Drawing in Java using Canvas

Question

I want to draw in Java s Canvas but can t get it work because I don t know what I m doing   Here s my simple code   import javax swing JFrame  import java awt Canvas  import java awt Graphics  import java awt Color   public class Program       public static void main String   args                JFrame frmMain   new JFrame            frmMain setDefaultCloseOperation JFrame EXIT ON CLOSE           frmMain setSize 400  400            Canvas cnvs   new Canvas            cnvs setSize 400  400            frmMain add cnvs           frmMain setVisible true            Graphics g   cnvs getGraphics            g setColor new Color 255  0  0            g drawString  Hello   200  200             Nothing appears on the window   Am I wrong to think that Canvas is a paper and Graphics is my Pencil  Is that how it works

User · Answer

Why would the first way not work  Canvas object is created and the size is set and the grahpics are set  I always find this strange  Also if a class extends JComponent you can override the   paintComponent      super        and then shouldn t you be able to create and instance of the class inside of another class and then just call  NewlycreateinstanceOfAnyClass repaint     I have tried this approach for some game programming I have been working and it doesn t seem to work the way I think that it should be   Doug Hauf

User · Answer

You ve got to override your Canvas s paint Graphics g  method and perform your drawing there  See the paint   documentation   As it states  the default operation is to clear the canvas  so your call to the canvas  graphics object doesn t perform as you would expect

User · Answer

The following should work   public static void main String   args        final String title    Test Window       final int width   1200      final int height   width   16   9         Creating the frame      JFrame frame   new JFrame title        frame setSize width  height       frame setDefaultCloseOperation JFrame EXIT ON CLOSE       frame setLocationRelativeTo null       frame setResizable false       frame setVisible true          Creating the canvas      Canvas canvas   new Canvas         canvas setSize width  height       canvas setBackground Color BLACK       canvas setVisible true       canvas setFocusable false           Putting it all together      frame add canvas        canvas createBufferStrategy 3        boolean running   true       BufferStrategy bufferStrategy      Graphics graphics       while  running            bufferStrategy   canvas getBufferStrategy            graphics   bufferStrategy getDrawGraphics            graphics clearRect 0  0  width  height            graphics setColor Color GREEN           graphics drawString  This is some text placed in the top left corner    5  15            bufferStrategy show            graphics dispose

User · Answer

Suggestions    Don t use Canvas as you shouldn t mix AWT with Swing components unnecessarily   Instead use a JPanel or JComponent  Don t get your Graphics object by calling getGraphics   on a component as the Graphics object obtained will be transient  Draw in the JPanel s paintComponent   method  All this is well explained in several tutorials that are easily found  Why not read them first before trying to guess at this stuff      Key tutorial links    Basic Tutorial  Lesson  Performing Custom Painting More advanced information  Painting in AWT and Swing

[java] Drawing in Java using Canvas

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