Develop Reference

Having troubles rendering rectangle on button press

I am trying to add a Rectangle in the panel by button press and remove it with another one. It should work but it doesn't render anything, and I absolutely don't know why.
Can someone explain what I am doing wrong and give me some nice tips what I can improve with my code?
public class GUI extends JPanel {
public static boolean isRecVisible = false;
public static void main(String[] args) {
createGui();
}
#Override
protected void paintComponent(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
super.paintComponent(g);
g2d.drawRect(10, 10, 200, 200);
}
public static void createGui() {
int frameWidth = 550;
int frameHeight = 400;
int buttonWidth1 = 250;
int buttonHeight1 = 30;
int buttonWidth2 = 500;
int buttonHeight2 = 30;
int displayWidth = frameWidth - 20;
int displayHeight = frameHeight - 105;
GUI drawRec = new GUI();
JFrame f = new JFrame("Rectangle");
JPanel p = new JPanel();
JPanel display = new JPanel();
JButton addRec = new JButton("Add Rectangle");
JButton removeRec = new JButton("Remove Rectangle");
JButton colorRec = new JButton("Color Rectangle");
f.add(p);
p.add(addRec);
p.add(removeRec);
p.add(colorRec);
p.add(display);
display.setBackground(Color.LIGHT_GRAY);
f.setSize(frameWidth, frameHeight);
f.setLocationRelativeTo(null);
f.setResizable(false);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setVisible(true);
display.setBounds(frameWidth / 2 - displayWidth / 2, 10, displayWidth, displayHeight);
addRec.setBounds(frameWidth / 2 - buttonWidth1 / 2 - 250 / 2, frameHeight - 85, buttonWidth1, buttonHeight1);
removeRec.setBounds(frameWidth / 2 - buttonWidth1 / 2 + 250 / 2, frameHeight - 85, buttonWidth1, buttonHeight1);
colorRec.setBounds(frameWidth / 2 - buttonWidth2 / 2, frameHeight - 60, buttonWidth2, buttonHeight2);
addRec.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
if (isRecVisible == false) {
isRecVisible = true;
display.add(drawRec);
display.repaint();
System.out.println("Rectangle has been drawn!");
} else {
System.out.println("Rectangle has already been drawn!");
return;
}
}
});
removeRec.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
if (isRecVisible == true) {
isRecVisible = false;
System.out.println("Rectangle has been removed!");
} else {
System.out.println("Rectangle has already been removed");
return;
}
}
});
}
}

display.add(drawRec);
display.repaint();
When you add (or remove) components to a visible frame then the basic logic is:
display.add(...);
display.revalidate();
display.repaint(); // sometimes needed
The revalidate() is the key method because it invokes the layout manager so the size/location of the component can be set.
However, that still won't fix the problem because your custom panel doesn't have a preferred size, so there is nothing to paint for your component.
You need to override the getPreferredSize() method of your custom panel to return the preferred size of your custom component. So in your case you might set the preferred size to be (220, 220) so the rectangle is centered in the panel.
Read the section from the Swing tutorial on Custom Painting for more information and complete working examples.
Note: the tutorial example will also show you how to better structure your code to make sure the GUI is created on the Event Dispatch Thread.

Rather than adding or removing components, it would make more sense here to add the custom painted panel on construction, and use the isRecVisible boolean as a flag to test for drawing the rectangle.
Something like shown here:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class GUI extends JPanel {
public static boolean isRecVisible = false;
public static void main(String[] args) {
createGui();
}
#Override
protected void paintComponent(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
super.paintComponent(g);
if (isRecVisible) {
g2d.drawRect(10, 10, 200, 200);
}
}
#Override
public Dimension getPreferredSize() {
return new Dimension(600,400);
}
public static void createGui() {
int frameWidth = 550;
int frameHeight = 400;
GUI drawRec = new GUI();
drawRec.setBackground(Color.LIGHT_GRAY);
JFrame f = new JFrame("Rectangle");
JPanel p = new JPanel();
JButton addRec = new JButton("Add Rectangle");
JButton removeRec = new JButton("Remove Rectangle");
JButton colorRec = new JButton("Color Rectangle");
f.add(p, BorderLayout.PAGE_START);
p.add(addRec);
p.add(removeRec);
p.add(colorRec);
f.add(drawRec);
f.setSize(frameWidth, frameHeight);
f.setLocationRelativeTo(null);
f.setResizable(false);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.setVisible(true);
addRec.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
isRecVisible = true;
drawRec.repaint();
}
});
removeRec.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
isRecVisible = false;
drawRec.repaint();
}
});
}
}

How to indeed center object in a JFrame?

I have a class which extends a Jframe, and i have it centered using setLocationRelativeTo(null);. The layouManager is null aswell.
My JFrame:
mport com.sxf.protocol.chat.util.window.AbstractField;
import javax.swing.*;
import javax.swing.border.LineBorder;
import java.awt.*;
public class Field extends AbstractField {
private Container cp;
public Field() {
super("Test");
buildWindow();
}
private void buildWindow() {
setDefaultCloseOperation(DISPOSE_ON_CLOSE);
setPreferredSize(new Dimension(frameWidth, frameHeight));
setResizable(false);
cp = getContentPane();
cp.setLayout(null);
initComponents();
pack();
setLocationRelativeTo(null);
setVisible(true);
}
private void initComponents() {
JLabel label = new JLabel("Test", SwingConstants.CENTER);
JLabel border = new JLabel("");
label.setSize(200, 30);
label.setLocation((frameWidth - label.getWidth()) / 2, (frameHeight - label.getHeight()) / 2);
border.setBounds(frameWidth / 2, 0, frameWidth / 2, frameHeight);
label.setBorder(new LineBorder(new Color(0, 0, 0)));
border.setBorder(new LineBorder(new Color(255, 0, 0)));
cp.add(label);
cp.add(border);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new Field();
}
});
}
}
I added to border to see if its centered correctly or not.
The AbstractField (only some calculations in it):
public abstract class AbstractField extends JFrame {
private final static Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
private static final Dimension frameSize = new Dimension(screenSize.width / 4, screenSize.height / 4);
protected static final int frameWidth;
protected static final int frameHeight;
protected static final int x;
protected static final int y;
static {
frameWidth = frameSize.width;
frameHeight = frameSize.height;
x = (screenSize.width - frameWidth) / 2;
y = (screenSize.height - frameHeight) / 2;
}
public AbstractField(String title) {
super(title);
}
}
But when i try to center my components, e.g. the JLabel, doing
(frame.getWidth - component.getWidth) / 2, and the same for the height, it is not actually centered but a little bit to the right.
Is that due to a native moved beginning of the jframe and can i calculate that?

How to indeed center object in a JFrame?
Indeed add it as the only component added to a JPanel with a GridBagLayout. Use that panel as the content pane.
Example:
import java.awt.*;
import javax.swing.*;
import javax.swing.border.*;
public class CenteredLabel {
private JComponent ui = null;
CenteredLabel() {
initUI();
}
public final void initUI() {
if (ui!=null) return;
ui = new JPanel(new GridBagLayout());
ui.setBorder(new EmptyBorder(4,4,4,4));
JLabel centeredLabel = new JLabel("Test");
centeredLabel.setBorder(new LineBorder(Color.RED));
ui.add(centeredLabel);
}
public JComponent getUI() {
return ui;
}
public static void main(String[] args) {
Runnable r = () -> {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (Exception useDefault) {
}
CenteredLabel o = new CenteredLabel();
JFrame f = new JFrame(o.getClass().getSimpleName());
f.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
f.setLocationByPlatform(true);
f.setContentPane(o.getUI());
f.pack();
f.setMinimumSize(f.getSize());
f.setVisible(true);
};
SwingUtilities.invokeLater(r);
}
}

Adding two JPanels to JFrame, only one is visible

I have the following problem, when i want to add 2JPanels to my JFrame only one is visible, depending on which I added to the frame last. I overrided the JPanels default paintComponent() method on both of the JPanels. How can i fix this?
Code snippet:
Border:
public class BorderDrawer extends JPanel{
private int _width,_height;
BorderDrawer(int width,int height)
{
setOpaque(false);
_width = width;
_height = height;
}
#Override
protected void paintComponent(Graphics g) {
final int BUTTON_WIDTH = 20,BUTTON_HEIGHT = 20;
int MINES_HORIZONTALLY = _width;
int MINES_VERTICALLY = _height;
super.paintComponent(g);
try{
BufferedImage topLeftCorner = ImageIO.read(this.getClass().getResource("topLeftCorner.png"));
g.drawImage(topLeftCorner, 0, 0, null);
....// drawing other border components
}
}
Clock:
public class GraphicTimer extends JPanel{
Timer _aktTimer = null;
int seconds;
int _width = 0;
GraphicTimer(int width)
{
setSize(52, 31);
setOpaque(false);
_width = width;
int delay = 1000; //milliseconds
_aktTimer = new Timer(delay, taskPerformer);
}
#Override
protected void paintComponent(Graphics g)
{
super.paintComponent(g);
try
{
final int BUTTON_WIDTH = 20,BUTTON_HEIGHT = 20;
int MINES_HORIZONTALLY = _width;
int HORIZONTAL_ENDING = 15+BUTTON_WIDTH*MINES_HORIZONTALLY;
BufferedImage clock = ImageIO.read(this.getClass().getResource("clock.png"));
g.drawImage(clock,HORIZONTAL_ENDING-54,22, null);
}
catch(IOException ex)
{
ex.printStackTrace();
}
}
....
}
JFrame:
public class DrawerField extends JFrame implements Serializable{
//...
public DrawerField()
{
super("MineSweeper");
_FIELD = new Field();
constructorInit();
}
public void constructorInit()
{
_buttons = new FieldButton[_height][_width];
_isMouseEventEnabled = true;
fieldPanel = new JPanel();
smilePanel = new JPanel();
//INITS
int fieldSizeWidth = (_width)*20;
int fieldSizeHeight = (_height)*20; // Magic size
fieldPanel.setSize(fieldSizeWidth,fieldSizeHeight); // 20x20
fieldPanel.setLocation(15, 70);
fieldPanel.setLayout(new GridLayout(_width,_height));
int fullWindowWidth = fieldSizeWidth+36;
int fullWindowHeight = fieldSizeHeight+142;
setSize(fullWindowWidth,fullWindowHeight);
setResizable(false);
setDefaultCloseOperation(EXIT_ON_CLOSE);
restartButton = new RestartButton(this);
smilePanel.setSize(34,34);
smilePanel.add(restartButton);
smilePanel.setLayout(new GridLayout(1,1));
smilePanel.setLocation((int)fullWindowWidth/2-(34/2)-1,20);
///INITIALS
for(int i = 0; i < _height; i++)
{
for(int j = 0; j < _width ; j++)
{
_buttons[i][j] = new FieldButton(_hidden[i][j],true,i,j,this);
fieldPanel.add(_buttons[i][j]);
}
}
add(smilePanel);
add(fieldPanel);
borderDrawer = new BorderDrawer(_width,_height);
_graphicTimer = new GraphicTimer(_width);
_graphicTimer.start();
add(_graphicTimer); // This is the two lines which change the result
add(borderDrawer);
MenuBar menuBar = new MenuBar(this);
setJMenuBar(menuBar);
setVisible(true);
}
//...
}
Easier and compilable example:
public class Main {
public static void main(String[] args)
{
JFrame frame = new JFrame();
frame.setSize(500, 500);
MyPanel panel1 = new MyPanel(30,30);
frame.add(panel1);
MyPanel panel2 = new MyPanel(70,30);
frame.add(panel2);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.repaint();
frame.setVisible(true);
}
public static class MyPanel extends JPanel
{
int _x,_y;
MyPanel(int x, int y)
{
_x = x; _y = y;
}
#Override
public void paint(Graphics g) {
g.drawOval(_x,_y,20,20);
}
}
}
My main goal is to add 2 circles to the JFrame without using any Layout.( As you can see in the example above I already have a lot of things on my JFrame that's why I don'T want to use layouts). The problem is the same in this example, when i add the 2nd circle the first is disappearing.

Its simple. Adding a panel in a frame adds it to the content pane of the frame. This contentpane has a default layout of BorderLayout which means, every time you add a panel, it gets added to the center of the content pane and gets replaces the previous one. This is the reason why you see only the last one. Its always good to use a Jpanel set to the layout of your choice put everything that needs to be shown on the screen in that panel. If you don't want to do that, you may also call getContentPane() from the frame and play with the returned instance of JPanel.

Here is the example code for you:
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.GridLayout;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Frame extends JFrame {
public Frame() {
setTitle("Two panels");
setSize(new Dimension(500,500));
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//Here goes your code
JPanel p= (JPanel) getContentPane();
p.setLayout(new GridLayout(1,2)); //set your own layout
p.add(new MyPanel(Color.BLUE)); //add panel with blue border
p.add(new MyPanel(Color.GREEN));//add panel with green border
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
Frame f= new Frame();
f.setVisible(true);
}
});
}
}
class MyPanel extends JPanel {
public MyPanel(Color color) {
setBorder(BorderFactory.createLineBorder(color));
}
}
Run it and see... You should be able to see something like this:

Is it possible not to inherit from JPanel to inner class?

Good morning. I want to write a program that scale up a filledgraphic with the help of JSlider. When ActPanel and Contour were inner classes of Lab4, they at least showed themselves on a JFrame. But there was a huge problem with passing Radius and repainting. I refrained from using inner classes, but it gave me no more ActPanel and Contour on the screen.
Here is code's most important part
class ActPanel extends JPanel implements ChangeListener {
public Contour cont;
public ActPanel(Contour contour) {
super(new FlowLayout());
cont = contour;
JSlider slider = new JSlider(JSlider.HORIZONTAL, 0, 250, 50);
slider.addChangeListener(this);
JButton button = new JButton("display mark");
}
public void stateChanged(ChangeEvent e) {
if (e.getSource() instanceof JSlider) {
JSlider source = (JSlider)e.getSource();
if (!source.getValueIsAdjusting()) {
int R = (int)source.getValue();
cont.setR(R);
cont.repaint();
}
}
}
}
class Contour extends JPanel {
private static final int pointCount = 9;
public void paintComponent(Graphics gfx) {
super.paintComponent(gfx);
Graphics2D g = (Graphics2D) gfx;
GeneralPath fpolygon = new GeneralPath(GeneralPath.WIND_EVEN_ODD, pointCount);
fpolygon.moveTo(Float.valueOf((float)R+250), Float.valueOf(250.0f));
fpolygon.lineTo(Float.valueOf(250.0f), Float.valueOf(250.0f));
//some drawing
}
private int R;
public void setR(int R) {
this.R = R;
}
public int getR() {
return R;
}
}
public class Lab4 {
private static void addComponentsToPane(Container pane) {
if (!(pane.getLayout() instanceof BorderLayout)) {
pane.add(new JLabel("Container doesn't use BorderLayout!"));
return;
}
Contour cont = new Contour();
ActPanel bottom = new ActPanel(cont);
pane.add(bottom, BorderLayout.PAGE_END);
cont.setPreferredSize(new Dimension(500,500));
pane.add(cont, BorderLayout.LINE_END);
}
private static void createAndShowGUI() {
JFrame frame = new JFrame("Lab4");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
addComponentsToPane(frame.getContentPane());
frame.pack();
frame.setVisible(true);
}
public static void main(String [] arg) {
SwingUtilities.invokeLater(
new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}
And that's a full version
import java.io.*;
import java.util.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import java.awt.geom.*;
class ActPanel extends JPanel implements ChangeListener {
public Contour cont;
public ActPanel(Contour contour) {
super(new FlowLayout());
cont = contour;
JSlider slider = new JSlider(JSlider.HORIZONTAL, 0, 250, 50);
slider.addChangeListener(this);
JButton button = new JButton("display mark");
}
public void stateChanged(ChangeEvent e) {
if (e.getSource() instanceof JSlider) {
JSlider source = (JSlider)e.getSource();
if (!source.getValueIsAdjusting()) {
int R = (int)source.getValue();
cont.setR(R);
cont.repaint();
}
}
}
}
class Contour extends JPanel {
private static final int pointCount = 9;
public void paintComponent(Graphics gfx) {
super.paintComponent(gfx);
double kappa = 0.5522847498;
Graphics2D g = (Graphics2D) gfx;
g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
GeneralPath fpolygon = new GeneralPath(GeneralPath.WIND_EVEN_ODD, pointCount);
fpolygon.moveTo(Float.valueOf((float)R+250), Float.valueOf(250.0f));
fpolygon.lineTo(Float.valueOf(250.0f), Float.valueOf(250.0f));
fpolygon.lineTo(Float.valueOf(250.0f), Float.valueOf((float)250-R/2));
fpolygon.curveTo(
Float.valueOf((float)((-R/2)*kappa+250)),Float.valueOf((float)(-R/2)+250),
Float.valueOf((float)(-R/2)+250),Float.valueOf((float)((-R/2)*kappa)+250),
Float.valueOf((float)-R/2+250), Float.valueOf(250.0f));
fpolygon.lineTo(Float.valueOf((float)-R+250), Float.valueOf(250.0f));
fpolygon.lineTo(Float.valueOf((float)-R+250), Float.valueOf((float)R+250));
fpolygon.lineTo(Float.valueOf(250.0f), Float.valueOf((float)R+250));
fpolygon.lineTo(Float.valueOf(250.0f), Float.valueOf((float)R/2+250));
fpolygon.lineTo(Float.valueOf((float)R+250), Float.valueOf(250.0f));
fpolygon.closePath();
g.setPaint(Color.red);
g.fill(fpolygon);
g.setPaint(Color.black);
g.draw(fpolygon);
}
private int R;
public void setR(int R) {
this.R = R;
}
public int getR() {
return R;
}
}
public class Lab4 {
private static void addComponentsToPane(Container pane) {
if (!(pane.getLayout() instanceof BorderLayout)) {
pane.add(new JLabel("Container doesn't use BorderLayout!"));
return;
}
Contour cont = new Contour();
ActPanel bottom = new ActPanel(cont);
pane.add(bottom, BorderLayout.PAGE_END);
JList<Integer> xList = new JList<Integer>(new Integer[] {4,2,5,1,-5,-1,-4});
pane.add(xList, BorderLayout.LINE_START);
JPanel yPanel = new JPanel(new FlowLayout(FlowLayout.LEFT));
yPanel.add(new Label("x\\y"));
yPanel.add(new JCheckBox("5"));
yPanel.add(new JCheckBox("1"));
yPanel.add(new JCheckBox("-5"));
yPanel.add(new JCheckBox("2"));
yPanel.add(new JCheckBox("-5"));
yPanel.add(new JCheckBox("-1"));
yPanel.add(new JCheckBox("4"));
pane.add(yPanel, BorderLayout.PAGE_START);
cont.setPreferredSize(new Dimension(500,500));
pane.add(cont, BorderLayout.LINE_END);
}
private static void createAndShowGUI() {
JFrame frame = new JFrame("Lab4");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
addComponentsToPane(frame.getContentPane());
frame.pack();
frame.setVisible(true);
}
public static void main(String [] arg) {
SwingUtilities.invokeLater(
new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}

You never add the any component to the ActPanel:
public ActPanel(Contour contour) {
super(new FlowLayout());
...
// you're missing the following lines:
this.add(slider);
this.add(button);
So it is in the frame, but empty.
The Contour panel is also in the frame. Add these lines to it, and you'll see it:
public Contour() {
setBackground(Color.BLUE);
}

paintComponent not changing shape

can someone take a look at my code below and tell me why, when I change the following two statements, I do not see a change on the rectangle that is painted. So if I change:
g.setColor(Color.black);
g.fillRect(l, w, 100, 100);
The program still prints a black rectangle with the same dimensions and in the same position that I first started with even though I change color to yellow or try to change the dimensions or location. I am BlueJ. The following is my full code:
import java.awt.*;
import javax.swing.*;
public class SwingPaintDemo2 extends JComponent {
public static boolean isWall = true;
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
private static void createAndShowGUI() {
//System.out.println("Created GUI on EDT? "+
//SwingUtilities.isEventDispatchThread());
JFrame f = new JFrame("Swing Paint Demo");
JPanel MyPanel = new JPanel();
MyPanel.setBorder(BorderFactory.createEmptyBorder(1000, 1000, 1000, 1000));
MyPanel.setPreferredSize(new Dimension(250, 200));
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.add(new MyPanel());
f.pack();
f.setVisible(true);
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
int l = 10;
int w = 10;
g.setColor(Color.black);
g.fillRect(l, w, 100, 100);
}
}
Any advice would be appreciated.

Your SSCCE doesnt compile where is MyPanel class or did you mean new SwingPaintDemo2()?
On the assumption you meant new SwingPaintDemo2():
The code does work just fine but the JFrame is sized very small:
because you dont give it any size and none of its components have a size as they do not have any components added to them, thus we must make the JComponent return a correct size so when we call pack() our JFrame is sized correctly
Solution
override getPreferredSize() of JComponent to return a width and height which fits all drawings.
Some suggestions though:
Dont extend JComponent rather extend JPanel
Here is an example (your code with above fixes implemented):
import java.awt.*;
import javax.swing.*;
public class SwingPaintDemo2 extends JPanel {
public static boolean isWall = true;
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
private static void createAndShowGUI() {
//System.out.println("Created GUI on EDT? "+
//SwingUtilities.isEventDispatchThread());
JFrame f = new JFrame("Swing Paint Demo");
JPanel MyPanel = new JPanel();
MyPanel.setBorder(BorderFactory.createEmptyBorder(1000, 1000, 1000, 1000));
MyPanel.setPreferredSize(new Dimension(250, 200));
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.add(new SwingPaintDemo2());
f.pack();
f.setVisible(true);
}
#Override
public void paintComponent(Graphics g) {
super.paintComponent(g);
int l = 10;
int w = 10;
g.setColor(Color.black);
g.fillRect(l, w, 100, 100);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(150, 150);
}
}