Develop Reference

How to change color in a basic Paint program using java .awt

so im working on this simple painting program that records mouse events such as entering exiting, dragging,etc... the program records all these points and stores it in an array list of "lines"( A class i defined for this task) then the program paints the list to the screen. my question is how should i go about changing the color of the stuff im painting with out changing the color of the ones i have already painted any help is appreciated thank you.
import java.awt.*;
import java.awt.event.*;
import java.util.*;
public class MyNewDrawFrame extends Frame{
public MyNewDrawFrame(){
setSize(500,500);
setTitle("Drawing is fun");
addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent we){
System.exit(0);
}
});
MyNewDrawPanel mdp = new MyNewDrawPanel();
add(mdp);
setVisible(true);
}
public static void main(String[] args){
MyNewDrawFrame mdf = new MyNewDrawFrame();
}
}
class MyNewDrawPanel extends DoubleBuffer implements MouseListener, MouseMotionListener,ActionListener{
int lastX=0, lastY=0;
ArrayList<Line>lines;
Color color;
Button red, green, black, blue;
public MyNewDrawPanel() {
setLayout(new BorderLayout());
red = new Button("Red");
green = new Button("Green");
blue = new Button("Blue");
black = new Button("Black");
red.addActionListener(this);
green.addActionListener(this);
blue.addActionListener(this);
black.addActionListener(this);
red.setBackground(Color.red);
green.setBackground(Color.green);
blue.setBackground(Color.blue);
black.setBackground(Color.black);
Panel p = new Panel();
p.add(red);
p.add(green);
p.add(blue);
p.add(black);
add(p, BorderLayout.SOUTH);
lines = new ArrayList<Line>();
setBackground(Color.white);
color = Color.black;
setForeground(color);
addMouseListener(this);
addMouseMotionListener(this);
}
public Color getColor(){
return color;
}
public void setColor(Color color){
this.color = color;
}
public void mouseExited(MouseEvent me){}
public void mouseClicked(MouseEvent me){}
public void mouseReleased(MouseEvent me){
}
public void mouseEntered(MouseEvent me){
record(me.getX(), me.getY());
}
public void mousePressed(MouseEvent me){
record(me.getX(), me.getY());
}
public void mouseMoved(MouseEvent me){}
public void mouseDragged(MouseEvent me){
int x = me.getX();
int y = me.getY();
lines.add(new Line(lastX, lastY, x, y));
record(x, y);
repaint();
}
public void paint(Graphics g){
for(Line line: lines){
g.setColor(color);
g.drawLine(line.getStartX(), line.getStartY(), line.getEndX(), line.getEndY());
}
}
public void record(int x, int y) {
lastX = x;
lastY = y;
}
public void actionPerformed(ActionEvent ae){
if (ae.getSource() == red){
setColor(Color.red);
}
else if (ae.getSource() == blue){
setColor(Color.blue);
}
else if (ae.getSource() == green){
setColor(Color.green);
}
else if (ae.getSource() == black){
setColor(Color.black);
}
}
}
class Line{
int startx, starty, endx, endy;
public Line(){}
public Line(int startx, int starty, int endx, int endy){
setStartX(startx);
setStartY(starty);
setEndX(endx);
setEndY(endy);
}
public void setStartX(int startx){
this.startx = startx;
}
public void setStartY(int starty){
this.starty = starty;
}
public void setEndX(int endx){
this.endx = endx;
}
public void setEndY(int endy){
this.endy = endy;
}
public int getStartX(){
return startx;
}
public int getStartY(){
return starty;
}
public int getEndX(){
return endx;
}
public int getEndY(){
return endy;
}
}
import java.awt.*;
public class DoubleBuffer extends Panel{
private int bufferWidth;
private int bufferHeight;
private Image bufferImage;
private Graphics bufferGraphics;
public DoubleBuffer(){
super();
}
public void update(Graphics g){
paintBuffer(g);
}
public void paintBuffer(Graphics g){
// checks the buffersize with the current panelsize
// or initialises the image with the first paint
if(bufferWidth!=getSize().width || bufferHeight!=getSize().height ||bufferImage==null || bufferGraphics==null)
resetBuffer();
if(bufferGraphics!=null){
//this clears the offscreen image, not the onscreen one
bufferGraphics.clearRect(0,0,bufferWidth,bufferHeight);
//calls the paintbuffer method with
//the offscreen graphics as a param
paint(bufferGraphics);
//we finaly paint the offscreen image onto the onscreen image
g.drawImage(bufferImage,0,0,this);
}
}
public void paint(Graphics g){
//in classes extended from this one, add something to paint here!
//always remember, g is the offscreen graphics
}
private void resetBuffer(){
// always keep track of the image size
bufferWidth=getSize().width;
bufferHeight=getSize().height;
// clean up the previous image
if(bufferGraphics!=null){
bufferGraphics.dispose();
bufferGraphics=null;
}
if(bufferImage!=null){
bufferImage.flush();
bufferImage=null;
}
System.gc();
// create the new image with the size of the panel
bufferImage=createImage(bufferWidth,bufferHeight);
bufferGraphics=bufferImage.getGraphics();
}
}

Your Line class should store color. Fill it in mouseDragged and use like this
public void paint(Graphics g){
for(Line line: lines){
g.setColor(line.getColor());
g.drawLine(line.getStartX(), line.getStartY(), line.getEndX(), line.getEndY());
}
}

can't draw on a JPanel after repaint method

I'm experimenting on a GUI that I programmed and I don't understand how I can fix my problem:
My GUI contains a jPanel that on receiving a mouseclick, paints a point with filloval command.
private void myPnlMousePressed(java.awt.event.MouseEvent evt) {
changed = true;
p.x = evt.getX();
p.y = evt.getY();
drewPoints(p.x, p.y);
}
private void drewPoints (int x, int y) {
if (gf == null) {
gf = (Graphics)myPnl.getGraphics();
}
myPointsList.add(new Point(x, y));
gf.fillOval(x, y, 5, 5);
xVal.setText("X = " + x);
yVal.setText("Y = " + y);
}
everything works fine but when I want to open an XML file that I created to save all the points it doesn't work.
The problem is that when I use the repaint method on the jPanel after choosing a file, all the points loads fine but the panel can't draw the points.
If I put the repaint method in the open button listener (before the choosing file) it works, but then if the user cancels the open option so the panel stays blank and I don't want to draw the points again.
I think it happens because the repaint process is not finished.
All the points added to a private List.
private void OpenFile() {
try {
File thisFile;
JFileChooser of = new JFileChooser();
int option = of.showOpenDialog(of);
if (option == JFileChooser.APPROVE_OPTION){
thisFileName = of.getSelectedFile().getPath();
thisFile = new File(thisFileName);
if (!of.getSelectedFile().getName().endsWith(".xml")) {
String error = "Error, You didn't select XML file";
JOptionPane.showMessageDialog(this, error, "Wrong type of file", JOptionPane.INFORMATION_MESSAGE);
return;
}
myPnl.repaint();
myPointsList.clear();
....
....
....
for (int i = 0; i < pointsList.getLength(); i++) {
Element point = (Element) pointsList.item(i);
p.x = Integer.parseInt(point.getElementsByTagName("X").item(0).getTextContent());
p.y = Integer.parseInt(point.getElementsByTagName("Y").item(0).getTextContent());
drewPoints(p.x, p.y);
}
....
how can I make it work??

Don't use gf = (Graphics)myPnl.getGraphics();, this is not how painting in Swing works. The getGraphics method can return null and is nothing more then a snap shot of the last paint cycle, any thing you paint to it will be erased on the next paint cycle (repaint).
Instead, override the JPanels paintComponent and put all you painting logic there. There is an expectation that when called, you are expected to fully re-paint the current state of the component.
See Painting in AWT and Swing and Performing Custom Painting for more details about how painting works in Swing

You have to use the repaint() and override the paint() method:
class MyPanel extends JPanel implements MouseListener
{
private int x;
private int y;
public MyPanel() {
super();
addMouseListener(this);
}
#Override public void mouseEntered(MouseEvent e) { }
#Override public void mouseExited(MouseEvent e) { }
#Override public void mouseClicked(MouseEvent e) { }
#Override public void mousePressed(MouseEvent e) { }
#Override public void mouseReleased(MouseEvent e) {
x = e.getX();
y = e.getY();
repaint();
}
#Override public void paint(Graphics g) {
super.paint(g);
g.fillOval(x, y, 10, 10);
}
}
If you want to draw all points, don't use x and y but a list of points:
class MyPanel extends JPanel implements MouseListener
{
private ArrayList<Point> points = new ArrayList<>();
public MyPanel() {
super();
addMouseListener(this);
}
#Override public void mouseEntered(MouseEvent e) { }
#Override public void mouseExited(MouseEvent e) { }
#Override public void mouseClicked(MouseEvent e) { }
#Override public void mousePressed(MouseEvent e) { }
#Override public void mouseReleased(MouseEvent e) {
points.add(new Point(e.getX(), e.getY()));
repaint();
}
#Override public void paint(Graphics g) {
super.paint(g);
for (Point p : points)
g.fillOval(p.getX(), p.getY(), 10, 10);
}
}
where:
class Point
{
private int x;
private int y;
public Point(int x, int y) {
this.x = x;
this.y = y;
}
public int getX() {
return x;
}
public int getY() {
return y;
}
}
Then use it:
public static void main(String[] args) {
JFrame frame = new JFrame("Test");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(400, 400);
frame.setLocationRelativeTo(null);
MyPanel myPanel = new MyPanel();
frame.add(myPanel);
frame.setVisible(true);
}

Java mouseListener's mousemove not working

I am trying to make a plotting program, the program should show the point the user is currently on, i tried using mousemove for this function (using console for now to view result) but it's not working.
public class drawArea extends JPanel implements MouseListener {
Image img;
int w=580;
int h=580;
String equation = "";
int clicks = 0;
public drawArea(){
init();
this.addMouseListener(this);
}
private void init(){
setPreferredSize( new Dimension( w, h ) );
setVisible(true);
img = new ImageIcon("assets/Graph.png").getImage();
}
private void initializeGrid(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
g2d.drawImage(img, 0, 0, this);
}
private void drawFunction(Graphics g, String function) {
Graphics2D g2d = (Graphics2D) g;
g2d.setColor(Color.blue);
double p=0.01; //plotting precision
for(double x=-5;x<5;x+=p){
int drawingX1=gx((x));
int drawingY1=gy(f(x));
int drawingX2=gx(x+p);
int drawingY2=gy(f(x+p));
g2d.drawLine(drawingX1, drawingY1, drawingX2, drawingY2);
}
}
private double f(double x){
return x*x;
}
private int gx(double x){
return (int) ((x+5)*(w/10));
}
private int gy(double y){
return (int) (h-(y+5)*(h/10));
}
public void setEquation(String equ){
equation=equ;
}
public void paintComponent(Graphics g) {
super.paintComponent(g);
initializeGrid(g);
drawFunction(g,"Function");
}
public void mouseClicked(MouseEvent e) {
if(clicks<3){
MainUI.points[clicks][0] = e.getX();
MainUI.points[clicks][1] = e.getY();
System.out.println(e.getX()+","+e.getY());
System.out.println(MainUI.points[clicks] [0]+","+MainUI.points[clicks][1]);
clicks++;
}
}
public void mouseEntered(MouseEvent e) {
//not needed
}
public void mouseExited(MouseEvent arg0) {
//not needed
}
public void mousePressed(MouseEvent arg0) {
//not needed
}
public void mouseReleased(MouseEvent arg0) {
//not needed
}
public void mouseMoved(MouseEvent e) {
System.out.println(e.getX()+","+e.getY());
}
}
Thanks in Advance

MouseListener does not have a mouseMoved method.
You have to add the declaration that you are going to also implement the Mouse Motion Listener interface:
public class drawArea extends JPanel
implements MouseListener, MouseMotionListener
Additionally, you have to add this mouse motion listener in the constructor
this.addMouseMotionListener(this);

how to draw multiple rectangles

so I am trying to make a simple program where you click on the screen and it creates a block that falls and collides with a larger block beneath and sticks to it. Kind of like a simple collision program. The problem is when I create one block it deletes the block previously. I made an array, but it still does this. Do any of you know what Im doing wrong? Im sure its a simple fix.
public class Screen extends JPanel implements Runnable {
public static JLabel statusbar; //displays a status bar showing what mouse movements are taking place
private Image cat; //image of the cat
public int xCoord ; //get the coordinates of the mouse pressed
public int yCoord ;
public int xCreate;
public int yCreate;
public Rectangle Ground;
public Rectangle Block;
public boolean isClicked = false;
public int clickCount = 0;
Rectangle blocks[] = new Rectangle[10];
int blocknum = 0;
public Screen(Frame frame) {
loadPic(); //calls the loadPic method above
Handlerclass handler = new Handlerclass(); //creates a new class to use the mouse motion listener
System.out.println("mouse works!");
addMouseListener(handler);
addMouseMotionListener(handler);
statusbar = new JLabel("default");
add(statusbar);
}
public void run(){ //this is the game run loop
System.out.println("this is running");
try{
} catch(Exception e) {} //exception handling
}
public void loadPic(){ //loads the picture from the other project but its the same pic
cat = new ImageIcon("C:\\Users\\Camtronius\\Documents\\NetBeansProjects\\Moving Block Proj\\src\\MovingBlock\\catIcon1.png").getImage(); //gets the image
System.out.println("Image Loaded!");
}
#Override public void paintComponent(Graphics g){
super.paintComponent(g); //paints the component, the picture, on top
Graphics2D g2d = (Graphics2D) g.create();
g2d.drawImage(cat, xCoord, yCoord, null);
g2d.setColor(Color.BLUE);
Ground = new Rectangle(0,450,550,50);
g2d.fillRect(0,450, 550, 50);
for(Rectangle blocknum : blocks){
if (blocks != null) {
g2d.setColor(Color.RED);
g2d.fillRect(xCreate,yCreate,50,50);
System.out.println(blocknum);
}
}
//move();
}
public void move(){
if(yCreate<400){
yCreate+=1;
}else{
}
if(Ground.intersects(blocks[blocknum])){
yCreate=400;
System.out.println("contains!");
}
}
private class Handlerclass implements MouseListener, MouseMotionListener{
public void mouseClicked(MouseEvent event){
}
public void mousePressed(MouseEvent event){
}
public void mouseReleased(MouseEvent event){
if(blocknum<blocks.length){
xCreate=event.getX();
yCreate=event.getY();
blocks[blocknum] = new Rectangle(50,50, xCreate, yCreate);
repaint();
}
blocknum=blocknum+1;
}
public void mouseEntered(MouseEvent event){
}
public void mouseExited(MouseEvent event){
}
public void mouseDragged(MouseEvent event){
}
public void mouseMoved(MouseEvent event){
statusbar.setText(String.format("Coordinates are: %d, %d", event.getX(),event.getY()));
xCoord=event.getX();
yCoord=event.getY();
}
}
}

Painting is a destructive process. That is, when a new paint cycle runs, the previous contents of the Graphics context should be cleared...
So, in you paintComponent method you are only painting the last block...
if(isClicked = true){
blocks[blocknum] = new Rectangle(50,50, xCreate, yCreate);
g2d.setColor(Color.RED);
g2d.fillRect(xCreate,yCreate,50,50);
System.out.println(blocknum);
repaint(); // THIS IS A BAD IDEA
}
DO NOT call any method that might cause repaint to be called. This will put you in a potential cycle of death that will consume your CPU.
Instead, you should loop through the blocks array and paint each one...
for (Rectangle block : blocks) {
if (block != null) {
g2d.setColor(Color.RED);
g2d.fill(block);
}
}
And in you mouseReleased method, you should be adding the new rectangles...
public void mouseReleased(MouseEvent event){
blocknum=blocknum+1;
if (blocknum < blocks.length) {
xCreate=event.getX();
yCreate=event.getY();
blocks[blocknum] = new Rectangle(xCreate, yCreate, 50, 50);
}
}
I'd suggest you take a look at Custom Painting, Painting in AWT and Swing and Concurrency in Swing for more details

Free line drawing java2d app connects lines of each new drawing

I'm building an app that recognises lines drawn with mouse and creates music. I'm new to java2d so heres the problem i'm having:
When you draw, and then make another drawing, the last point of the previous drawing connects to the first of the new one. I havent been able to figure out how to fix this. Below is the code.
Another question is: I would like to store each stroke of drawing (from mousePressed to mouseReleased) into a ArrayList of type Shape, how can I go into that?
I'd like to be pointed in the right direction as I havent been able to find helpful info online. Thanks!
public class DrawBoard extends JPanel implements MouseListener,
MouseMotionListener {
public JLabel status;
public Point pstart, pfinish;
private Shape currentShape = null;
private ArrayList<Point> points = new ArrayList<Point>();
private ArrayList<Shape> lines = new ArrayList<Shape>();
public DrawBoard() {
Dimension size = getPreferredSize();
size.setSize(1024, 800); // w, h
setPreferredSize(size);
setOpaque(false);
status = new JLabel("default");
add(status, BorderLayout.SOUTH);
addMouseListener(this);
addMouseMotionListener(this);
}
#Override
public void mouseClicked(MouseEvent e) {
status.setText(String.format("Clicked at %d,%d", e.getX(), e.getY()));
}
// Where the drawing happens
#Override
public void mousePressed(MouseEvent e) {
status.setText("you pressed down the mouse");
this.pstart = e.getPoint();
}
#Override
public void mouseDragged(MouseEvent e) {
status.setText("you draged the mouse");
points.add(e.getPoint());
repaint();
}
#Override
public void mouseReleased(MouseEvent e) {
status.setText("you release the mouse click");
pfinish = e.getPoint();
}
// End of where the drawing happens
#Override
public void mouseEntered(MouseEvent e) {
status.setText("you entered the area");
}
#Override
public void mouseExited(MouseEvent e) {
status.setText("mouse exited the area");
}
#Override
public void mouseMoved(MouseEvent e) {
// throw new UnsupportedOperationException("Not supported yet.");
}
public void paint(Graphics g) {
super.paint(g);
Graphics2D g2 = (Graphics2D) g;
g2.setColor(Color.BLACK);
g2.setStroke(new BasicStroke(5));
for (int i = 0; i < points.size() - 2; i++) {
Point p1 = points.get(i);
Point p2 = points.get(i + 1);
g2.drawLine(p1.x, p1.y, p2.x, p2.y);
}
}
}
I have modified it using BufferedImage and it works for drawing normally, now the only thing does nto work is the clear method, i have tried different methods but none have worked. My new code is Below:
public class DrawBoard extends JPanel implements MouseListener, MouseMotionListener{
public JLabel status;
private JLabel imgLabel;
public Point pstart, pfinish;
private Shape currentShape = null;
private List<Point> points = new ArrayList<Point>();
private List<BufferedImage> lines = new ArrayList<BufferedImage>();
private static final int BI_WIDTH = 1024;
private static final int BI_HEIGHT = 800;
private BufferedImage bImage = new BufferedImage(BI_WIDTH, BI_HEIGHT,
BufferedImage.TYPE_INT_ARGB);
public DrawBoard(){
Graphics2D g2d = bImage.createGraphics();
g2d.dispose();
Dimension size = getPreferredSize();
size.setSize(1024,800); //w, h
setPreferredSize(size);
status = new JLabel("default");
add(status, BorderLayout.SOUTH);
addMouseListener(this);
addMouseMotionListener(this);
imgLabel = new JLabel(new ImageIcon(bImage)) {
#Override
protected void paintComponent(Graphics g) {
super.paintComponent(g);
paintInLabel(g);
}
};
imgLabel.setOpaque(false);
setOpaque(false);
add(imgLabel, BorderLayout.CENTER);
}
private void paintInLabel(Graphics g) {
Graphics2D g2d = (Graphics2D) g;
g2d.setColor(Color.BLUE); // this colour is when mouse is pressed
g2d.setStroke(new BasicStroke(5));
if (points.size() < 2) {
return;
}
for (int i = 1; i < points.size(); i++) {
int x1 = points.get(i - 1).x;
int y1 = points.get(i - 1).y;
int x2 = points.get(i).x;
int y2 = points.get(i).y;
g2d.drawLine(x1, y1, x2, y2);
}
}
#Override
public void mouseClicked(MouseEvent e) {
status.setText(String.format("Clicked at %d,%d", e.getX(), e.getY()));
}
// Where the drawing happens
#Override
public void mousePressed(MouseEvent e) {
status.setText("you pressed down the mouse");
this.pstart = e.getPoint();
points.add(e.getPoint());
}
#Override
public void mouseDragged(MouseEvent e) {
status.setText("you draged the mouse");
points.add(e.getPoint());
imgLabel.repaint();
}
#Override
public void mouseReleased(MouseEvent e) {
status.setText("you release the mouse click");
Graphics2D g2d = bImage.createGraphics();
g2d.setColor(Color.blue); // this is the final colour
g2d.setStroke(new BasicStroke(5));
if (points.size() >= 2) {
for (int i = 1; i < points.size(); i++) {
int x1 = points.get(i - 1).x;
int y1 = points.get(i - 1).y;
int x2 = points.get(i).x;
int y2 = points.get(i).y;
g2d.drawLine(x1, y1, x2, y2);
}
}
g2d.dispose();
points.clear();
imgLabel.repaint();
}
// End of where the drawing happens
#Override
public void mouseEntered(MouseEvent e) {
status.setText("you entered the area");
}
#Override
public void mouseExited(MouseEvent e) {
status.setText("mouse exited the area");
}
#Override
public void mouseMoved(MouseEvent e) {
//throw new UnsupportedOperationException("Not supported yet.");
}
public void clearDrawBoard() {
imgLabel.setIcon(null);
}
}

A few solutions and suggestions:
Don't draw from a single List<Point> as there's no way of knowing where one line ends and another begins.
Consider drawing each line to a BufferedImage once it is complete and display that BufferedImage in your JComponent in its paintComponent method. You would place it in the BufferedImage in the mouseReleased(...) method.
Or consider creating an List<List<Point>> so you can iterate through each line as needed. You would add the new List<Point> to the original List in the mouseReleased(...) method.
Consider using your List<Shape> and fill it with Line2D objects that can be drawn. The Line2D would be added to the List<Shape> in the mouseReleased(...) method.
Also: You should not override paint(...) but rather `paintComponent(...).
Also: Don't forget the #Override annotation for safer coding.
For example, please see my code and answer here.