GifImage gifRight = new GifImage("Shroom-Cropped.gif");

GifImage gifLeft = new GifImage(<< filename of other gif >>);
GifImage gifImage = gifRight;

gifImage = gifRight;

import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)
 
/**
 * Write a description of class Shroom here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class Shroom extends Actor
{
    /**
     * Act - do whatever the Shroom wants to do. This method is called whenever
     * the 'Act' or 'Run' button gets pressed in the environment.
     */
    public void act() 
    {
       setImage(gifImage.getCurrentImage()); 
       int speed = 4;
       
      if(Greenfoot.isKeyDown("left"))
      setLocation(getX() - speed, getY());
      "Play 5 images in a order"
       
      if(Greenfoot.isKeyDown("right"));
      setLocation(getX() + speed, getY());
    }
}

import greenfoot.*;

public class Shroom extends Actor
{
    private static final GifImage gifRight = new GifImage("Shroom-Cropped.gif");
    private static final GifImage gifLeft = new GifImae("Shroom-Cropped-Left.gif");
    private GifImage gifImage;
    private int speed = 4;
    
    public void act()
    {
        if(Greenfoot.isKeyDown("left"))
        {
            setLocation(getX() - speed, getY());
            gifImage = gifLeft;
        }        
        if(Greenfoot.isKeyDown("right"));
        {
            setLocation(getX() + speed, getY());
            gifImage = gifRight;
        }
        setImage(gifImage.getCurrentImage());       
    }
}

public void act()
{
    setImage("Shroom-Still.png"); // image when not moving
    if(Greenfoot.isKeyDown("left"))
    {
        setLocation(getX() - speed, getY());
        gifImage = gifLeft;
        setImage(gifImage.getCurrentImage());
    }
    if(Greenfoot.isKeyDown("right"))
    {
        setLocation(getX() + speed, getY());
        gifImage = gifRight;
        setImage(gifImage.getCurrentImage());
    }
}