Filing and Printing Documents - Beginning Java 2 SDK - page 936

We first check the sketchChanged flag. If the flag is false , either the sketch is empty, or it hasn't
been changed since the last save. Either way there's no point in writing it to disk, so we return
immediately. We then initialize the local variable, file , with the reference stored in modelFile . If
modelFile was not null , then we skip the entire if and just call the saveSketch() method to
write the file to modelFile - we will get to the detail of the saveSketch() method in a moment.
The condition tested in the next if looks rather complicated but this is primarily due to the plethora of
arguments in the showConfirmDialog() call and we can break the condition down into its
component parts quite easily. There are two logical expressions separated by || so if either is true
then we execute a return . The first expression just checks for file being null so if this is the case
we return immediately. If the first expression is false , file is not null and the second expression
will be evaluated.
This will be true if file references a file that does exist AND the value returned from the
showConfirmDialog() method is JOptionPane.NO _ OPTION . The dialog just warns of the
overwrite potential so if JOptionPane.NO _ OPTION is returned then the user has elected not to
overwrite the file. Remember that with the || operator, if the left operand is true then the right
operand will not be evaluated. Similarly, with the && operator, if the left operand is false then the
right operand will not be evaluated. This means that the showConfirmDialog() method will only be
executed if file is not null - so the left expression for the || is false - and file references a file
that does exist - so the left operand for the && is true . If we don't execute the return, then we fall
through the if to call our helper method saveSketch() with file as the argument.
Writing a Sketch to a File
Writing a sketch to a file just means making use of what we learned about writing objects to a file. We
have already ensured that a SketchModel object is serializable, so we can write the sketch to an
ObjectOutputStream with the following method in SketchFrame :
// Write a sketch to outFile
private void saveSketch(File outFile) {
try {
ObjectOutputStream out = new ObjectOutputStream(
new BufferedOutputStream(
new FileOutputStream(outFile)));
out.writeObject(theApp.getModel()); // Write the sketch to the
// stream
out.close(); // Flush & close it
} catch(IOException e) {
System.err.println(e);
JOptionPane.showMessageDialog(SketchFrame.this,
"Error writing a sketch file.",
"File Output Error",
JOptionPane.ERROR _ MESSAGE);
return; // Serious error - return
}
if(outFile != modelFile) { // If we are saving to a new file
// we must update the window
modelFile = outFile; // Save file reference
filename = modelFile.getName(); // Update the file name
setTitle(frameTitle + modelFile.getPath()); // Change the window title