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I've been trying to figure out what is wrong with my code here. The idea is to create a small Paint program and to have red, green, blue, and clear buttons. I have everything that I can think of for it to work, but can't figure out what is wrong with the code. The Program opens, and immediately closes.
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();
}
}
}
852
paint( ) : The paint( ) method is called each time an AWT-based applet's output must be redrawn. This situation can occur for several reasons. For example, the window in which the applet is running may be overwritten by another window and then uncovered. Or the applet window may be minimized and then restored.
At first I create a class that extends JFrame . Then I create a class that extends panel and create a object from this class and add to frame. I want by pressing the right button on keyboard ( VK_RIGHT ) the little rectangles be drawn on panel Within 2 seconds.
What is GUI in Java? GUI (Graphical User Interface) in Java is an easy-to-use visual experience builder for Java applications. It is mainly made of graphical components like buttons, labels, windows, etc. through which the user can interact with an application.
your have to use the visibility properties with frame and panel as well like
frame.setVisible(true);
line g.setVisible(true); is not working for you as you have extended your class jcomponent and your are using frame and not setting its property to set it visible.
Same problem will occure with your panel so your have to set its property as well i-e
panel.setVisible(true);
Here is your full code that is working 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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