After the repaint method is rewritten in swing, the painting will flash or fail to be updated in time.

1: The dual-buffer solution is circulated above, but this will waste the memory. If this method is used in distributed applications, the consequences will be very serious.

2: The reason is that the current drawing is not displayed when repaint is triggered.

 

 

Import java. AWT. borderlayout;

Import java. AWT. color;

Import java. AWT. graphics;

Import java. AWT. graphics2d;

Import java. AWT. Point;

Import java. AWT. event. mouseadapter;

Import java. AWT. event. mouseevent;

Import java. AWT. event. mousemotionadapter;

Import java. AWT. Geom. line2d;

Import java. util. vector;

Import javax. Swing. jframe;

Import javax. Swing. jpanel;

Class linepanel extends jpanel {

Private Static final long serialversionuid = 1l;

Private vector <line2d> lines = new vector <line2d> (); // stores all rows on the canvas.

Private line2d line = new line2d. Double ();

Private line2d cur = new line2d. Double (); // a straight line from the start point to the current cursor, temporary

Public linepanel (){

Super ();

This. setbackground (new color (255,255,255 ));

}

Public void setlines (vector <line2d> lines ){

This. Lines = lines;

}

Public void setcur (line2d cur ){

This. cur = cur;

}

@ Override

Public void paint (Graphics g ){

Super. Paint (g );

Graphics2d g2d = (graphics2d) g;

For (line2d l2d: lines) {// draw the finished graph that shows the storage

Line = l2d;

G2d. Draw (line );

}

I
F (C
Ur! = NULL) {// draw a temporary drawing. If this step is not performed, the drawing will not be smooth or flickering.

G2d. Draw (cur );

}

}

}

Public class drawline extends jframe {

Private Static final long serialversionuid = 1l;

Private linepanel panel;

Private vector <line2d> lines;

Private point start;

Public drawline (){

Panel = new linepanel ();

Lines = new vector <line2d> ();

This. setbounds (100,200,400,400 );

This. setlayout (New borderlayout ());

This. Add (panel, borderlayout. center );

This. setpanellistener ();

This. setdefaclocloseoperation (jframe. exit_on_close );

This. setvisible (true );

}

Private void setpanellistener (){

Panel. addmouselistener (New mouseadapter (){

@ Override

Public void mousepressed (mouseevent e ){

Start = new point (E. getx (), E. Gety (); // stores the starting coordinate points when you press the mouse.

}

@ Override

Public void mousereleased (mouseevent e ){

Line2d line = new line2d. Double (start. X, start. Y, E. getx (), E. Gety ());

Lines. Add (line); // stores the finished drawing because the drawing is definitely over when the mouse is released.

Panel. setlines (lines );

Line = NULL;

}

});

Panel. addmousemotionlistener (New mousemotionadapter (){

@ Override

Public void mousedragged (mouseevent e ){

Panel. setcur (New line2d. Double (start. X, start. Y, E. getx (), E. Gety ()));

// During the Drag and Drop Process, the image is excessive and cannot be stored in the vector. Otherwise, it will be a great waste of resources, so it should be processed separately.

Panel. repaint ();

}

});

}

Public static void main (string [] ARGs ){

New drawline ();

}

}