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Custom JComponent (A Line) Doesn't Show Up On JPanel

It shows the line without jpanel on jframe, but it doesn't when I add it to jpanel. I've tried setting the layout manager of jpanel to null but no result. I want to use JComponents for drawing lines because I want them clickable.
Main.java file:
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
class Main {
public static void main(String[] args) {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
frame.setSize(500, 500);
//Parent Panel
JPanel panel = new JPanel();
panel.setBackground(Color.YELLOW);
panel.setLayout(null);
//Add Line To Panel
Line line = new Line(new Point2D.Double(20,20), new Point2D.Double(180,180));
panel.add(line);
panel.repaint();
frame.add(panel);
frame.setVisible(true);
}
}
class Line extends JComponent {
private final Point2D start, end;
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setColor(Color.BLUE);
g2.setStroke(new BasicStroke(2.0F));
g2.draw(new Line2D.Double(start,end));
}
public Line( Point2D start, Point2D end){
this.start = start;
this.end = end;
addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
System.out.println("mouse clicked");
}
});
}
}

It shows the line without jpanel on jframe, but it doesn't when I add it to jpanel
Swing components are responsible for determining their own preferred size.
When you add a component to a panel, the layout manager will then set the size/location of the component based on the rules of the layout manager.
When you add a component to the frame you really add it to the content pane of the frame which is a Jpanel which uses a BorderLayout by default. So the component is sized to fill the space available in the frame.
panel.setLayout(null);
You then added the component to a panel with a null layout. Now you are responsible for setting the size/location of the component. If you don't the size is (0, 0) so there is nothing to paint.
You should override the getPreferredSize() method of your class to return the preferred size of the component. Then layout managers can do their job.
If you really need a null layout, then the size of the component should be set in the application code, not it the Line class itself.
But now my line has a big container that listens for any clicks,
If you want hit detection then you override the contains(...) method.
Here is a basic example implementing the above suggestions:
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import java.awt.Rectangle;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Line extends JComponent
{
private Line2D.Double line;
public Line( Point2D start, Point2D end)
{
line = new Line2D.Double(start, end);
addMouseListener(new MouseAdapter()
{
#Override
public void mouseClicked(MouseEvent e)
{
System.out.println("mouse clicked");
}
});
}
#Override
protected void paintComponent(Graphics g)
{
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setColor( Color.BLUE );
g2.setStroke( new BasicStroke(2.0F) );
g2.draw( line );
}
#Override
public Dimension getPreferredSize()
{
Rectangle bounds = line.getBounds();
int width = bounds.x + bounds.width;
int height = bounds.y + bounds.height;
return new Dimension(width, height);
}
#Override
public boolean contains(int x, int y)
{
double distance = line.ptSegDist( new Point2D.Double(x, y) );
return distance < 2;
}
public static void main(String[] args)
{
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
frame.setSize(500, 500);
//Parent Panel
JPanel panel = new JPanel();
panel.setBackground(Color.YELLOW);
//Add Line To Panel
Line line = new Line(new Point2D.Double(20,20), new Point2D.Double(180,180));
panel.add(line);
panel.repaint();
frame.add(panel);
frame.setVisible(true);
}
}

Add custom size in Line constructor.
public Line( Point2D start, Point2D end){ ...
this.setSize(200, 200); }
Updated to fit also with painted Graph
Advice to change from JComponent to JPanel in order to see background
import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import javax.swing.JFrame;
import javax.swing.JPanel;
class Main {
public static void main(String[] args) {
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
frame.setSize(500, 500);
//Parent Panel
JPanel panel = new JPanel();
panel.setSize(300,300);
frame.add(panel);
panel.setBackground(Color.YELLOW);
panel.setLayout(null);
//Add Line To Panel
Line line = new Line(new Point2D.Double(20,20), new Point2D.Double(180,180));
panel.add(line);
frame.setVisible(true);
}
}
class Line extends JPanel {
private final Point2D start, end;
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;
g2.setBackground(Color.RED);
g2.setColor(Color.BLUE);
g2.setStroke(new BasicStroke(2.0F));
g2.draw(new Line2D.Double(start,end));
Rectangle r = g2.getClipBounds();
System.out.println(r.x+":"+r.y);
}
public Line( Point2D start, Point2D end){
this.start = start;
this.end = end;
addMouseListener(new MouseAdapter() {
#Override
public void mouseClicked(MouseEvent e) {
System.out.println("mouse clicked at "+e.getX()+":"+e.getY());
}
});
int max_x = (int) Math.max(start.getX(), end.getX());
int max_y = (int) Math.max(start.getY(), end.getY());
System.out.println("max x="+max_y+",y="+max_y);
setSize(max_x,max_y);
setVisible(true);
setBackground(Color.GREEN);
}
}
Note: Only inside_green clicks allowed !

java Swing button action

I am new in java and i wanted to work on a simple paint program using java swing.
my simple paint program should draw a shape like triangle, circle and square whenever i clicked on buttons.
i managed to draw these shapes and print it without buttons but i can not do it using ActionListener?
As you see i have a single button at the moment, i want to draw the oval whenever this button is clicked.
This is the code that i am working on it so far:
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class PaintProject extends JComponent implements ActionListener{
public static void main(String[] args) {
JFrame frame=new JFrame("NEW PAINT PROGRAME!");
JButton button1=new JButton("ADD");
PaintProject paint=new PaintProject();
frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
frame.setLayout(new FlowLayout());
frame.add(paint);
frame.add(button1);
frame.pack();
frame.setVisible(true);
}
#Override
public Dimension getPreferredSize(){
return new Dimension(500,500);
}
#Override
protected void paintComponent(Graphics g){
super.paintComponent(g);
g.setColor(Color.red);
g.fillOval(0,0, 100, 100);
}
#Override
public void actionPerformed(ActionEvent e) {
}
}

Could you please take following steps:
Step 1:
Insert button1.addActionListener(paint); just after PaintProject paint=new PaintProject(); in the main method of PaintProject.java
Step 2:
Remove the method named protected void paintComponent(Graphics g). Instead create following method:
private void drawOval(){
Graphics g = this.getGraphics();
g.setColor(Color.red);
g.fillOval(0,0, 100, 100);
}
Step 3:
Call the above method as follows:
#Override
public void actionPerformed(ActionEvent e) {
drawOval();
}
EDIT:
Following example demonstrates how to draw two shapes when respective buttons are clicked:
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.WindowConstants;
public class PaintProject extends JComponent implements ActionListener {
public static void main(String[] args) {
JFrame frame = new JFrame("NEW PAINT PROGRAME!");
JButton ovalButton = new JButton("Oval");
ovalButton.setActionCommand("Oval");
JButton rectangleButton = new JButton("Rectangle");
rectangleButton.setActionCommand("Rectangle");
PaintProject paint = new PaintProject();
ovalButton.addActionListener(paint);
rectangleButton.addActionListener(paint);
frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
frame.setLayout(new FlowLayout());
frame.add(paint);
frame.add(ovalButton);
frame.add(rectangleButton);
frame.pack();
frame.setVisible(true);
}
#Override
public Dimension getPreferredSize() {
return new Dimension(500, 500);
}
private void drawOval() {
Graphics g = this.getGraphics();
g.setColor(Color.red);
g.fillOval(0, 0, 100, 100);
}
private void drawRectangle() {
Graphics g = this.getGraphics();
g.setColor(Color.green);
g.fillRect(150, 150, 100, 100);
}
#Override
public void actionPerformed(ActionEvent e) {
String command = e.getActionCommand();
if (command.equals("Oval")) {
drawOval();
} else if (command.equals("Rectangle")) {
drawRectangle();
}
}
}

Java is drawing 2 boxes

So I am making a little game to learn some graphical java and I am having trouble with a button. It is drawing 2, one is the correct size and in the correct location and then there is a very small button centered at the top of the application. THere should only be the one button at (0,0,200,50). I do not know what is wrong but here is the code for the button, if you need something more then this let me know!
ImageIcon test = new ImageIcon("nhButton.png");
JButton jb = new JButton(test);
jb.setBounds(0, 0, 200, 50);
jb.setVisible(true);
add(jb);
EDIT1: the 2 classes where error will be: board.java:
import javax.swing.JPanel;
import javax.swing.JButton;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class Board extends JPanel {
public Board() {
}
#Override
public void paintComponent(Graphics g) {
ImageIcon test = new ImageIcon("nhButton.png");
JButton jb = new JButton(test);
jb.setBounds(0, 0, 200, 50);
jb.setVisible(true);
add(jb);
}
private void drawRectangle(Graphics g, int x, int y, int width, int height) {
Graphics2D g2d = (Graphics2D) g;
g2d.drawRect(x, y, width, height);
}
}
and the main:
import java.awt.EventQueue;
import java.awt.GraphicsEnvironment;
import java.awt.Toolkit;
import javax.swing.JFrame;
public class main extends JFrame {
public main() {
initUI();
}
private void initUI() {
add(new Board());
setSize(800, 600);
setTitle("Application");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setLocationRelativeTo(null);
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
main ex = new main();
ex.setVisible(true);
}
});
}
}

If you try to resize window, you will see that buttons are spawning.
This happens because of your paintComponent method, which is called every painting iteration.
You should move button addition, for example, to constructor which is called once:
public Board() {
ImageIcon test = new ImageIcon("nhButton.png");
JButton jb = new JButton(test);
jb.setBounds(0, 0, 200, 50);
jb.setVisible(true);
add(jb);
}

What can cause a Swing application to inconsistently throw null pointer exceptions?

I have a two class project, one class reads one file, and checks each entry in said file against a website, and posts the return data in another file.
If the return data says true(for example), the data point in the file is flashed on the screen. This functionality works.
I invoke this through the following if statement within a while loop.
if (!query.text().contains("unavailable") && !query.text().contains("at least 3 characters long to acquire.") && line != null) {
HitBox h = new HitBox(line); //GUI Class.
fos.write(query.text().getBytes());
fos.write("\n".getBytes());
fos.flush();
}
Below is my GUI class.
import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.io.IOException;
import javax.swing.ImageIcon;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JWindow;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
import javax.swing.UIManager;
public class HitBox {
private Timer t;
JWindow frame = new JWindow();
public HitBox(String s) {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager
.getSystemLookAndFeelClassName());
} catch (Exception ex) {
}
frame.setAlwaysOnTop(true);
t = new Timer(1000 * 5, new ActionListener() {
public void actionPerformed(ActionEvent e2) {
SwingUtilities.getWindowAncestor(frame.getComponent(0))
.dispose();
}
});
}
});
frame.setBackground(new Color(0, 0, 0, 0));
TranslucentPane tp = new TranslucentPane(s);
frame.setContentPane(tp);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
t.start();
}
}
class TranslucentPane extends JPanel {
public TranslucentPane(String s) {
add(new JLabel(s));
setOpaque(false);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
g2d.setComposite(AlphaComposite.SrcOver.derive(0.85f));
g2d.setColor(getBackground());
g2d.fillRect(0, 0, getWidth(), getHeight());
}
}
This happens using the same set of input data, even if I override the web query, and just return a set value, # a random point in runtime, a JWindow will appear, a nullpointer will be thrown (# my call of the start method of my timer object).
This leads me to believe I'm implementing the timer incorrectly; I'm intrigued by how with consistent data, and return, there is variation in the point it throws the nullpointer.
Exception in thread "main" java.lang.NullPointerException
at HitBox.<init>(HitBox.java:51)
at OriginalGangster.main(OriginalGangster.java:38)

You're not starting your GUI on the GUI thread. You need to move it into the Runnable and be sure to start the Timer after it has been constructed.
e.g.,
import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JWindow;
import javax.swing.Timer;
import javax.swing.UIManager;
public class TestHitBox {
public static void main(String[] args) {
String text = "Hello world! This is Hovercraft!";
int seconds = 5;
float composite = 0.85f;
float points = 48f;
HitBox.showMessage(text, seconds, composite, points);
}
}
class HitBox {
public static void showMessage(final String text, final int seconds, final float composite, final float points) {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager
.getSystemLookAndFeelClassName());
} catch (Exception ex) {
ex.printStackTrace();
}
final JWindow frame = new JWindow();
frame.setBackground(new Color(0, 0, 0, 0));
TranslucentPane tp = new TranslucentPane(text, composite, points);
frame.setContentPane(tp);
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
frame.setAlwaysOnTop(true);
new Timer(1000 * seconds, new TimerListener(frame)).start();
}
});
}
}
class TimerListener implements ActionListener {
private JWindow frame;
public TimerListener(JWindow frame) {
this.frame = frame;
}
#Override
public void actionPerformed(ActionEvent e) {
frame.dispose();
((Timer) e.getSource()).stop();
}
}
#SuppressWarnings("serial")
class TranslucentPane extends JPanel {
private float composite;
public TranslucentPane(String s, float composite, float points) {
this.composite = composite;
JLabel label = new JLabel(s);
label.setFont(label.getFont().deriveFont(Font.BOLD, points));
add(label);
setOpaque(false); // this breaks a rule
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
g2d.setComposite(AlphaComposite.SrcOver.derive(composite));
g2d.setColor(getBackground());
g2d.fillRect(0, 0, getWidth(), getHeight());
g2d.dispose(); // dispose of any graphics we create
}
}
Code updated.
The main code has been moved to a public static method, since this appears to be code to display a message to the user and not to share state with any other code, similar to a JOptionPane message, so I'm making it behave like a JOptionPane.
Timer's ActionListener moved out of constructor for cleanliness.
Added parameters for alpha composite, display time, and message font point size.

Flickering painting using getGraphics

I'm doing a selection tool and I've come with these solutions, in the first using the JPanel getGraphics method I draw a oval wherever the mouse been dragged, in the second I override the paintComponent method to draw the oval.
When I execute the first one there's flickering while dragging the mouse and the drawing is poor, while with the second approach runs perfect. Why does this happen?, if I quit repaint in the first solution it draws the ovals and doesn't 'delete' them.
What are best practices to do something like this?, am I missing something when I draw with getGraphics?.
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class TestGetGraphics extends JFrame {
JPanel canvas;
Painter painter;
class Painter{
void paint( Graphics2D g, Point p ){
g.drawOval(p.x, p.y, 30, 30);
}
}
public TestGetGraphics(){
super();
canvas = new JPanel();
painter = new Painter();
canvas.setPreferredSize( new Dimension(400, 400) );
canvas.setBackground(Color.WHITE);
canvas.addMouseMotionListener(new MouseAdapter() {
public void mouseDragged(MouseEvent me){
painter.paint((Graphics2D) canvas.getGraphics(), me.getPoint());
canvas.repaint();
}
});
add( canvas );
setVisible(true);
pack();
setDefaultCloseOperation(EXIT_ON_CLOSE);
}
public static void main(String [] args){
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new TestGetGraphics();
}
});
}
}
This is the paintComponent approach:
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class TestPaintComponent extends JFrame {
JPanel canvas;
Painter painter;
class Painter{
Point p;
void paint( Graphics2D g ){
if( p != null )
g.drawOval(p.x, p.y, 30, 30);
}
void setPoint( Point p ){
this.p = p;
}
}
public TestPaintComponent(){
super();
canvas = new JPanel(){
#Override
public void paintComponent(Graphics g){
super.paintComponent(g);
painter.paint((Graphics2D) g);
}
};
painter = new Painter();
canvas.setPreferredSize( new Dimension(400, 400) );
canvas.setBackground(Color.WHITE);
canvas.addMouseMotionListener(new MouseAdapter() {
public void mouseDragged(MouseEvent me){
painter.setPoint(me.getPoint());
canvas.repaint();
}
});
add( canvas );
setVisible(true);
pack();
setDefaultCloseOperation(EXIT_ON_CLOSE);
}
public static void main(String [] args){
SwingUtilities.invokeLater(new Runnable() {
#Override
public void run() {
new TestPaintComponent();
}
});
}
}

Don't call getGraphics() on a component. Instead, extend the component and override paintComponent(). More info here: http://docs.oracle.com/javase/tutorial/uiswing/painting/