Inside the Java box ball bouncing and gravity

/**Bouncepanel.java*/Importjava.awt.*;Importjava.awt.event.*;Importjava.awt.geom.*;ImportJava.util.Random;Importjavax.swing.*; Public classBouncepanelextendsJComponentImplementsComponentlistener, Runnable {Final Static LongSerialversionuid = 0;//Kill Warning//Constants    Final StaticBasicstroke stroke =NewBasicstroke (2.0f); // Fields    intRed,green,blue; floatXsize,ysize;//Size of window    floatXpos,ypos,yypos;//position of Ball    floatXlen,ylen;//size of ball    floatSpeed//distance the ball moves on each frame    floatDx,dy,ddy,da;//Current speed + direction 's Ball    floattemp; intT; intDelay//delay between frames in milisecondsThread Animthread;//Animation Thread                    /************************************************* * Draws the ball on the screen . *************************************************/                                     Public voidpaintcomponent (Graphics g) {graphics2d g2=(graphics2d) g.create (); //get the current window sizeDimension Dim =GetSize (); Xsize=Dim.width; Ysize=Dim.height; //Clear background to WhiteG2.setpaint (Color.White); G2.fill (NewRectangle2d.double (0,0, xsize,ysize)); //Draw BallG2.setpaint (NewColor (Red,green,blue)); G2.fill (NewEllipse2d.double (xpos, ysize-ypos-Ylen, Xlen, Ylen));        G2.setcolor (Color.Black); G2.draw (NewEllipse2d.double (xpos, ysize-ypos-Ylen, Xlen, Ylen));    G2.dispose (); }        //empty methods that is required by the GUI event loop     Public voidComponenthidden (ComponentEvent e) {} Public voidcomponentmoved (ComponentEvent e) {} Public voidcomponentresized (ComponentEvent e) {} Public voidComponentshown (ComponentEvent e) {}/**************************************************** * Checks to see if the ball have hit any walls.      * Called from within run (). ****************************************************/     Public voidCheckwalls () {Random rand=NewRandom (); if(Xpos + Xlen >=xsize) {xpos= Xsize-Xlen; DX= -DX; Red=rand.nextint (256); Green=rand.nextint (256); Blue=rand.nextint (256); }        if(xpos <= 0) {xpos= 0; DX= -DX; Red=rand.nextint (256); Green=rand.nextint (256); Blue=rand.nextint (256); }        if(Ypos + Ylen >=ysize) {ypos= Ysize-Ylen; Dy= -dy; Red=rand.nextint (256); Green=rand.nextint (256); Blue=rand.nextint (256); }                    if(ypos <= 0) {ypos= 0; Dy= (float) Math.sqrt (2*da*yypos+ddy*Ddy); Red=rand.nextint (256); Green=rand.nextint (256); Blue=rand.nextint (256); }          }   /*Public void Speed () {}*/    /*********************************************************** * This is the animation thread.     * The code here's what actually causes the ball to bounce. ***********************************************************/      Public voidrun () { while(true) {//Loop Forever//Storage History Datayypos=ypos; Ddy=dy; //New VyDy=dy +da; //Update PositionXpos + =DX; Temp= (Dy+ddy)/2;//*|t=1|Ypos =ypos +temp; //check to see if the ball have hit any wallsCheckwalls (); //sleep a bit until the next frame        Try{thread.sleep (delay);} Catch(Interruptedexception e) { Break; } //Refresh the displayrepaint (); }    }            /**************************************************** * This was a constructor for the Bouncepanel class.     * It initializes all the values, the class needs * in order to work properly. ****************************************************/         PublicBouncepanel () {//set values for all the variablesXsize = 480; Ysize= 700; Xpos= 240; Ypos= 350; Xlen= 30; Ylen= 30; speed= 10; DX=Speed ; Dy=Speed ; Da= -1.0f; Delay= 80; //Set up window propertiesSetBackground (Color.White); Setopaque (true); Setpreferredsize (NewDimension ((int) Xsize, (int) (ysize)) ; Setfocusable (true); Addcomponentlistener ( This); //start the animation threadAnimthread =NewThread ( This);    Animthread.start (); }}

Inside the Java box ball bouncing and gravity