Graphics2D graphics = image.createGraphics();
graphics.drawLine(blah blah);

import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)
import java.awt.Graphics;
import java.awt.Color;

public class NormalShot extends awtBased
{
    GreenfootImage canvas;
    int anchorX, anchorY, topX, topY;
    
    int shotMoveSpeed = 1;
    
    public NormalShot(int anchorXtemp, int anchorYtemp)
    {
        anchorX = anchorXtemp;
        anchorY = anchorYtemp;
        topX = anchorX;
        topY = anchorY;
    }

    public void addedToWorldExtended() //called by superclass from addedToWorld()
    {
        setLocation(getWorld().getWidth() / 2, getWorld().getHeight() / 2);
        canvas = new GreenfootImage(getWorld().getWidth(), getWorld().getHeight());
        canvas.setColor(Color.BLACK);
        setImage(canvas);
    }
    
    public void actExtended()  //called by superclass from act()
    {
        drawShot();
    }
    
    public void drawShot()
    {
        topY = topY - shotMoveSpeed;
        canvas.drawLine(anchorX, anchorY, topX, topY);
    }
}

        topY = topY - 1;
        canvas.drawLine(anchorX, anchorY, topX, topY);