TimeBalls

This is the code i have now for the balls. I use secs.format(s.getElapsedTime()/1000.000 to count the elapsed time while game ran. How to make it that enemy 2 will start after elapsed time 4s?



       Enemy1 enemy1 = new Enemy1();
         e1 = new Thread(enemy1);
         e1.start();

         Enemy2 enemy2 = new Enemy2();
         e2 = new Thread(enemy2);
         e2.start();


        }
 class Enemy1 implements Runnable{
       //each enemey runs in its own thread
       public void run(){
          while(true){
            if(avoid.getRun()){
           //move object randomly
           x2 = x2+generator.nextInt(7);
           y2 = y2+generator.nextInt(7);
           if(x2>500 || y2>500){
               int side = generator.nextInt(2);
               //which side should the ball appear on
               if(side==0)
               {x2=0;
                y2=generator.nextInt(470);}
               if(side==1)
               {x2=generator.nextInt(470);
                y2=0;}}
             x1 = avoid.getx1();
             y1 = avoid.gety1();
            if ((x1+ 30>x2 && x1-30<x2)&&(y1+ 30>y2 && y1-30<y2))
              { //calculate intersection for game over
                GameOver();
               } //draw the moved object
             avoid.set2(x2,y2);
           avoid.drawSurface.repaint();}
           try{
        //wait 10 milliseconds
           Thread.sleep(10);}
           catch(InterruptedException e) {
              System.out.println("Interrupt Caught");
      }}}}

    class Enemy2 implements Runnable{

       public void run(){
          while(true){
              if(avoid.getRun()){
           //move object randomly (each object has different pattern)
           if(generator.nextInt(2)==1)
           x3 = x3+generator.nextInt(7);
           else
           x3 = x3-generator.nextInt(7);
           y3 = y3-generator.nextInt(12);
           if(y3 < -30){
                x3=generator.nextInt(470);
                y3=500;}
           x1 = avoid.getx1();
           y1 = avoid.gety1();
        if ((x1+ 30>x3 && x1-30<x3)&&(y1+ 30>y3 && y1-30<y3))
              {
                GameOver();
               }
           avoid.set3(x3,y3);
           avoid.drawSurface.repaint();}
           try{
        //wait 10 milliseconds
           Thread.sleep(10);}
           catch(InterruptedException e) {
               System.out.println("Interrupt Caught");
      }}}}