jumping help pls

import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)

/**
 * Write a description of class CopyOfsmaller here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class CopyOfsmaller extends Actor
{ 
    GifImage myGif = new GifImage("ezgif.com-resize.gif");
    private int ySpeed;
    private int apexTimer;
    public Jumper()
    {
    }
    /**
     * Act - do whatever the CopyOfsmaller wants to do. This method is called whenever
     * the 'Act' or 'Run' button gets pressed in the environment.
     */
    public void act() 
    {
      setImage( myGif.getCurrentImage() );
       int speed = 3;
      
      if(Greenfoot.isKeyDown("left"))
      setLocation(getX() - speed, getY());
      if(Greenfoot.isKeyDown("right"))
      setLocation(getX() + speed, getY());
      
      
      int groundLevel = getWorld().getHeight() - getImage().getHeight()/2;
        boolean onGround = (getY() == groundLevel);
        if (!onGround) // in middle of jump
        {
            if (ySpeed == 0 && apexTimer > 0) apexTimer--; // run apex timer
            if (ySpeed == 0 && apexTimer > 0) return; // apex timer still running
            ySpeed++; // adds gravity effect
            setLocation(getX(), getY()+ySpeed); // fall (rising slower or falling faster)
            if (getY()>=groundLevel) // has landed (reached ground level)
            {
                setLocation(getX(), groundLevel); // set on ground
                Greenfoot.getKey(); // clears any key pressed during jump
           }
        }
        else // on ground
        {
            if ("space".equals(Greenfoot.getKey())) // jump key detected
            {
                ySpeed = -15; // add jump speed
                setLocation(getX(), getY()+ySpeed); // leave ground
                apexTimer = 100;  // set apex timer (adjust value to suit)
            }
    }
 }
}