Drawing in a Window - Beginning Java - page 1014

package name to distinguish it from the inner class type Rectangle . The constructor is protected because
it is only called by inner class constructors.
The return type for the getBounds() method that makes the bounding rectangle for an element available
is fully qualified by the package name. This is to avoid confusion with your own Rectangle class that you
add as an inner class later in this chapter.
There are two abstract methods that must be implemented by the subclasses. This means that the Ele-
ment class must be declared as abstract . An implementation of the draw() method draws an element using
the Graphics2D object that is passed to it. The modify() method alters the definition of an element using
the Point objects that are passed to it as defining points.
Storing Shapes in the Model
Even though you haven't defined the classes for the shapes that Sketcher creates, you can implement the
mechanism for storing them in the SketcherModel class. You'll store all of them as objects of type Ele-
ment , so you can use a LinkedList<Element> collection class object to hold an arbitrary number of Ele-
ment objects. The container for Element references needs to allow deletion as well as additions to the con-
tents, and you will want to remove items and rearrange the order of items, too. This makes a linked list the
best choice. A map container just doesn't apply to Sketcher data. An ArrayList<> or a Vector<> contain-
er doesn't really fit the bill. Neither is it very efficient when you want to remove items on a regular basis
whereas deleting a shape from a linked list is fast.
You can add a member to the SketcherModel class that you defined earlier in the Sketcher program to
store elements:
import java.io.Serializable;
import java.util.*;
public class SketcherModel extends Observable implements Serializable {
// Detail of the rest of class to be filled in later...
protected LinkedList<Element> elements = new LinkedList<>();
private final static long serialVersionUID = 1001L;
}
You definitely want methods to add and delete Element objects. It is also very useful if the Sketcher-
Model class implements the Iterable<Element> interface because that allows a collection-based for loop
to be used to iterate over the Element objects stored in the model. Here's how the class looks to accommod-
ate that:
import java.io.Serializable;
import java.util.*;
public class SketcherModel extends Observable
implements Serializable, Iterable<Element> {
//Remove an element from the sketch
public boolean remove(Element element) {
boolean removed = elements.remove(element);