Develop Reference

Why do buttons go off screen on Flow Layout?

I'm learning flow layout from Head First Java and I'm trying to have buttons wrap around as it says a Flow Layout should (left to right, top to bottom).
import javax.swing.*;
import java.awt.*;
public class Flow {
public static void main(String[] args) {
Flow gui = new Flow();
gui.go();
}
public void go() {
JFrame frame = new JFrame();
JPanel panel = new JPanel();
JButton buttonOne = new JButton("hello");
JButton buttonTwo = new JButton("this is");
JButton buttowThree = new JButton("woody");
panel.add(buttonOne);
panel.add(buttonTwo);
panel.add(buttonThree);
frame.getContentPane().add(BorderLayout.EAST, panel);
frame.setSize(200,200);
frame.setVisible(true);
}
}
However, when setting the panel on the EAST region of the frame, the buttons go off the screen and don't wrap around. If I set the panel on the NORTH or SOUTH region, I only see two buttons. If I set the panel on the CENTER region, they DO wrap and can see all of them clearly. Why is this?

If you're adding a component to a BorderLayout frame, the East and West regions will let the component get its preferred width. Since the panel contains three buttons and places them side by side, the preferred width of the panel is that of the three buttons side by side. Therefore, it is going "off-the-screen" since that is the preferred width. If you were to a button on to the frame on the EAST region instead and fill it up with enough text, the same would happen. The CENTER region gets whatever is left that the other regions haven't taken up already. Since that is the policy of the CENTER region, the panel does NOT get its preferred width or height, therefore forcing the components of the panel to wrap.
As far as the NORTH and SOUTH regions go, the panel will get its preferred height which is the height of the tallest component (in the example all buttons are the same height). Therefore it sees no reason to wrap. The panel however, DOESN'T get its preferred width. Therefore the buttons are "cut off" since the max width the panel can have is that of the frame. You will notice as the frame resizes, the buttons appear on the screen as space is made available on the panel.

JLabel text Y paint coordinate

The default JLabel draws its text at the middle of its bounds. For example, if height of the label is 20, font height is 14, the Y coordinate would be (20 - 14)/2 = 3. Like this:
What should I do if want to align the text to the TOP of the JLabel bounds? Like this:
UPD:
public class LabelTest extends JFrame {
public LabelTest() {
setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
setSize(500, 500);
setLocationRelativeTo(null);
JPanel contentPanel = new JPanel();
contentPanel.setLayout(new BoxLayout(contentPanel, BoxLayout.X_AXIS));
contentPanel.add(Box.createHorizontalStrut(10));
final JLabel label1 = new JLabel("JLabel");
label1.setVerticalAlignment(SwingConstants.TOP); // by the answer of Kevin Workman, doesn't help
label1.setBorder(BorderFactory.createLineBorder(Color.RED));
label1.setFont(new Font("Arial", Font.PLAIN, 14));
contentPanel.add(label1);
setContentPane(contentPanel);
setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new LabelTest();
}
});
}
}

You should be packing the frame. If you so this, there should be no unused space in the label. If you want empty space, use an empty border
label.setBorder(new EmptyBorder(0, 0, 5, 0));
top, left, bottom, right
Also, don't set sizes, Use Layout Mangers and let them do the sizing for you. Setting sizes will give you. Setting sizes will give you a rigid look that may look and perform differently on different platforms. Layout Managers will allow your GUI to be more fluid and adaptable to different environments.
See Laying out Components Within a Container for more information on working with layouts
Also see Should I avoid the use of set(Preferred|Maximum|Minimum)Size methods in Java Swing?

As always, the API is your best friend: http://docs.oracle.com/javase/7/docs/api/javax/swing/JLabel.html#setVerticalAlignment(int)
Edit- Based on your updated SSCCE, the problem is that your BoxLayout is shrinking the JLabel as small as it will go, so the vertical text position doesn't really matter. Try using a BorderLayout to check that.
The problem is that the insets of the JLabel are adding a small space to the top and bottom of the JLabel, so your text looks centered even though it's at the top. Here's a fix for the insets problem: How to change gap in swing label

How to layout multiple panels on a jFrame? (java)

I am in the process of making my own java socket game. My game is painting alright to the full screen (where it says "paint graphics here", but im painting to the whole jframe at the moment). I want to add a textbox with a scroll bar for displaying only text, not taking any input and another textbox to take text inputs from the user and then a button to send the text, for chat purposes. But onto my question, how do I even start to lay this out? I understand I need a layout, but can someone help me on this? Here is my code at the moment (this code only sets up painting to the whole screen at the moment, need to divide the screen up now like I have in the picture above):
public class Setup extends JFrame implements Runnable{
JPanel panel;
JFrame window;
public Setup(Starter start, JFrame window){
window.setSize(600,500);
window.setLocationRelativeTo(null);
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
window.setResizable(false);
panel = new Display(start);
this.window = window;
}
public void run(){
window.getContentPane().add(panel);
window.setBackground(Color.BLACK);
window.setVisible(true);
}
}
"new Display(start)" - this extends jpanel, its basically where I paint everything graphics wise.
In addition, I've seen people add in different panels but I cant have them be the same size. Like in the picture, the "paint graphics here" panel is the biggest one, and so on.

The JPanel is actually only a container where you can put different elements in it (even other JPanels). So in your case I would suggest one big JPanel as some sort of main container for your window. That main panel you assign a Layout that suits your needs ( here is an introduction to the layouts).
After you set the layout to your main panel you can add the paint panel and the other JPanels you want (like those with the text in it..).
JPanel mainPanel = new JPanel();
mainPanel.setLayout(new BoxLayout(mainPanel, BoxLayout.Y_AXIS));
JPanel paintPanel = new JPanel();
JPanel textPanel = new JPanel();
mainPanel.add(paintPanel);
mainPanel.add(textPanel);
This is just an example that sorts all sub panels vertically (Y-Axis). So if you want some other stuff at the bottom of your mainPanel (maybe some icons or buttons) that should be organized with another layout (like a horizontal layout), just create again a new JPanel as a container for all the other stuff and set setLayout(new BoxLayout(mainPanel, BoxLayout.X_AXIS).
As you will find out, the layouts are quite rigid and it may be difficult to find the best layout for your panels. So don't give up, read the introduction (the link above) and look at the pictures – this is how I do it :)
Or you can just use NetBeans to write your program. There you have a pretty easy visual editor (drag and drop) to create all sorts of Windows and Frames. (only understanding the code afterwards is ... tricky sometimes.)
EDIT
Since there are some many people interested in this question, I wanted to provide a complete example of how to layout a JFrame to make it look like OP wants it to.
The class is called MyFrame and extends swings JFrame
public class MyFrame extends javax.swing.JFrame{
// these are the components we need.
private final JSplitPane splitPane; // split the window in top and bottom
private final JPanel topPanel; // container panel for the top
private final JPanel bottomPanel; // container panel for the bottom
private final JScrollPane scrollPane; // makes the text scrollable
private final JTextArea textArea; // the text
private final JPanel inputPanel; // under the text a container for all the input elements
private final JTextField textField; // a textField for the text the user inputs
private final JButton button; // and a "send" button
public MyFrame(){
// first, lets create the containers:
// the splitPane devides the window in two components (here: top and bottom)
// users can then move the devider and decide how much of the top component
// and how much of the bottom component they want to see.
splitPane = new JSplitPane();
topPanel = new JPanel(); // our top component
bottomPanel = new JPanel(); // our bottom component
// in our bottom panel we want the text area and the input components
scrollPane = new JScrollPane(); // this scrollPane is used to make the text area scrollable
textArea = new JTextArea(); // this text area will be put inside the scrollPane
// the input components will be put in a separate panel
inputPanel = new JPanel();
textField = new JTextField(); // first the input field where the user can type his text
button = new JButton("send"); // and a button at the right, to send the text
// now lets define the default size of our window and its layout:
setPreferredSize(new Dimension(400, 400)); // let's open the window with a default size of 400x400 pixels
// the contentPane is the container that holds all our components
getContentPane().setLayout(new GridLayout()); // the default GridLayout is like a grid with 1 column and 1 row,
// we only add one element to the window itself
getContentPane().add(splitPane); // due to the GridLayout, our splitPane will now fill the whole window
// let's configure our splitPane:
splitPane.setOrientation(JSplitPane.VERTICAL_SPLIT); // we want it to split the window verticaly
splitPane.setDividerLocation(200); // the initial position of the divider is 200 (our window is 400 pixels high)
splitPane.setTopComponent(topPanel); // at the top we want our "topPanel"
splitPane.setBottomComponent(bottomPanel); // and at the bottom we want our "bottomPanel"
// our topPanel doesn't need anymore for this example. Whatever you want it to contain, you can add it here
bottomPanel.setLayout(new BoxLayout(bottomPanel, BoxLayout.Y_AXIS)); // BoxLayout.Y_AXIS will arrange the content vertically
bottomPanel.add(scrollPane); // first we add the scrollPane to the bottomPanel, so it is at the top
scrollPane.setViewportView(textArea); // the scrollPane should make the textArea scrollable, so we define the viewport
bottomPanel.add(inputPanel); // then we add the inputPanel to the bottomPanel, so it under the scrollPane / textArea
// let's set the maximum size of the inputPanel, so it doesn't get too big when the user resizes the window
inputPanel.setMaximumSize(new Dimension(Integer.MAX_VALUE, 75)); // we set the max height to 75 and the max width to (almost) unlimited
inputPanel.setLayout(new BoxLayout(inputPanel, BoxLayout.X_AXIS)); // X_Axis will arrange the content horizontally
inputPanel.add(textField); // left will be the textField
inputPanel.add(button); // and right the "send" button
pack(); // calling pack() at the end, will ensure that every layout and size we just defined gets applied before the stuff becomes visible
}
public static void main(String args[]){
EventQueue.invokeLater(new Runnable(){
#Override
public void run(){
new MyFrame().setVisible(true);
}
});
}
}
Please be aware that this is only an example and there are multiple approaches to layout a window. It all depends on your needs and if you want the content to be resizable / responsive. Another really good approach would be the GridBagLayout which can handle quite complex layouting, but which is also quite complex to learn.

You'll want to use a number of layout managers to help you achieve the basic results you want.
Check out A Visual Guide to Layout Managers for a comparision.
You could use a GridBagLayout but that's one of the most complex (and powerful) layout managers available in the JDK.
You could use a series of compound layout managers instead.
I'd place the graphics component and text area on a single JPanel, using a BorderLayout, with the graphics component in the CENTER and the text area in the SOUTH position.
I'd place the text field and button on a separate JPanel using a GridBagLayout (because it's the simplest I can think of to achieve the over result you want)
I'd place these two panels onto a third, master, panel, using a BorderLayout, with the first panel in the CENTER and the second at the SOUTH position.
But that's me

java use size of JPanel to size components

Is it possible to use the size of a JPanel to set the size of components inside the JPanel? When I try to use getHeight() or getWidth() on the JPanel it always returns 0. I know that it gets it's size once the JFrame is packed, but how would one go about using the dimensions of the JPanel and applying it to a component inside it? Something like this
JPanel panel = new JPanel();
JLabel label = new JLabel();
label.setWidth(panel.getWidth());
panel.add(label);
EDIT:
See sample code below. What should I do if I want my Jlabel to be as wide as my JPanel? Is it wrong to use boxlayout in this case?
public class Main extends JFrame{
public Main(){
JPanel panel = new JPanel();
panel.setLayout(new BoxLayout(panel, BoxLayout.PAGE_AXIS));
panel.setBorder(BorderFactory.createLineBorder(Color.blue));
JLabel label = new JLabel();
label.setBorder(BorderFactory.createLineBorder(Color.red));
label.setText("label1");
label.setMinimumSize(panel.getPreferredSize());
label.setPreferredSize(panel.getPreferredSize());
panel.add(label);
add(panel);
setDefaultCloseOperation(EXIT_ON_CLOSE);
pack();
setSize(500,500);
setVisible(true);
}
public static void main(String[] args)
{
new Main();
}
}

Is it possible to use the size of a JPanel to set the size of components inside the JPanel?
This is the job of the layout manager.
When I try to use getHeight() or getWidth() on the JPanel it always returns 0
When the layout manager is invoked the Container will have a valid size so the layout manager can do its job properly.
There is no reason for you to be playing with sizes. Leave it to the layout managers to do their jobs.
Update:
What should I do if I want my Jlabel to be as wide as my JPanel? Is it wrong to use boxlayout in this case?
The BoxLayout attempts to respect the minimum/maximum size of the component. In you case you should be able to do something like:
JLabel label new JLabel("some text");
label.setBorder(....);
Dimension d = label.getPreferredSize();
d.width = 32767;
label.setMaximumSize( d );
Or maybe a simpler approach is to start with a BorderLayout. You can add the label to the NORTH. Then create another panel and add it to the CENTER.

Of course you can, but be careful that the result depends on the layout manager of your JPanel and on the number of its child components.

Setting the width ignores resizing. LayoutManagers typically ask components for their preferred widths and heights, and expand / contract items to maintain a visually appealing position after the frame has been resized. So, your best option is to leverage the layout manager and report a "preferred width".
You can use setPreferredWidth(...); but, if your preferred width is to change over the run of the program (due to window size changes), you will need to listen to the panel in question and update your button's preferred width as the panel's preferred width changes (this assumes it changes, which might not be true).

Setting the size of panels

I have 3 panels. One is the main panel which holds 2 smaller panels.
For the main panel, I used
setPreferredSize(new Dimension(350, 190));
For the smaller left panel, I used
setPreferredSize(new Dimension(100, 190));
For the smaller right panel, I used
setPreferredSize(new Dimension(250, 190));
but the smaller panels remain the same size. How can I fix this?
This is the code I have in my main Panel.
import model.*;
import java.awt.*;
import javax.swing.*;
public class Panel extends JPanel
{
public Panel(Prison prison)
{
setup();
build(prison);
}
private void setup()
{
setBorder(BorderFactory.createLineBorder(Color.blue));
setLayout(new BorderLayout(1, 1));
setPreferredSize(new Dimension(350, 190));
}
private void build(Prison prison)
{
JTabbedPane tab = new JTabbedPane();
tab.addTab("Input", null, new InputPanel(), "Input");
tab.addTab("Display", null, new DisplayPanel(), "Display");
add(tab);
}
}

Don't do this.
The whole point of layout managers is to allow dynamic resizing, which is necessary not just for user-resizable windows but also changing texts (internationalization) and different default font sizes and fonts.
If you just use the layout managers correctly, they will take care of panel sizes. To avoid having your components stretched out all over the screen when the user increases the window size, have an outermost panel with a left-aligned FlowLayout and the rest of the UI as its single child - that will give the UI its preferred size and any surplus is filled with the background color.

It looks like you're using a GridLayout, or perhaps a FlowLayout, neither being what you want. You probably want to use a BoxLayout, which respects its components preferred sizes.
final JPanel p = new JPanel();
p.setLayout(new BoxLayout(p, BoxLayout.X_AXIS));
p.add(leftPanel);
p.add(mainPanel);
p.add(rightPanel);

also- that is the preferred size. if you don't want to allow resizing, you can also set the maximum sizes as well.
if you're able, you may want to check out the MIG layout, but BoxLayout is also easy to use and in the java toolkit already.

It's this one.
buttonPanel = new JPanel();
buttonPanel.setSize(new Dimension(30, 100));
Don't let the layout manager adjust your sizes.