of the problem, I'll simply change the code that you uploaded to me so that it can be executed.
import java.awt.FlowLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingConstants;
import java.awt.Color;
public class StackOver extends JFrame
{
private JLabel label;
public StackOver() //constructor
{
super("Simple GUI");
setLayout(null);
setSize(500,300);
label=new JLabel("Centered JLabel", JLabel.CENTER);
/*
label.setHorizontalTextPosition(SwingConstants.CENTER);
label.setVerticalTextPosition(SwingConstants.CENTER);*/
add(label);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setVisible(true);
}
public static void main(String[] args) {
// TODO Auto-generated method stub
new StackOver();
}
}
Hmm, let's put some color in JLabel's background to find out more.
label.setOpaque(true); //Transparency Settings
label.setBackground(Color.pink); //Specify background color
//to use 'Color' class, We must import java.awt.Color;
the JFrame setting was set to FlowLayout()which makes the location and size of components were fixed, so we couldn't see it working!
So now we're going to go through the next two processes.
1) Changing JFrame's layout to null to use Absolute Layout ("not recommended, just a case")
2) Changing the size and location of the JLabel
after the progress we can see that the text alignment works!
1) Changing JFrame's Layout
the following link: Layout Manager shows that there are so many Layouts outside of FlowLayout.
Swing is designed to use the layout manager, so of course you should use one of the Layout above link.
But, to use an interesting way that fix the location and size of components absolutely We will switch to setLayout(null);!
2) Changing the size and location of the JLabel
We can directly change the size and position of JLabel with setBounds(int startX, int startY, int Width, int Height) method!
import java.awt.FlowLayout;
import java.awt.Rectangle;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingConstants;
import java.awt.Color;
public class StackOver extends JFrame
{
private JLabel label;
public StackOver() //constructor
{
super("Simple GUI");
setLayout(null);
setSize(500,300);
label=new JLabel("Centered JLabel", JLabel.CENTER);
// Since it also sets the size of the JLabel,
//let's use the constructor to set the alignment of the text inside the JLabel.
label.setOpaque(true); //Transparency Settings
label.setBackground(Color.pink); //Specify background color
//to use 'Color' class, We must import java.awt.Color;
Rectangle r = this.getBounds(); //to get Frame Size
label.setBounds(r.x+100, r.y+100, r.width-200, r.height-200);
/*
label.setHorizontalTextPosition(SwingConstants.CENTER);
label.setVerticalTextPosition(SwingConstants.CENTER);*/
add(label);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setVisible(true);
}
public static void main(String[] args) {
// TODO Auto-generated method stub
new StackOver();
}
}
Now we can see the text of JLabel in the middle as intended!
This method can directly fix the size and location of all components (ex buttons), but the location and size of the components are fixed even if the window size of the JFrame changes after the program runs.
so If you really want set components Absolutely by this way, you rather to set JFrame Resizable false by adding below code on JFrame's code
this.setResizable(false);
I hope the answer was helpful to you and have a peaceful day!

How does one stretch a JButton to the full height of a JPanel

To summarize my problem, I am developing an interface for an application in Java. I have run into a problem I haven't previously faced yet.
To create a sort of "navigation bar" i created a thin JPanel at the top of the JFrame. Then I wanted to add a JButton to it to represent the "home" button which leads to the starting content of the application. When I did that and made width as well as height of the Button equal to the height of the Panel, the Button had a little gap of approximately 3 pixels to the top of the Panel. I don't know why that is, there is no other element inside the Panel. I am not using any layout, however i have tried to fix that problem using a FlowLayout but nothing really changed.
Here is the full code for the interface, i marked the menu panel with red color for testing purpose only. How do I get rid of that small gap to the top?
package UserInterface;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Toolkit;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Interface {
private JFrame frame;
private JPanel menu;
private JPanel content;
public JButton home;
public Interface() {
Dimension dim = new Dimension(50, 50);
frame = new JFrame();
menu = new JPanel();
content = new JPanel();
frame.setSize(1600, 900);
menu.setSize(1600, 50);
content.setSize(1600, 850);
frame.setTitle("Tierland");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLocation(
(int)((Toolkit.getDefaultToolkit().getScreenSize().getWidth() / 2) - (frame.getWidth() / 2)),
(int)((Toolkit.getDefaultToolkit().getScreenSize().getHeight() / 2) - (frame.getHeight() / 2))
);
frame.setSize(1600, 900);
menu.setSize(1600, 50);
content.setSize(1600, 850);
menu.setBackground(Color.RED);
home = new JButton();
home.setPreferredSize(dim);
home.setMinimumSize(dim);
home.setMaximumSize(dim);
home.setSize(dim);
frame.add(menu);
frame.add(content);
frame.setVisible(true);
menu.setVisible(true);
content.setVisible(true);
}
}

I am not using any layout,
Yes you are. By default a JPanel uses a FlowLayout.
however i have tried to fix that problem using a FlowLayout but nothing really changed.
That is because the default FlowLayout uses a 5 pixel gap around any component added to the panel.
You should be using:
menu.setLayout( new FlowLayout(...) );
Read the FlowLayout API for the appropriate constructor that will allow you to use 0, for the horizontal and/or vertical gap.
frame.add(menu);
frame.add(content);
Also, by default, the content pane of the frame uses a BorderLayout, so you should be using:
frame.add(menu, BorderLayout.PAGE_START);
frame.add(content, BorderLayout.CENTER);
You should not be attempting to control the size of the button:
//home.setPreferredSize(dim);
//home.setMinimumSize(dim);
//home.setMaximumSize(dim);
Just set the text of the button or add an Icon to the button and the button will determine its own preferred size.
Also, you really should call your "menu" panel a "toolbar" panel. Swing already supports menus and there is a special method to add a menu bar to the frame. Read the section from the Swing tutorial on How to Use Menus for more information.

Should the panels be fields inside the frame?

I created a frame with almost 20 panels inside (all with different kind and characteristics) simply creating them and adding them to the content Panel and remembering his order number for accessing them.
But now I'm trying to generate an UML diagram from the source code and I noticed that i don't have any reference to this panels inside the frame. Should I create 20 field panels and reference them one by one? Or It's just fine? I don't know the right way, thanks!
P.S: I don't know if this matters but my language is Java

The way you write about your panels (all with different kind and characteristics) I suspect that these panels also have different classes.
So to access a specific panel your code probably looks like
((MyPanelType1) getContentPane().getComponent(0)).someMethod();
whereas with fields for every panel
private MyPanelType1 firstPanel;
the code would look like
firstPanel.someMethod();
Now decide which code is easier to read, and decide accordingly.

You can store the panels in JPanel[] array so you can call them any time.
import java.awt.Color;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class TestClass {
static JFrame frame = new JFrame();
static JPanel[] panel_order = new JPanel[20]; // 20 the number of panels you have
//generating the panels
public static void main(String[] args){
frame.setBounds(0, 0, 500, 400);
for(int i=0;i<panel_order.length;i++){
JPanel panel = new JPanel();
// you can set the panel's location like:
panel.setBounds(20*i, 0, 80, 50);
//and border if you are making diagrams
panel.setBorder(BorderFactory.createLineBorder(Color.BLACK));
panel_order[i] = panel;
frame.add(panel);
}
frame.setVisible(true);
//now you can access your panels by calling panel_order[panel_number];
//example display the 5th panel's location
System.out.println(panel_order[5].getLocation());
}
}

How can I change the background color of a jPanel containing JRadioButtons?

I have an java assignment in which I need to have the background color of a GUI change depending on user selected radio buttons listing different colors.
My program has a JFrame to hold everything, then 3 JPanels (1 Instruction area, 1 Radio Button grid, 1 result Textfield) within that frame.
My action listener is currently setting the background color with this statement: getContentPane().setBackground(Color.decode(colorMap.get(btn.getName())));
The background for the JFrame and two of the three panels successfully changes to the correct color, but the panel holding the JRadioButtons will not change at all!
I have tried changing the opaque setting, I have tried setting the panel's background color to (0,0,0,0) but so far none of that is working for me. Does anyone have a suggestion of what I might try or read up on next?
I don't have enough reputation to post a picture but if seeing what I'm talking about helps, let me know and I can email you a screenshot.
Thanks!

You must additionally set all JRadioButtons.setOpaque(false).
Example with one JRadioButton opaque and one non-opaque:
import java.awt.BorderLayout;
import java.awt.Color;
import javax.swing.BoxLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
public class XFrame
extends JFrame
{
public XFrame(String title)
{
super(title);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setLayout(new BorderLayout());
JRadioButton b1 = new JRadioButton("Non opaque button");
// button must not be opaque
b1.setOpaque(false);
// this button is opaque and does not use the background color of the frame
JRadioButton b2 = new JRadioButton("Opaque button");
JPanel p1 = new JPanel();
// panel must be non opaque also
p1.setOpaque(false);
p1.setLayout(new BoxLayout(p1, BoxLayout.Y_AXIS));
p1.add(b1);
p1.add(b2);
add(p1, BorderLayout.CENTER);
getContentPane().setBackground(Color.red);
setSize(200, 200);
}
public static void main(String[] args)
{
XFrame frame = new XFrame("Test");
frame.setVisible(true);
}
}

Aligning JButton to the right

I am creating an interface in java and i want to align the button to the right. I have try but its not working. Can someone tell me how to do it?
import java.awt.Color;
import java.awt.GridLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Button_Alignment extends JFrame{
public JPanel header,body,footer;
public JButton add1;
public JButton save;
public Button_Alignment(){
super("BUTTON");
GridLayout g1 = new GridLayout(3,1);
setLayout(g1);
//////
header = new JPanel();
JButton add1 = new JButton("add");
header.add(add1);
JButton save = new JButton("save");
header.add(save);
//////
add(header);
header.setBackground(Color.cyan);
}
public static void main(String[] args){
Button_Alignment ba = new Button_Alignment();
ba.setSize(400, 400);
ba.setVisible(true);
}
}

Your current layout manager (GridLayout) is being created with 3 rows and a single column. Hence, the components you add to the JFrame will appear vertically from top to bottom. Worse still, GridLayout will aportion space equally amongst all 3 components, meaning that your buttons will stretch in both directions, which is almost certainly not what you require.
I would consider using an alternative layout manager. For simple layouts I tend to favour BorderLayout or FlowLayout. For more complex layouts I lean towards GridBagLayout although there are others who prefer MigLayout.
More information here.

Try like this:
JButton save = new JButton ("save");
setLayout (new BorderLayout ());
add (save, BorderLayout.EAST);

you set GridLayout to the JFrame constructor instead of JPanel (JPanel has by default FlowLayout), I think that
header.setLayout(new GridLayout(3,1));
header.add(add1);
header.add(save);
notice ---> but GridLayout in current ComponentOrientations to start from left to right, then 3rd. grid is empty
then only to add JFrame#add(JPanel), in your case
add(header);

A quick and dirty way is to put the button [or a container immediatly wrapping the button, if you want to add other components on the right next to your button] it in a container that uses the BorderLayout and use the BorderLayout.EAST layout constraint for that button [or wrapping container].