How can I design Flyweight pattern?

Now I'm studying about Flyweight design pattern. I tried to find some examples through google, and this is what I found.

import java.awt.Color;
import java.awt.Graphics;

public interface Shape {

    public void draw(Graphics g, int x, int y, int width, int height, Color color);
}

This is interface Shape.

import java.awt.Color;
import java.awt.Graphics;

public class Line implements Shape {...}
public class Oval implements Shape {...}

These two class implements Shape interface.

import java.util.HashMap;

public class ShapeFactory {

    private static final HashMap<ShapeType, Shape> shapes = new HashMap<ShapeType, Shape>();

    public static Shape getShape(ShapeType type) {
        Shape shapeImpl = shapes.get(type);

        if (shapeImpl == null) {
            if (type.equals(ShapeType.OVAL_FILL)) {
                shapeImpl = new Oval(true);
            } else if (type.equals(ShapeType.OVAL_NOFILL)) {
                shapeImpl = new Oval(false);
            } else if (type.equals(ShapeType.LINE)) {
                shapeImpl = new Line();
            }
            shapes.put(type, shapeImpl);
        }
        return shapeImpl;
    }
    
    public static enum ShapeType {
        OVAL_FILL, OVAL_NOFILL, LINE;
    }
}

Through this Factory class, Oval or Line class is made by the type. I understand it but I have one question about it. I learn that Static field or function can only use in Static class. However, in this example, static Hashmap and function is declared in non-static class ShapeFactory. I found other examples in google, but every examples are similar to this. I tried to do my own Flyweight model, but it does not work. Can anyone explain about this?