How to draw lines in Java

Question

I m wondering if there s a funciton in Java that can draw a line from the coordinates  x1  x2  to  y1  y2    What I want is to do something like this   drawLine x1  x2  x3  x4     And I want to be able to do it at any time in the code  making several lines appear at once   I have tried to do this   public void paint Graphics g      g drawLine 0  0  100  100       But this gives me no control of when the function is used and I can t figure out how to call it several times   Hope you understand what I mean   P S  I want to create a coordinate system with many coordinates

User · Answer

I understand you are using Java AWT API for drawing. The paint method is invoked when the control needs repainting. And I'm pretty sure it provides in the Graphics argument what rectangle is the one who needs repainting (to avoid redrawing all).

So if you are presenting a fixed image you just draw whatever you need in that method.

If you are animating I assume you can invalidate some region and the paint method will be invoked automagically. So you can modify state, call invalidate, and it will be called again.

User · Answer

You need to create a class that extends Component  There you can override the paint method and put your painting code in   package blah whatever   import java awt Component  import java awt Graphics   public class TestAWT extends Component         see java awt Component paint java awt Graphics      Override public void paint Graphics g        super paint g       g drawLine 0 0 100 100       g drawLine 10  10  20  300          more drawing code here           Put this component into the GUI of your application  If you re using Swing  you need to extend JComponent and override paintComponent  instead   As Helios mentioned  the painting code actually tells the system how your component looks like  The system will ask for this information  call your painting code  when it thinks it needs to be  re painted  for example  if a window is moved in front of your component

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I built a whole class of methods to draw points  lines  rectangles  circles  etc  I designed it to treat the window as a piece of graph paper where the origin doesn t have to be at the top left and the y values increase as you go up  Here s how I draw lines   public static void drawLine  double x1  double y1  double x2  double y2                 Graphics2D g  draw new Line2D Double x0 x1 scale  y0-y1 scale  x0 x2 scale  y0-y2 scale        In the example above   x0  y0  represents the origin in screen coordinates and scale is a scaling factor  The input parameters are to be supplied as graph coordinates  not screen coordinates  There is no repaint   being called  You can save that til you ve drawn all the lines you need   It occurs to me that someone might not want to think in terms of graph paper         Graphics2D g  draw new Line2D Double x1  y1  x2  y2      Notice the use of Graphics2D  This allows us to draw a Line2D object using doubles instead of ints  Besides other shapes  my class has support for 3D perspective drawing and several convenience methods  like drawing a circle centered at a certain point given a radius   If anyone is interested  I would be happy to share more of this class

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To give you some idea   public void paint Graphics g       drawCoordinates g      private void drawCoordinates Graphics g          get width  amp  height here  w h        define grid width  dh  dv     for  int x   0  i  lt  w  i    dh        g drawLine x  0  x  h         for  int y   0  j  lt  h  j    dv          g drawLine 0  y  w  y

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a simple line   after that you can see also a doted line   import java awt     import javax swing     import java awt Graphics     import java awt Graphics2D     import javax swing JFrame   import javax swing JPanel   import java awt BasicStroke   import java awt Event     import java awt Component     import javax swing SwingUtilities               author junaid     public class JunaidLine extends JPanel      private Graphics Graphics   private void doDrawing Graphics g    Graphics2D g2d  Graphics2D  g   float   dash1    2f 0f 2f    g2d drawLine 20  40  250  40    BasicStroke bs1   new BasicStroke 1 BasicStroke CAP BUTT                       BasicStroke JOIN ROUND 1 0f dash1 2f    g2d setStroke bs1    g2d drawLine 20  80  250  80            Override  public void paintComponent Graphics g    super paintComponent  g    doDrawing g           class BasicStrokes extends JFrame   public  BasicStrokes     initUI        private void initUI     setTitle  line     setDefaultCloseOperation JFrame DISPOSE ON CLOSE    add new JunaidLine      setSize 280 270    setLocationRelativeTo null               param args the command line arguments      public static void main String   args      SwingUtilities invokeLater new Runnable         Override  public void run     BasicStrokes bs   new BasicStrokes     bs setVisible true

User · Answer

To answer your original question  it s  x1  y1  to  x2  y2    For example    This is to draw a horizontal line   g drawLine  10  30  90  30      vs  This is to draw a vertical line   g drawLine  10  30  10  90      I hope it helps

User · Answer

In your class you should have   public void paint Graphics g      g drawLine x1  y1  x2  y2       Then in code if there is needed you will change x1  y1  x2  y2 and call repaint

User · Answer

You can use the getGraphics method of the component on which you would like to draw  This in turn should allow you to draw lines and make other things which are available through the Graphics class

User · Answer

A very simple example of a swing component to draw lines  It keeps internally a list with the lines that have been added with the method addLine  Each time a new line is added  repaint is invoked to inform the graphical subsytem that a new paint is required   The class also includes some example of usage   import java awt BorderLayout  import java awt Color  import java awt Dimension  import java awt Graphics  import java awt event ActionEvent  import java awt event ActionListener  import java util LinkedList   import javax swing JButton  import javax swing JComponent  import javax swing JFrame  import javax swing JPanel   public class LinesComponent extends JComponent   private static class Line      final int x1       final int y1      final int x2      final int y2         final Color color       public Line int x1  int y1  int x2  int y2  Color color            this x1   x1          this y1   y1          this x2   x2          this y2   y2          this color   color                          private final LinkedList lt Line gt  lines   new LinkedList lt Line gt      public void addLine int x1  int x2  int x3  int x4        addLine x1  x2  x3  x4  Color black      public void addLine int x1  int x2  int x3  int x4  Color color        lines add new Line x1 x2 x3 x4  color                repaint       public void clearLines         lines clear        repaint        Override protected void paintComponent Graphics g        super paintComponent g       for  Line line   lines            g setColor line color           g drawLine line x1  line y1  line x2  line y2            public static void main String   args        JFrame testFrame   new JFrame        testFrame setDefaultCloseOperation JFrame DISPOSE ON CLOSE       final LinesComponent comp   new LinesComponent        comp setPreferredSize new Dimension 320  200        testFrame getContentPane   add comp  BorderLayout CENTER       JPanel buttonsPanel   new JPanel        JButton newLineButton   new JButton  New Line        JButton clearButton   new JButton  Clear        buttonsPanel add newLineButton       buttonsPanel add clearButton       testFrame getContentPane   add buttonsPanel  BorderLayout SOUTH       newLineButton addActionListener new ActionListener               Override         public void actionPerformed ActionEvent e                int x1    int   Math random   320               int x2    int   Math random   320               int y1    int   Math random   200               int y2    int   Math random   200               Color randomColor   new Color  float Math random     float Math random     float Math random                 comp addLine x1  y1  x2  y2  randomColor                         clearButton addActionListener new ActionListener               Override         public void actionPerformed ActionEvent e                comp clearLines                          testFrame pack        testFrame setVisible true

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Store the lines in some type of list   When it comes time to paint them  iterate the list and draw each one   Like this  Screenshot  DrawLines import java awt Color  import java awt Dimension  import java awt Graphics  import java awt geom Line2D   import javax swing JOptionPane  import javax swing JComponent  import javax swing SwingUtilities   import java util ArrayList  import java util Random   class DrawLines        public static void main String   args             Runnable r   new Runnable                 public void run                     LineComponent lineComponent   new LineComponent 400 400                   for  int ii 0  ii lt 30  ii                          lineComponent addLine                                      JOptionPane showMessageDialog null  lineComponent                                    SwingUtilities invokeLater r            class LineComponent extends JComponent        ArrayList lt Line2D Double gt  lines      Random random       LineComponent int width  int height            super            setPreferredSize new Dimension width height            lines   new ArrayList lt Line2D Double gt             random   new Random               public void addLine             int width    int getPreferredSize   getWidth            int height    int getPreferredSize   getHeight            Line2D Double line   new Line2D Double              random nextInt width               random nextInt height               random nextInt width               random nextInt height                         lines add line           repaint               public void paintComponent Graphics g            super paintComponent g           g setColor Color white           g fillRect 0  0  getWidth    getHeight             Dimension d   getPreferredSize            g setColor Color black           for  Line2D Double line   lines                g drawLine                   int line getX1                     int line getY1                     int line getX2                     int line getY2

[java] How to draw lines in Java

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