Java Reference
In-Depth Information
How It Works
After dealing with saving the current sketch in the
actionPerformed()
member of the
FileAction
class, we use our
showDialog()
method that we defined in the
SketchFrame
class to display a file
open dialog. Our
showDialog()
method is all-purpose - we can put any kind of label on the button or
title in the title bar so we can use it to display any of the dialogs we need for file operations.
If a
File
object was selected in the dialog, we pass this to the
openSketch()
member of
SketchFrame
to read a new sketch from the file. The
openSketch()
method creates an
ObjectInputStream
object from the
File
object passed as an argument, and reads a
SketchModel
object from the stream by calling the
readObject()
method. The object returned by the
readObject()
method has to be cast to the appropriate type -
SketchModel
in our case. We pass
this
SketchModel
object to the
insertModel()
method for the application object. This replaces the
current sketch reference in the
sketch
member of the application object with a reference to the new
sketch, and then sets the view and the application window as observers. Calling
repaint()
for the
view object displays the new sketch, since the
paint()
method for the view object obtains a reference
to the current model by calling the
getModel()
member of the application object, which will return
the reference to the new model.
Starting a New Sketch
The
Fi
le | New
menu item simply starts a new sketch. This is quite similar to the open operation except
that we must create an empty sketch rather than read a new one from disk. The processes of checking
for the need to save the current sketch and inserting the new
SketchModel
object into the application
will be the same.
Try It Out - Implementing the New Operation
We need to place the code to do this in the
else
-
if
block corresponding to the
newAction
object
event. This is in the code in the
actionPerformed()
method in the
FileAction
class:
else if(name.equals(newAction.getValue(NAME))) {
checkForSave();
theApp.insertModel(new SketchModel()); // Insert new empty sketch
modelFile = null; // No file for it
filename = DEFAULT
_
FILENAME; // Default name
setTitle(frameTitle + files.getCurrentDirectory() +
"\\" + filename);
sketchChanged = false; // Not changed yet
}
Now you can create a new sketch.
How It Works
All the saving of the existing sketch is dealt with by our
checkForSave()
method. The new part is the
last five lines of code. We call the
SketchModel
constructor to create a new empty sketch, and pass it
to the
insertModel()
method for the application object. This will insert the new sketch into the
application and get the view object to display it. We then update the data members of the window that
record information about the file for the current sketch and its status. We also set the
sketchChanged
flag to
false
as it's an empty sketch.
