Libgdx and Box2d Detect Collision of two specific bodies -

i have 2 bodies, both dynamic, 1 of them have turned off gravity , want turn on when hit other body. know can set own contact listener want specify action if 2 specific bodies touch.

any 1 have guidance?

u can set userdata of body , use that

public class gamecoliision implements contactlistener   {  public gamecoliision() {   }  @override public void begincontact(contact contact) {     // todo auto-generated method stub     body a=contact.getfixturea().getbody();     body b=contact.getfixtureb().getbody();     a.getuserdata();     if(a.getuserdata() instanceof obstacle&&b.getuserdata() instanceof car)     {      } }  @override public void endcontact(contact contact) {     // todo auto-generated method stub  }  @override public void presolve(contact contact, manifold oldmanifold) {     // todo auto-generated method stub  }  @override public void postsolve(contact contact, contactimpulse impulse) {     // todo auto-generated method stub  }  }  public class obstacle   {  public body rectanglebody; public body trianglebody; world world; public static final float width=10/40f;  public static final float height=10/40f;    public obstacle(world world,float x,float y)  {     this.world=world;     initrectangle(x,y); }   private void initrectangle(float x, float y)  {     bodydef  bodydef=new bodydef();     fixturedef fixturedef=new fixturedef();      bodydef.type=bodytype.dynamicbody;     rectanglebody=world.createbody(bodydef);      polygonshape  polygonshape=new polygonshape();      polygonshape.setasbox(width,height);     fixturedef.shape=polygonshape;      fixturedef.friction=1f;     fixturedef.density = 1f;      rectanglebody.createfixture(fixturedef);     rectanglebody.settransform(x, y, 0) ;        rectanglebody.setangulardamping(0);      rectanglebody.setuserdata(this);  } 

hope solves problem