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Removing JFrame Border?

I have a Java Swing GUI and everything in my JFrame is offset by a few pixels. On MacOS, I had to offset everything by 12 pixels downward to account for it. On Windows, everything is shifted to the left and downward as well. I discovered that
setUndecorated(true);
removes the JFrame border (which I suspect is the cause of my problems) but it also removes the title bar.
Is there a way I can remove the JFrame border (or some other alternative to make sure everything is centered) and still keep the title bar? I need the title bar so that I can move the JFrame around and have the maximize/minimize/close functions.
Also, the layout is set to null in case that matters. (Everything I'm doing is pixel - based so I cannot set it to anything else).
Thanks.

I found a solution after Googling a bit more. Calling
getContentPane().setPreferredSize(...)
pack();
inside the JFrame constructor will adjust everything so that the titlebar and borders will not impact the view of the content pane.
For anyone else that may need this, you have to set the preferred size of the content pane specifically as that is what you want to appear correctly.
This way you can keep the titlebar and all the normal functionality of a JFrame window that you would otherwise lose with setUndecorated(true);.

The reason why you are adding 12px is because this is consume by the Title and border.
If you use setUndecorated(true) You will loose the title bar and you have to implement the addWindowListener to add a location changing of of an application.
The best way to do is:
Class Main{
public static void main(String[] args){
//JFrame
JFrame frame = new JFrame();
//Create a Main Panel and setPreferred Size and not set Size or set Bound
JPanel mainPanel = new JPanel(); //You value down
mainPanel.setPrefferedSize(new Dimension(x, y));
frame.add(mainPanel);
//and then in last add
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//the pack method help you to setSize of the JFrame According to the
//Component size
frame.pack();
frame.setVisible(true);
}
}

How to add two panels and resize them when frame change sizes?

I have three classes. GameFrame extends JFrame, GamePanel & InfoPanel extend JPanel.
I am looking for the best solution how to add those two panels to frame like on the picture:
The initial size of GamePanel must be (800x800). I would like that when changing the size of the window, both panels also change the size to fit the window. How to do it?

Sounds like you need to set the layout of GameFrame to Border Layout and add InfoPanel to the NORTH of GameFrame and GamePanel to the CENTER. BorderLayout will automatically resize its components to match the size of the JFrame.

How to add a drawing (paint method) and another panel with controls in one frame?

I need to have a JFrame where the upper part is a drawing made by paint() and the lower part is a panel composed of JLabel, JTextField and JButton components.
Is this possible? How am I supposed to do this?

I need to have a Jframe where the upper part is a drawing made by paint() and the lower part is a panel composed of JLabel, JTextField and JButtons.
There is no conflict on what you want to do. You can have a main JPanel with 2 sub panels. One on the top for your drawings, the other at the bottom for containing your JComponents such as JButtons:
The structure in code may look like this:
class MainPanel extends JPanel{
private DrawingSpace drawingSpace; //Customized JPanel for drawing
private JPanel subPanel;
public MainPanel(){
setPreferredSize(new Dimension(400, 400));
initComponents();
}
private void initComponents(){
drawingSpace = new DrawingSpace();
subPanel = new JPanel();
}
}
You can have a customized JPanel as follows (this is optional):
class DrawingSpace extends JPanel
{
public DrawingSpace(){
//Set size..etc
}
#Override
public void paintComponent(Graphics g){
super.paintComponent(g);
//perform your drawings here..
}
}
After the implementations for the JPanels, you can just add an instance of MainPanel to the JFrame:
JFrame frame = new JFrame();
frame.add(new MainPanel());
//Other codes for JFrame not shown here

The soulution suggested by user3437460 (use a JPanel for the upper part, and override the painting methods in that JPanel) is the preferrable way to solve this.
However as you asked for a solution to directly paint the upper part (which is not advised, but there are solutions):
A (nasty) workaround for the question would be overriding the necessary paint method of JFrame, draw your upper part, translate the graphics context by some 100 pixels and call inherited paint methods to draw the bottom part. (Note that you'll have layout manager issues, as the layout manager won't see the 100px height of the upper part. However, if you're using an absolute layout, it could work. Hacks, hacks hacks :(
Another super-hack is to actually make the lower part big enough (if you use absolute layout, position your lower part at y=100px). Then add your own GlassPane and render the content for the upper part (or anywhere) on the glassPane.
Of course you can create a dedicated layout manager, which leaves the top 100 px part empty. Use that layout manager, and then you get some empty space on the top, which you can draw on.
I think now you can agree that the problem is rather "how to put a custom drawn component on the top of the window", which is solved by putting a custom drawn JPanel on the top of the window. Keep it easy! Peace!
ps: override paintComponent() instead of paint() of JPanel. See bottom of http://www.oracle.com/technetwork/java/painting-140037.html

For the painting portion, create a JPanel (or other paintable component) and override the paint method. Use a second JPanel and place all of your other components in that.
From there, check out how to do layout management at https://docs.oracle.com/javase/tutorial/uiswing/layout/using.html#set
The simplest way to do this is to use GridLayout, with the painted panel on the top half and the components panel on the bottom half.

Java Swing JPanel Stay on top of JTable

I have a Jpanel that is used for displaying messages. When mouse enters a JLabel it expands to normal size and when mourse leaves it disappear.
There are overlaps between JTable and JPanel when the JPanel expands to normal size. As JTable's height cannot be changed during runtime only way I can think of is let JPanel stay on top of JTable.
I am very new to Java ans swing. Any idea please?

Sound like you should be using a tool tip.
Edit:
Try using a BorderLayout. Add your main panel to the CENTER and your message panel to the SOUTH. When you make the message panel visible you can revalidate() the main panel and the Center panel will shrink in size to take whatever space is not required by the south panel.

Laying out JPanels to make a simple GUI

first of all, this is more or less my first GUI and ive learned Java for not more then a week, so it might contain some serious programming errors.
What i have right now is:
Buttons and labels are part of OptionPanel and are on the left, DrawingPanel is about 5x5 px in size and is on the right.
What I am trying to do is a simple test, to get me more familiar with the GUI. The rectangle should be movable and re-sizeable by the user when clicking the respective buttons:
http://www.upload.ee/image/612005/JFrame2.jpg
Right now i have:
JFrame MainFrame - Makes JFrame (Not using the setSize function. using .pack() instead. not sure about it)
JPanel MergedPanel - FlowLayout - Adds JPanel OptionsPanel and JPanel DrawingPanel together and gets injected to JFrame MainFrame
JPanel DrawPanel - This JPanel is responsible of drawing the rectangle.
JPanel OptionPanel - FlowLayout - This JPanel is responsible of the buttons.
Help please.

You should never call setSize() in your code. In Java, you use layout managers to do the layout (read that tutorial).
Subclassing JPanel to implement different parts of which the UI is composed is a good practice, but should not be overdone (it's fine to have an UI class that adds 3 other plain JPanel instances to itself for layout purposes).

Check out MiG Layout : one can make pretty easily java layouts with that.