java - I need the right Pixel Per Meter Ratio implementation using JBox2D - Not Using LibGDX -

i'm building game engine , i've added jbox2d.

i'm struggling implement correct way of using ppm.

i have 3 important classes magic happens.

please review code , show me change.

this i'd see working: http://imgur.com/a/effwv

however though see that, doesn't behave accordingly.

playstate.java

package enginex.jbox2dtestbed;  import java.awt.graphics2d; import java.awt.point; import java.awt.event.mouseevent; import java.util.arraylist;  import org.jbox2d.common.vec2; import org.jbox2d.dynamics.world;  import enginex.core.state;  public class playstate extends state {     testgame                game;     boolean                 initialized = false;      vec2                        gravity         = new vec2(0.0f, 0.8f);     boolean                 dosleep         = true;     world                       world               = new world(gravity, dosleep);      arraylist<ball> balls               = new arraylist<ball>();     box                         box;      protected playstate(testgame game) {         super(game);         this.game = game;     }      public void postinit() {         if(!initialized) {             box = new box(game);              initialized = true;         }     }      public void update() {         postinit();         updateworld();         for(ball b:balls)             b.update();     }      public void updateworld() {         float timestep = 1.0f / 60.f;         int velocityiterations = 6;         int positioniterations = 2;          for(int = 0; < 60; ++i)             world.step(timestep, velocityiterations, positioniterations);     }      public void render(graphics2d g) {         for(ball b:balls)             b.render(g);          box.render(g);     }      public void mousepressed(mouseevent e) {         point m = game.getmouseposition();         try {             balls.add(new ball(game, m.x, m.y));         }         catch(exception ex) {}     } } 

ball.java

package enginex.jbox2dtestbed;  import java.awt.color; import java.awt.graphics2d;  import org.jbox2d.collision.shapes.circleshape; import org.jbox2d.dynamics.body; import org.jbox2d.dynamics.bodydef; import org.jbox2d.dynamics.bodytype; import org.jbox2d.dynamics.fixturedef;  import enginex.core.gameobject;  @suppresswarnings("serial") public class ball extends gameobject {     testgame    game;      public double   x;     public double   y;     public int      w       = 20;     public int      h       = 20;      body                    body;     bodydef             bd  = new bodydef();     circleshape     cs  = new circleshape();     fixturedef      fd  = new fixturedef();      public ball(testgame game, double x, double y) {         super(game);         this.game = game;         this.x = x - w / 2;         this.y = y - h / 2;          bd.position.set((float)this.x, (float)this.y);         bd.type = bodytype.dynamic;         cs.m_radius = w;         fd.shape = cs;         fd.density = 0.5f; // weight         fd.friction = 0.3f; // roughness         fd.restitution = 0.5f; // bounciness         body = getstate().world.createbody(bd);         body.createfixture(fd);     }      public void update() {         this.x = body.getposition().x;         this.y = body.getposition().y;     }      public void render(graphics2d g) {         g.setcolor(color.white);         g.drawoval((int)x, (int)y, (int)w, (int)h);     }      playstate getstate() {         return (playstate)game.statemachine.getcurrentstate();     } } 

box.java

package enginex.jbox2dtestbed;  import java.awt.color; import java.awt.graphics2d;  import org.jbox2d.collision.shapes.polygonshape; import org.jbox2d.dynamics.body; import org.jbox2d.dynamics.bodydef; import org.jbox2d.dynamics.bodytype; import org.jbox2d.dynamics.fixturedef;  import enginex.core.gameobject;  @suppresswarnings("serial") public class box extends gameobject {     testgame            game;      public double   x = 100;     public double   y = 100;     public int      w = 100;     public int      h = 100;      body                    body;     bodydef             bd  = new bodydef();     polygonshape    ps  = new polygonshape();     fixturedef      fd  = new fixturedef();      float                   ppm = 1/32;      public box(testgame game) {         super(game);         this.game = game;          bd.type = bodytype.static;  //      bd.position.set((float)(x), (float)(y)); //      ps.setasbox((float)(w), (float)(h));          bd.position.set((float)(x / ppm), (float)(y / ppm));         ps.setasbox((float)(w / ppm), (float)(h / ppm));          fd.shape = ps;         body = getstate().world.createbody(bd);         body.createfixture(fd);     }      public void render(graphics2d g) {         g.setcolor(color.white);         g.drawrect((int)(x), (int)(y), (int)(w), (int)(h));     }      playstate getstate() {         return (playstate)game.statemachine.getcurrentstate();     } }