jumping

import greenfoot.*;
  
public class Dolphin extends Actor
{
    private int speed = 7;
    private int vSpeed = 0;
    private int acceleration = 2;
    
    public void act() 
    {
       checkKeys();
       checkFall();
    }
    
    private void checkKeys()  
    {
       if(Greenfoot.isKeyDown("left"))
        {
           moveLeft();
        } 
       if(Greenfoot.isKeyDown("right"))
       {
           moveRight();
       }
    }    
    
    public void checkFall()
    {
        if(onGround())
        {
           vSpeed=0; 
        }
        else
        {
            fall();
        }
    }
    
    public boolean onGround()
    {
        Actor under = getOneObjectAtOffset ( 0, getX() / 2, Ground.class);
        return under != null;
    }
    
    public void fall()
    {
        setLocation ( getX(), getY() + vSpeed);
        vSpeed = vSpeed + acceleration;
    }
    
    public void moveRight()
    {
        setLocation ( getX() + speed, getY());
    }
    
    public void moveLeft()
    {
        setLocation ( getX() - speed, getY());
    }
}