First Slick Game

import org.newdawn.slick.AppGameContainer;
import org.newdawn.slick.BasicGame;
import org.newdawn.slick.GameContainer;
import org.newdawn.slick.Graphics;
import org.newdawn.slick.Image;
import org.newdawn.slick.Input;
import org.newdawn.slick.SlickException;

public class SimpleGame extends BasicGame{
    Image land = null;
    Image plane = null;
    float x = 400; //plane pos x
    float y = 300; //plane pos y
    float scale = 1.0f; //plane size

    public SimpleGame(){
        super("CLick2DPath2Glory - Simple Game");
    }

    @Override
    public void init(GameContainer gc)throws SlickException{
        land = new Image("fetch.jpg");
        plane = new Image("fetch2.png");
    }

    @Override
    public void update(GameContainer gc, int delta)throws SlickException{
        Input input = gc.getInput();
        if(input.isKeyDown(Input.KEY_A)){
            plane.rotate(-0.2f * delta);
        }
        if(input.isKeyDown(Input.KEY_D)){
            plane.rotate(0.2f * delta);
        }
        if(input.isKeyDown(Input.KEY_W)){
            float hip = 0.4f * delta;

            float rotation = plane.getRotation();

            x+= hip * Math.sin(Math.toRadians(rotation));
            y-= hip * Math.cos(Math.toRadians(rotation));
        }
        if(input.isKeyDown(Input.KEY_2)){
            scale += (scale >= 5.0f) ? 0 : 0.1f;
            plane.setCenterOfRotation(plane.getWidth()/2.0f*scale, plane.getHeight()/2.0f*scale);
        }
        if(input.isKeyDown(Input.KEY_1)){
            scale -= (scale <= 1.0f) ? 0 : 0.1f;
            plane.setCenterOfRotation(plane.getWidth()/2.0f*scale, plane.getHeight()/2.0f*scale);
        }
    }

    public void render(GameContainer gc, Graphics g)throws SlickException{
        land.draw(0,0);
        plane.draw(x, y, scale);
    }

    public static void main(String[] args)throws SlickException{
        AppGameContainer app = new AppGameContainer(new SimpleGame());

        app.setDisplayMode(800, 600, false);
        app.start();
    }
}