Code doesnt work?

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

/**
 * Write a description of class Player here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class Player extends Actor
{
    /**
     * Act - do whatever the Player wants to do. This method is called whenever
     * the 'Act' or 'Run' button gets pressed in the environment.
     */
    
    private GreenfootImage left = new GreenfootImage("left.jpg");  
private GreenfootImage right= new GreenfootImage("right.jpg"); 
    
    public void act() 
{
if (Greenfoot.isKeyDown("right"))
move (4);
if (Greenfoot.isKeyDown ("left"))
move (-4);
}
}