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GUI program for Java - drawing program

I tried to figure out what was wrong with my code here. The idea is to create a small Paint program and have red, green, blue and transparent buttons. I have everything I can come up with for this, but I can’t understand what is wrong with the code. The program opens and closes immediately.

import java.awt.*; import java.awt.event.*; import javax.swing.*; public class Paint{ public static void main(String[] args){ gui g = new gui(); g.setVisible(true); } } public class gui extends JComponent implements ActionListener{ JButton red, green, blue, clear; Image image; Graphics2D draw; int x, y, prevX, prevY; gui(){ JFrame frame = new JFrame("Paint"); Container content = frame.getContentPane(); content.setLayout(new BorderLayout()); setDoubleBuffered(false); JPanel panel = new JPanel(); content.add(panel, BorderLayout.SOUTH); panel.setPreferredSize(new Dimension(32, 68)); panel.setMinimumSize(new Dimension(32, 68)); panel.setMaximumSize(new Dimension(32, 68)); red = new JButton("Red"); green = new JButton("Green"); blue = new JButton("Blue"); clear = new JButton("Clear"); red.setPreferredSize(new Dimension(50, 16)); green.setPreferredSize(new Dimension(50,16)); blue.setPreferredSize(new Dimension(50, 16)); panel.add(red); panel.add(green); panel.add(blue); panel.add(clear); red.addActionListener(this); green.addActionListener(this); blue.addActionListener(this); clear.addActionListener(this); frame.setSize(500, 500); addMouseListener(new MouseAdapter(){ public void mousePressed(MouseEvent e){ prevX = e.getX(); prevY = e.getY(); } }); addMouseMotionListener(new MouseMotionAdapter(){ public void mouseDragged(MouseEvent e){ x = e.getX(); y = e.getY(); draw.drawLine(prevX, prevY, x, y); repaint(); prevX = x; prevY = y; } }); } public void paintComponent(Graphics g){ if(image==null){ image = createImage(getSize().width, getSize().height); draw = (Graphics2D)image.getGraphics(); draw.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); draw.setPaint(Color.white); draw.fillRect(0, 0, getSize().width, getSize().height); draw.setPaint(Color.black); repaint(); } g.drawImage(image, 0, 0, null); } public void actionPerformed(ActionEvent e) { if( e.getSource()==red){ draw.setPaint(Color.red); repaint(); } if( e.getSource()==green){ draw.setPaint(Color.green); repaint(); } if( e.getSource()==blue){ draw.setPaint(Color.blue); repaint(); } if( e.getSource()==clear){ draw.setPaint(Color.white); draw.fillRect(0, 0, getSize().width, getSize().height); draw.setPaint(Color.black); repaint(); } } }
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you need to use the visibility properties with the frame and panel, as well

 frame.setVisible(true);

line g.setVisible(true); does not work for you, since you have expanded your jcomponent class, and you are using a frame and not setting its property to make it visible.

The same problem will occur with your panel, so you should also set its ie property

 panel.setVisible(true);

Here is your complete code that works after adding these properties

 import java.awt.BorderLayout; import java.awt.Color; import java.awt.Container; import java.awt.Dimension; import java.awt.Graphics; import java.awt.Graphics2D; import java.awt.Image; import java.awt.RenderingHints; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.awt.event.MouseAdapter; import java.awt.event.MouseEvent; import java.awt.event.MouseMotionAdapter; import javax.swing.JButton; import javax.swing.JComponent; import javax.swing.JFrame; import javax.swing.JPanel; public class Paint{ public static void main(String[] args){ gui g = new gui(); g.setVisible(true); } } class gui extends JComponent implements ActionListener{ JButton red, green, blue, clear; Image image; Graphics2D draw; int x, y, prevX, prevY; gui(){ JFrame frame = new JFrame("Paint"); Container content = frame.getContentPane(); content.setLayout(new BorderLayout()); setDoubleBuffered(false); JPanel panel = new JPanel(); content.add(panel, BorderLayout.SOUTH); panel.setPreferredSize(new Dimension(32, 68)); panel.setMinimumSize(new Dimension(32, 68)); panel.setMaximumSize(new Dimension(32, 68)); red = new JButton("Red"); green = new JButton("Green"); blue = new JButton("Blue"); clear = new JButton("Clear"); red.setPreferredSize(new Dimension(50, 16)); green.setPreferredSize(new Dimension(50,16)); blue.setPreferredSize(new Dimension(50, 16)); panel.add(red); panel.add(green); panel.add(blue); panel.add(clear); panel.setVisible(true); red.addActionListener(this); green.addActionListener(this); blue.addActionListener(this); clear.addActionListener(this); frame.setSize(500, 500); frame.setVisible(true) ; addMouseListener(new MouseAdapter(){ public void mousePressed(MouseEvent e){ prevX = e.getX(); prevY = e.getY(); } }); addMouseMotionListener(new MouseMotionAdapter(){ public void mouseDragged(MouseEvent e){ x = e.getX(); y = e.getY(); draw.drawLine(prevX, prevY, x, y); repaint(); prevX = x; prevY = y; } }); } public void paintComponent(Graphics g){ if(image==null){ image = createImage(getSize().width, getSize().height); draw = (Graphics2D)image.getGraphics(); draw.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); draw.setPaint(Color.white); draw.fillRect(0, 0, getSize().width, getSize().height); draw.setPaint(Color.black); repaint(); } g.drawImage(image, 0, 0, null); } public void actionPerformed(ActionEvent e) { if( e.getSource()==red){ draw.setPaint(Color.red); repaint(); } if( e.getSource()==green){ draw.setPaint(Color.green); repaint(); } if( e.getSource()==blue){ draw.setPaint(Color.blue); repaint(); } if( e.getSource()==clear){ draw.setPaint(Color.white); draw.fillRect(0, 0, getSize().width, getSize().height); draw.setPaint(Color.black); repaint(); } } }
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