java - A new object seems to change the fields of previous objects -

i'm writing game contains elevators obstacle. elevator spawns either left or right of screen , has random chance ascending elevator or descending elevator. looks this:

public class elevator extends worldobject {      public static boolean ascending;      public elevator(int screenheight, int xpos) {         super(xpos, screenheight, 0, 0);         ascending = new random().nextboolean();     }      static public boolean isascending(){         return ascending;     }  } 

worldobject extends looks this:

public class worldobject {      protected float posx;     protected float posy;     protected float velx, vely;      public float getposx() {         return posx;     }      public void setposx(float posx) {         this.posx = posx;     }      public float getposy() {         return posy;     }      public void setposy(float posy) {         this.posy = posy;     }      public float getvelx() {         return velx;     }      public void setvelx(float velx) {         this.velx = velx;     }      public float getvely() {         return vely;     }      public void setvely(float vely) {         this.vely = vely;     }      public worldobject(float posx, float posy, float velx, float vely) {         this.posx = posx;         this.posy = posy;         this.velx = velx;         this.vely = vely;     }  } 

every 5 seconds elevator created , added arraylist of elevators so:

    if (timetoelevator > 5.0f) {         timetoelevator = 0;         elevator elevator = new elevator((int) screenheight, (int) generateelevatorxpos());         sprite esprite = new sprite(elevatortexture);         esprite.setorigin(0, 0);         elevators.add(elevator);         elevatorsprites.add(esprite);     } 

i check collisions in each elevator player, remove if goes out of bounds , if neither of these happen update position of elevator object:

public static void calculateelevatorcollisions() {     int counter = 0;     (iterator<elevator> = elevators.iterator(); i.hasnext(); ) {         elevator item = i.next();         if (item.getposy() < -100) {             //remove elevator         } else if (..collision..) {             //collision         } else {             item.setvely(item.isascending() ? -5 : 5);             item.setposy(item.getvely() + item.getposy());             elevatorsprites.get(counter).setposition(item.getposx(),                     item.getposy());             counter++;         } 

my issue whenever new elevator created current elevators change direction direction of new elevator. suppose have 2 ascending elevators being drawn, whenever third elevator created descending, other 2 ascending elevators ascend!

what's causing this?

this problem:

public static boolean ascending;        ^^^^^^ 

static means "this class field shared objects". if changed field 1 object, noticed across all objects of type.

removing make ascending instance field means each instance of elevator have own copy can modify without changing other instances' copy.