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How to create Canvas object by calling Canvas constructor with arguments in Java?

Could you please help me to know how to
create a ColorImage object by using the default constructor of the ColorImage class?
create a Canvas object by calling the Canvas constructor with arguments. The first and second arguments of the constructor are the width and the height of the ColorImage. The width and height of a ColorImage have obtain by using the getWidth() and getHeight() methods in the ColorImage class.

public class MyPaint {
public static void main(String[] args) {
new PaintFrame("JavaPainter",100,300);
}
}
class MyCanvas extends JPanel implements MouseListener, MouseMotionListener {
private Vector<Point> curve;
private Vector<Vector<Point>> curves;
private Point ptFrom = new Point();
private Point ptTo = new Point();
MyCanvas() {
curve = new Vector<Point>();
curves = new Vector<Vector<Point>>();
this.setPreferredSize(new Dimension(1, 1));
this.addMouseListener(this);
this.addMouseMotionListener(this);
}
public void paintComponent(Graphics g) {
g.setColor(Color.RED);
for (Vector<Point> points : curves) {
Point pt0 = points.get(0);
for (int i = 1; i < points.size(); ++i) {
Point pt = points.get(i);
g.drawLine(pt0.x, pt0.y, pt.x, pt.y);
pt0 = pt;
}
}
}
#Override
public void mousePressed(MouseEvent e) {
ptFrom.x = e.getX();
ptFrom.y = e.getY();
curve.add((Point) ptFrom.clone());
}
#Override
public void mouseReleased(MouseEvent e) {
ptTo.x = e.getX();
ptTo.y = e.getY();
curve.add((Point) ptTo.clone());
curves.add(new Vector<Point>(curve));
curve.clear();
}
#Override
public void mouseDragged(MouseEvent e) {
ptTo.x = e.getX();
ptTo.y = e.getY();
curve.add((Point) ptTo.clone());
Graphics g = getGraphics();
g.setColor(Color.RED);
g.drawLine(ptFrom.x, ptFrom.y, ptTo.x, ptTo.y);
ptFrom.x = ptTo.x;
ptFrom.y = ptTo.y;
}
#Override
public void mouseEntered(MouseEvent e) {
// do nothing
}
#Override
public void mouseExited(MouseEvent e) {
// do nothing
}
#Override
public void mouseClicked(MouseEvent e) {
// do nothing
}
#Override
public void mouseMoved(MouseEvent e) {
// do nothing
}
}
class PaintFrame extends JFrame {
private MyCanvas canvas = new MyCanvas();
PaintFrame(String title) {
super(title);
Container cp = getContentPane();
cp.add(canvas);
setSize(300, 200);
setVisible(true);
}
PaintFrame(String title,Integer length,Integer width) {
super(title);
Container cp = getContentPane();
cp.add(canvas);
setSize(width, length);
setVisible(true);
}
}
From other place http://blog.csdn.net/fduan/article/details/8062556

drag object using mouse Listener

I'm trying to create a program that able the user to drag and drop the oval around in the space. I was able to drag and drop but after I tried do it again on the second run, the oval jump all over the places. I was wondering if anyone know why this happen? Am i missing something? Thank you
public class MoveOval extends JFrame {
private Ellipse2D node = new Ellipse2D.Float(200,200,80,120);
private Point offset;
private int preX,preY;
private Image dbImage;
private Graphics dbg;
Adapter ma = new Adapter();
public static void main(String args[]){
JFrame frame = new MoveOval();
frame.setSize(600,600);
frame.setVisible(true);
}
public MoveOval(){
super("Move Oval");
setDefaultCloseOperation(EXIT_ON_CLOSE);
addMouseListener(ma);
addMouseMotionListener(ma);
}
private class Adapter extends MouseAdapter{
public void mousePressed(MouseEvent e){
if(node.contains(e.getPoint())){
preX = node.getBounds().x-e.getX();
preY = node.getBounds().y-e.getX();
offset = new Point(preX, preY);
}
}
public void mouseDragged(MouseEvent e){
if(node.contains(e.getPoint())){
updateLocation(e);
}
}
public void mouseReleased(MouseEvent e) {
offset=null;
}
}
public void updateLocation(MouseEvent e){
Point to = e.getPoint();
to.x += offset.x;
to.y += offset.y;
Rectangle bounds = node.getBounds();
bounds.setLocation(to);
node.setFrame(bounds);
repaint();
}
public void paint(Graphics g){
dbImage=createImage(getWidth(), getHeight());
dbg = dbImage.getGraphics();
paintComponent(dbg);
g.drawImage(dbImage, 0, 0, this);
}
public void paintComponent(Graphics g){
Graphics2D gd = (Graphics2D)g.create();
gd.setColor(Color.blue);
gd.fill(node);
}
}

Actually a very simple mistake and easy to fix.
public void mousePressed(MouseEvent e){
if(node.contains(e.getPoint())){
preX = node.getBounds().x-e.getX();
preY = node.getBounds().y-e.getX(); // <- That's the bad guy.
offset = new Point(preX, preY);
}
}
It has to be -e.getY() not -e.getX().

Java - boolean set to false with nothing telling it to do so

My boolean drawFlag is being set to false in my code with nothing visible actually telling it to change value to false. This is preventing the code inside method mouseDragged(mouseEvent) to execute. If someone could point out what's making the flag become false so this would stop happening? Thanks.
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class DrawAndDrag {
public static void main(String[] args) throws InterruptedException {
GraphicsFrame window = new GraphicsFrame("Draw Rectangle");
window.init();
}
}
class GraphicsFrame extends JFrame {
public GraphicsFrame(String title) {
super(title);
}
public void init() {
Container pane = this.getContentPane();
pane.add(new GraphicsContent().init());
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setSize(600, 600);
this.setVisible(true);
}
}
class GraphicsContent extends JPanel {
private int xStart, yStart;
private int width, height;
public JPanel init() {
this.setBackground(Color.WHITE);
this.addMouseListener(new MouseDrag());
this.addMouseMotionListener(new MouseDrag());
return this;
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
g.setColor(Color.BLUE);
g.fillRect(xStart, yStart, width, height);
}
class MouseDrag implements MouseListener, MouseMotionListener {
private boolean drawFlag;
public void mousePressed(MouseEvent e) {
if(isOutside(e)) {
this.drawFlag = true;
xStart = e.getX();
yStart = e.getY();
width = 0; height = 0;
System.out.println(drawFlag);
}else {
// this.drawFlag = false;
}
}
public void mouseDragged(MouseEvent e) {
System.out.println(drawFlag);
if(drawFlag) {
width = e.getX() - xStart;
height = e.getY() - yStart;
repaint();
}
}
public boolean isOutside(MouseEvent e) {
int xMin = Math.min(xStart, xStart + width); int yMin = Math.min(yStart, yStart + height);
int xMax = Math.max(xStart, xStart + width); int yMax = Math.max(yStart, yStart + height);
if((e.getX() < xMin || e.getX() > xMax)
|| (e.getY() < yMin || e.getY() > yMax)) {
return true;
}else {
return false;
}
}
public void mouseEntered(MouseEvent e) {}
public void mouseExited(MouseEvent e) {}
public void mouseClicked(MouseEvent e) {}
public void mouseReleased(MouseEvent e) {}
public void mouseMoved(MouseEvent e) {}
}
}

Try to move drawFlag attribute from the inner class MouseDrag to the outer class GraphicsContent as follow
class GraphicsContent extends JPanel {
private int xStart, yStart;
private int width, height;
private volatile boolean drawFlag;
// other code
}

However as you drag, the value is constantly being reported as being false
You've got two listeners. One is a motion listener:
this.addMouseListener(new MouseDrag());
this.addMouseMotionListener(new MouseDrag());
mousePressed will not be called on a motion listener, so it will always be false in the drag event.
I expect what you meant is this:
MouseDrag listener = new MouseDrag();
this.addMouseListener(listener);
this.addMouseMotionListener(listener);

Are you sure you need two MouseDrag elements? I.e. using something like
public JPanel init() {
this.setBackground(Color.WHITE);
MouseDrag md = new MouseDrag();
this.addMouseListener(md);
this.addMouseMotionListener(md);
return this;
}
I can at least plot a blue square....

Java panel interface

Im trying to make a pline drawing program. when I try to repaint all of the lines(after creating a new one) only the last one is draw out.The problem might be in repainting.
Can someone see what I am doing wrong?
Code is here:
public class Kimp extends JFrame {
private ArrayList<Point[]> pointsArray = new ArrayList<>();
private Point points[] = new Point[10000];
private int pointCounter = 0;
public Kimp () {
panel paintArea = new panel();
add(paintArea, BorderLayout.CENTER);
}
private class panel extends JPanel {
public panel () {
HandlerClass handler = new HandlerClass();
this.addMouseListener(handler);
this.addMouseMotionListener(handler);
}
#Override
void paintComponent(Graphics g) {
super.paintComponent(g);
try {
for (Point[] p : pointsArray) {
for(int i = 0; i < p.length; i++) {
if (p[i].x == 0) {
continue;
} else {
if (p[i + 1].x == 0) {
g.setColor(Color.BLUE);
g.drawLine(p[i].x, p[i].y, p[i].x, p[i].y);
} else {
g.setColor(Color.BLUE);
g.drawLine(p[i].x, p[i].y, p[i + 1].x, p[i + 1].y);
}
}
}
}
points = preFill(points);
} catch (NullPointerException e) {
}
}
}
private class HandlerClass implements MouseListener , MouseMotionListener {
#Override
public void mouseDragged(MouseEvent e) {
points[pointCounter++] = e.getPoint();
}
#Override
public void mousePressed(MouseEvent e) {
points[pointCounter] = e.getPoint();
}
#Override
public void mouseMoved(MouseEvent e) {
}
#Override
public void mouseClicked(MouseEvent e) {
}
#Override
public void mouseEntered(MouseEvent e) {
}
#Override
public void mouseExited(MouseEvent e) {
}
}
public static Point[] preFill (Point[] points) {
for (int i = 0; i < points.length; i++) {
points[i] = new Point(-999,-999);
}
return points;
}
}

I quickly rewrote your code to simplify it as much as possible. You may be able to better understand the concepts behind it.
import java.awt.Graphics;
import java.awt.Point;
import java.awt.Color;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
public class Kimp {
public static void main(String[] args) {
JFrame frame = new JFrame("Kimp!");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(800, 600);
frame.setLocationRelativeTo(null);
frame.add(new CanvasPanel());
frame.setVisible(true);
}
}
class CanvasPanel extends JPanel {
private final List<List<Point>> lines = new LinkedList<List<Point>>();
private List<Point> points = new LinkedList<Point>();
public CanvasPanel() {
addMouseListener(mouseAdapter);
addMouseMotionListener(mouseAdapter);
}
#Override
public void paintComponent(Graphics g) {
g.setColor(Color.WHITE);
g.fillRect(0, 0, getWidth(), getHeight());
for (List<Point> line : lines)
drawLine(line, g);
drawLine(points, g);
}
private void drawLine(List<Point> points, Graphics g) {
if (points.size() < 2) return;
Point p1 = points.get(0);
for (int i=1, n=points.size(); i<n; i++) {
Point p2 = points.get(i);
g.setColor(Color.BLUE);
g.drawLine(p1.x, p1.y, p2.x, p2.y);
p1 = p2;
}
}
private MouseAdapter mouseAdapter = new MouseAdapter() {
#Override
public void mousePressed(MouseEvent e) {
points.add(e.getPoint());
repaint();
}
#Override
public void mouseDragged(MouseEvent e) {
points.add(e.getPoint());
repaint();
}
#Override
public void mouseReleased(MouseEvent e) {
if (points.size() > 1) {
lines.add(points);
points = new LinkedList<Point>();
}
}
};
}

private ArrayList<Point[]> pointsArray = new ArrayList<>();
This is a list of Point[]. Here only one private Point points[] = new Point[10000]; is allocated. Which means that each time you add points into pointArray, you are adding the same instance of points.
When you change the elements of points, all the existing Point[] in pointArray is updated. Since all the elements are referring to the same points.
Allocate new Point[] when drawing a new line.

You are resetting your points array every time you painted it (preFillPoints() is called in paint()). Your pointsArray (which should be called pointsList for gods sake) is completely meaninless, you add the same points[] array each time the mouse is released.
The code makes no sense. You only need the list or the array. Not both. Declare a List<Point> (not Point[]) and just add a new Point every time the mouse moves.

Java Challenge on Permitting the User to Draw A Line

My question has been alluded to in java draw line as the mouse is moved, however, I have not advanced far enough into this book to have covered JPanels, JFrames and Points as stated by the prior programmer who asked this question.
Answering this question definitely would help most beginner programmers better understand the graphics class and drawing, an often intricate process, especially for beginners.
According to the text I am using (as I am learning Java on my own), this was the example of how to draw a line using Java:
/*
* LineTest
* Demonstrates drawing lines
*/
import java.awt.*;
public class LineTest extends Canvas {
public LineTest() {
super();
setSize(300, 200);
setBackground(Color.white);
}
public static void main(String args[]) {
LineTest lt = new LineTest();
GUIFrame frame = new GUIFrame("Line Test");
frame.add(lt);
frame.pack();
frame.setVisible(true);
}
public void paint(Graphics g) {
g.drawLine(10, 10, 50, 100);
g.setColor(Color.blue);
g.drawLine(60, 110, 275, 50);
g.setColor(Color.red);
g.drawLine(50, 50, 300, 200);
}
}
The specification is:
Create an application that allows you to draw lines by clicking the initial
point and dragging the mouse to the second point. The application should
be repainted so that you can see the line changing size and position as you
are dragging the mouse. When the mouse button is released, the line is
drawn.
As you will recognize, running this program does not create any drawing by the user. I believe this error is encountered due to line 21: g.drawLine(x, y, x2, y2); being incorrect since this is the statement defining the drawing of the line.
Any help is greatly appreciated. Thank you in advance for all your time and cooperation regarding this matter.
My code to answer the question is:
import java.awt.*;
import java.awt.event.*;
public class LineDrawer extends Canvas
implements MouseListener, MouseMotionListener {
int x, y, x2, y2;
public LineDrawer() {
super();
setSize(300, 200);
setBackground(Color.white);
}
public void mouseClicked(MouseEvent me) {
int x = me.getX();
int y = me.getY();
int x2 = me.getX();
int y2 = me.getY();
}
public void paint(Graphics g) {
g.drawLine(x, y, x2, y2);
g.setColor(Color.blue);
}
public void mousePressed(MouseEvent me) {
repaint();
}
public void mouseDragged(MouseEvent me) {
}
public void mouseExited(MouseEvent me) {
}
public void mouseEntered(MouseEvent me) {
}
public void mouseReleased(MouseEvent me) {
}
public void mouseMoved(MouseEvent me) {
}
public static void main(String args[]) {
LineDrawer ld = new LineDrawer();
GUIFrame frame = new GUIFrame("Line Drawer");
frame.add(ld);
frame.pack();
frame.setVisible(true);
}
}
P.S.: I have been hesitant to ask for help since I am concerned that other programmers would answer with methods that I have not yet learned.

int x1, y1, x2, y2;
public void mousePressed(MouseEvent e){
x1 = e.getX();
y1 = e.getY();
}
public void mouseDragged(MouseEvent e){
x2 = e.getX();
y2 = e.getY();
// Now Paint the line
repaint();
}
Hope it helps.

Let's start with
public void mouseClicked(MouseEvent me) {
int x = me.getX();
int y = me.getY();
int x2 = me.getX();
int y2 = me.getY();
}
You have previous declared x, y, x2 and y2, but in this method, you have overridden those decelerations with new ones, meaning that the previous declared variables will not be used and the event parameters will be ignored.
mouseClicked is fired AFTER a mousePressed and mouseReleased event, meaning that this is actually when the user has released the mouse button.
Extreme Coder has pointed out that MouseClicked is only fired when the mouse button is pressed and released at the same point, i.e. no dragging is involved - it's still not the right method to use, but the clarification is nice
What you should do is...
On mousePressed store the x, y position of the click and on mouseReleased store the x2, y2 position.
On the mouseDragged event, you should update the x2, y2 values and call repaint
public void mousePressed(MouseEvent me) {
// Mouse is down, but hasn't yet being released...
x = me.getX();
y = me.getY();
// We need to "override" any previous values...
x2 = x;
y2 = y;
repaint();
}
public void mouseDragged(MouseEvent me) {
x2 = me.getX();
y2 = me.getY();
repaint();
}
public void mouseReleased(MouseEvent me) {
// Here I would store the points so I could re-draw each new line...
}
Instead of using x, y, x2 and y2, it might be better to use two arrays, ie
private int[] startPoint;
private int[] endPoint;
Then you could do something like...
public void mousePressed(MouseEvent me) {
// Mouse is down, but hasn't yet being released...
startPoint = new int[2];
startPoint[0] = me.getX();
startPoint[1] = me.getY();
endPoint = startPoint;
repaint();
}
public void mouseDragged(MouseEvent me) {
endPoint = new int[2];
endPoint[0] = me.getX();
endPoint[1] = me.getY();
repaint();
}
Now I prefer paintComponent from JComponent, but I'll stick to you example for now..
public void paint(Graphics g) {
super.paint(g); // This is super important...
if (startPoint != null && endPoint != null && startPoint.length == 2 && endPoint.length == 2) {
g.drawLine(startPoint[0], startPoint[1], endPoint[0], endPoint[1]);
}
}
Additional
This is of some concern...
public void paint(Graphics g) {
g.drawLine(x, y, x2, y2);
g.setColor(Color.blue);
}
The order of operation is VERY important. Setting the color AFTER you've painted the line with have no effect on you paint operations (but may effect paint operations that occur after you).
Also, you MUST call super.paint(g) - this is super important...
Examples
A "basic" example, using int[] arrays for point storage...
public class BasicLineDraw {
public static void main(String[] args) {
new BasicLineDraw();
}
public BasicLineDraw() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (Exception ex) {
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new DrawLinePane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class DrawLinePane extends JPanel {
private int[] startPoint;
private int[] endPoint;
private List<int[][]> lines;
public DrawLinePane() {
lines = new ArrayList<int[][]>(25);
MouseAdapter handler = new MouseAdapter() {
#Override
public void mousePressed(MouseEvent e) {
startPoint = new int[]{e.getX(), e.getY()};
endPoint = startPoint;
repaint();
}
#Override
public void mouseDragged(MouseEvent e) {
endPoint = new int[]{e.getX(), e.getY()};
repaint();
}
#Override
public void mouseReleased(MouseEvent e) {
if (startPoint != null && endPoint != null && startPoint.length == 2 && endPoint.length == 2) {
lines.add(new int[][]{startPoint, endPoint});
}
startPoint = null;
endPoint = null;
repaint();
}
};
addMouseListener(handler);
addMouseMotionListener(handler);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
if (startPoint != null && endPoint != null && startPoint.length == 2 && endPoint.length == 2) {
g2d.setColor(Color.RED);
g2d.drawLine(startPoint[0], startPoint[1], endPoint[0], endPoint[1]);
}
g2d.setColor(Color.BLUE);
for (int[][] line : lines) {
g2d.drawLine(line[0][0], line[0][1], line[1][0], line[1][1]);
}
g2d.dispose();
}
}
}
And a more advanced example, using Point and Java's 2D Graphics API
public class LineDrawer {
public static void main(String[] args) {
new LineDrawer();
}
public LineDrawer() {
EventQueue.invokeLater(new Runnable() {
#Override
public void run() {
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (Exception ex) {
}
JFrame frame = new JFrame("Testing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setLayout(new BorderLayout());
frame.add(new DrawLinePane());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
});
}
public class DrawLinePane extends JPanel {
private Point anchor;
private Point lead;
private List<Line2D> lines;
public DrawLinePane() {
lines = new ArrayList<Line2D>(25);
MouseAdapter handler = new MouseAdapter() {
#Override
public void mousePressed(MouseEvent e) {
lead = null;
anchor = e.getPoint();
repaint();
}
#Override
public void mouseDragged(MouseEvent e) {
lead = e.getPoint();
repaint();
}
#Override
public void mouseReleased(MouseEvent e) {
if (lead != null && anchor != null && !anchor.equals(lead)) {
lines.add(new Line2D.Float(anchor, lead));
}
repaint();
}
};
addMouseListener(handler);
addMouseMotionListener(handler);
}
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
Graphics2D g2d = (Graphics2D) g.create();
g2d.setColor(Color.RED);
if (lead != null && anchor != null) {
Composite composite = g2d.getComposite();
g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, 0.25f));
g2d.draw(new Line2D.Float(anchor, lead));
g2d.setComposite(composite);
}
for (Line2D line : lines) {
g2d.draw(line);
}
g2d.dispose();
}
}
}