How to draw in JPanel Swing graphics Java

Question

I m working on a project in which I am trying to make a paint program  So far I ve used Netbeans to create a GUI and set up the program   As of right now I am able to call all the coordinated necessary to draw inside it but I am very confused with how to actually paint inside it   Towards the end of my code I have a failed attempt at drawing inside the panel   Can anyone explain show how to use graphics in a example like this   All examples I have found make a class and extend it with JPanel but I don t know if I can do this since it was generated in netbeans   I need to draw inside a JPanel  inside my JFrame   I don t know where to put the graphics class   JavaPaintUI Class  package javapaint   import java awt    import javax swing     public class JavaPaintUI extends javax swing JFrame    public JavaPaintUI         initComponents        private void initComponents           jPanel2   new javax swing JPanel         jPanel2 setBackground new java awt Color 255  255  255        jPanel2 setBorder javax swing BorderFactory createBevelBorder javax swing border BevelBorder RAISED        jPanel2 addMouseListener new java awt event MouseAdapter             public void mousePressed java awt event MouseEvent evt                jPanel2MousePressed evt                     public void mouseReleased java awt event MouseEvent evt                jPanel2MouseReleased evt                         jPanel2 addMouseMotionListener new java awt event MouseMotionAdapter             public void mouseDragged java awt event MouseEvent evt                jPanel2MouseDragged evt                         pack         lt  editor-fold gt                           int currentX  currentY  oldX  oldY   private void jPanel2MouseDragged java awt event MouseEvent evt                                             if  tool    1            currentX   evt getX            currentY   evt getY            oldX   currentX          oldY   currentY          System out println currentX         currentY           System out println  PEN                                                      private void jPanel2MousePressed java awt event MouseEvent evt                                             oldX   evt getX        oldY   evt getY        System out println oldX         oldY                                             mouse released   private void jPanel2MouseReleased java awt event MouseEvent evt                                              if  tool    2            currentX   evt getX            currentY   evt getY            System out println  line     from    oldX    to    currentX                                                   set ui visible   public static void main String args          java awt EventQueue invokeLater new Runnable              public void run                 new JavaPaintUI   setVisible true                           Variables declaration - do not modify                      private javax swing JPanel jPanel2     End of variables declaration                     class jPanel2 extends JPanel         Override     public void paintComponent Graphics g            super paintComponent g            g drawString  BLAH   20  20           g drawRect 200  200  200  200               Screen shot  The whole thing is a JFrame and the white section in the center is jPanel2 which is what I want to draw on

User · Answer

When working with graphical user interfaces, you need to remember that drawing on a pane is done in the Java AWT/Swing event queue. You can't just use the Graphics object outside the paint()/paintComponent()/etc. methods.

However, you can use a technique called "Frame buffering". Basically, you need to have a BufferedImage and draw directly on it (see it's createGraphics() method; that graphics context you can keep and reuse for multiple operations on a same BufferedImage instance, no need to recreate it all the time, only when creating a new instance). Then, in your JPanel's paintComponent(), you simply need to draw the BufferedImage instance unto the JPanel. Using this technique, you can perform zoom, translation and rotation operations quite easily through affine transformations.

User · Answer

Here is a simple example  I suppose it will be easy to understand   import java awt    import javax swing JFrame  import javax swing JPanel   public class Graph extends JFrame   JFrame f   new JFrame    JPanel jp    public Graph         f setTitle  Simple Drawing        f setSize 300  300       f setDefaultCloseOperation EXIT ON CLOSE        jp   new GPanel        f add jp       f setVisible true      public static void main String   args        Graph g1   new Graph        g1 setVisible true      class GPanel extends JPanel       public GPanel             f setPreferredSize new Dimension 300  300                Override     public void paintComponent Graphics g              rectangle originates at 10 10 and ends at 240 240         g drawRect 10  10  240  240             filled Rectangle with rounded corners              g fillRoundRect 50  50  100  100  80  80                And the output looks like this

User · Answer

Variation of the code by Bijaya Bidari that is accepted  by Java 8 without  warnings in regard with overridable method calls in constructor   public class Graph extends JFrame       JPanel jp       public Graph             super  Simple Drawing            super setSize 300  300           super setDefaultCloseOperation EXIT ON CLOSE            jp   new GPanel            super add jp              public static void main String   args            Graph g1   new Graph            g1 setVisible true              class GPanel extends JPanel           public GPanel                 super setPreferredSize new Dimension 300  300                        Override         public void paintComponent Graphics g                super paintComponent g                 rectangle originated at 10 10 and end at 240 240             g drawRect 10  10  240  240                         filled Rectangle with rounded corners                  g fillRoundRect 50  50  100  100  80  80

User · Answer

Note the extra comments   import java awt    import java awt event    import javax swing    import javax swing border     class JavaPaintUI extends JFrame        private int tool   1      int currentX  currentY  oldX  oldY       public JavaPaintUI             initComponents               private void initComponents                we want a custom Panel2  not a generic JPanel          jPanel2   new Panel2             jPanel2 setBackground new java awt Color 255  255  255            jPanel2 setBorder BorderFactory createBevelBorder BevelBorder RAISED            jPanel2 addMouseListener new MouseAdapter                 public void mousePressed MouseEvent evt                    jPanel2MousePressed evt                             public void mouseReleased MouseEvent evt                    jPanel2MouseReleased evt                                     jPanel2 addMouseMotionListener new MouseMotionAdapter                 public void mouseDragged MouseEvent evt                    jPanel2MouseDragged evt                                         add the component to the frame to see it          this setContentPane jPanel2              be nice to testers           this setDefaultCloseOperation JFrame EXIT ON CLOSE           pack             lt  editor-fold gt       private void jPanel2MouseDragged MouseEvent evt            if  tool    1                currentX   evt getX                currentY   evt getY                oldX   currentX              oldY   currentY              System out println currentX         currentY               System out println  PEN                             private void jPanel2MousePressed MouseEvent evt            oldX   evt getX            oldY   evt getY            System out println oldX         oldY                 mouse released       private void jPanel2MouseReleased MouseEvent evt            if  tool    2                currentX   evt getX                currentY   evt getY                System out println  line     from    oldX    to    currentX                          set ui visible       public static void main String args              EventQueue invokeLater new Runnable                 public void run                     new JavaPaintUI   setVisible true                                           Variables declaration - do not modify     private JPanel jPanel2         End of variables declaration         This class name is very confusing  since it is also used as the        name of an attribute        class jPanel2 extends JPanel       class Panel2 extends JPanel            Panel2                    set a preferred size for the custom panel              setPreferredSize new Dimension 420 420                        Override         public void paintComponent Graphics g                super paintComponent g                g drawString  BLAH   20  20               g drawRect 200  200  200  200                       Screen Shot    Other examples - more tailored to multiple lines  amp  multiple line segments  HFOE put a good link as the first comment on this thread   Camickr also has a description of active painting vs  drawing to a BufferedImage in the Custom Painting Approaches article   See also this approach using painting in a BufferedImage

[java] How to draw in JPanel? (Swing/graphics Java)

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