mainframe.java~1~

用JAVA实现的小的学生管理系统.JAVA与数据库的结合使用.

				      // call.
				      JOptionPane.showMessageDialog(null, 
					message,
					"Request Denied",
					JOptionPane.WARNING_MESSAGE);
				}
				else {
					// Attempt to enroll the student, noting
					// the status code that is returned.
					int success =
						selected.enroll(currentUser);

					// Report the status to the user.
					if (success == Section.SECTION_FULL) {
					    JOptionPane.showMessageDialog(
						null, 
						"Sorry - that section is full.",
						"Request Denied",
						JOptionPane.WARNING_MESSAGE);
					}
					else if (success == 
						 Section.PREREQ_NOT_SATISFIED) {
					    JOptionPane.showMessageDialog(
						null, 
						"You haven't satisfied all " +
						"of the prerequisites for " +
						"this course.",
						"Request Denied",
						JOptionPane.WARNING_MESSAGE);
					}
					else if (success == 
						 Section.PREVIOUSLY_ENROLLED) {
				            String[] message = 
					      { "You are already enrolled in " +
					            "(or have already",
					        "successfully completed) a " +
						    "section of this course.",
						" " };

					    JOptionPane.showMessageDialog(
						null, 
						message,
						"Request Denied",
						JOptionPane.WARNING_MESSAGE);
					}
					else { // success!
					    // Display a confirmation message.
					    JOptionPane.showMessageDialog(
						null, 
						"Seat confirmed in " +
						    selected.
						        getRepresentedCourse().
						        getCourseNo() + ".",
						"Request Successful",
						JOptionPane.INFORMATION_MESSAGE);

					    // Update the list of sections 
					    // that this student is 
					    // registered for.
					    studentCourseList.setListData(
						currentUser.
						getSectionsEnrolled());

					    // Update the field representing
					    // student's course total.
					    int total = 
						currentUser.getCourseTotal();
					    totalCoursesLabel.setText("" + 
								      total);

					    // Clear the selection in the
					    // schedule of classes list.
					    scheduleOfClassesList.
						clearSelection();
					}
				}

				// Check states of the various buttons.
				resetButtons();
			}
		};
		addButton.addActionListener(aListener);

		// dropButton

		aListener = new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				// Determine which section is selected
				// (note that we must cast it, as it
				// is returned as an Object reference).
				Section selected = (Section)
					studentCourseList.getSelectedValue();

				// Drop the course.
				selected.drop(currentUser);

				// Display a confirmation message.
				JOptionPane.showMessageDialog(null, 
					"Course " + selected.
					    getRepresentedCourse().
					    getCourseNo() + " dropped.",
					"Request Successful",
					JOptionPane.INFORMATION_MESSAGE);

				// Update the list of sections that 
				// this student is registered for.
				studentCourseList.setListData(
					currentUser.
					getSectionsEnrolled());

				// Update the field representing
				// student's course total.
				int total = currentUser.getCourseTotal();
				totalCoursesLabel.setText("" + total);

				// Check states of the various buttons.
				resetButtons();
			}
		};
		dropButton.addActionListener(aListener);

		// saveScheduleButton

		aListener = new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				boolean success = currentUser.persist();
				if (success) {
				        // Let the user know that his/her
					// schedule was successfully saved.
				        JOptionPane.showMessageDialog(null, 
						"Schedule saved.", 
						"Schedule Saved",
						JOptionPane.INFORMATION_MESSAGE);
				}
				else {
				        // Let the user know that there
					// was a problem.
				        JOptionPane.showMessageDialog(null, 
						"Problem saving your " +
						"schedule; please contact " +
						"the SRS Support Staff for " +
						"assistance.",
						"Problem Saving Schedule",
						JOptionPane.WARNING_MESSAGE);
				}
			}
		};
		saveScheduleButton.addActionListener(aListener);

		// logoffButton

		aListener = new ActionListener() {
			public void actionPerformed(ActionEvent e) {
				clearFields();
				ssnField.setText("");
				currentUser = null;

				// Clear the selection in the
				// schedule of classes list.
				scheduleOfClassesList.clearSelection();

				// Check states of the various buttons.
				resetButtons();
			}
		};
		logoffButton.addActionListener(aListener);

		// studentCourseList

		lListener = new ListSelectionListener() {
			public void valueChanged(ListSelectionEvent e) {
				// When an item is selected in this list,
				// we clear the selection in the other list.
				if (!(studentCourseList.isSelectionEmpty())) 
					scheduleOfClassesList.clearSelection();

				// Check states of the various buttons.
				resetButtons();
			}
		};
		studentCourseList.addListSelectionListener(lListener);

		// scheduleOfClassesList

		lListener = new ListSelectionListener() {
			public void valueChanged(ListSelectionEvent e) {
				// When an item is selected in this list,
				// we clear the selection in the other list.
				if (!(scheduleOfClassesList.isSelectionEmpty())) 
					studentCourseList.clearSelection();

				// Check states of the various buttons.
				resetButtons();
			}
		};
		scheduleOfClassesList.addListSelectionListener(lListener);

		wListener = new WindowAdapter() {
			public void windowClosing(WindowEvent e) {
				System.exit(0);
			}
		};
		this.addWindowListener(wListener);

              	this.setVisible(true);
         }

	// Because there are so many different situations in which one or
	// more buttons need to be (de)activated, and because the logic is
	// so complex, we centralize it here and then just call this method
	// whenever we need to check the state of one or more of the buttons.  
	// It is a tradeoff of code elegance for execution efficiency:  
	// we are doing a bit more work each time (because we don't need to 
	// reset all four buttons every time), but since the execution time
	// is minimal, this seems like a reasonable tradeoff.
	private void resetButtons() {
		// There are four conditions which collectively govern the
		// state of each button:
		//	
		// o	Whether a user is logged on or not.
		boolean isLoggedOn;
		if (currentUser != null) isLoggedOn = true;
		else isLoggedOn = false;
		
		// o	Whether the user is registered for at least one course.
		boolean atLeastOne;
		if (currentUser != null && currentUser.getCourseTotal() > 0)
			atLeastOne = true;
		else atLeastOne = false;

		// o	Whether a registered course has been selected.
		boolean courseSelected;
		if (studentCourseList.isSelectionEmpty()) 
			courseSelected = false;
		else courseSelected = true;
		
		// o    Whether an item is selected in the Schedule of Classes.
		boolean catalogSelected;
		if (scheduleOfClassesList.isSelectionEmpty()) 
			catalogSelected = false;
		else catalogSelected = true;

		// Now, verify the conditions on a button-by-button basis.

		// Drop button:
		if (isLoggedOn && atLeastOne && courseSelected)
			dropButton.setEnabled(true);
		else dropButton.setEnabled(false);

		// Add button:
		if (isLoggedOn && catalogSelected)
			addButton.setEnabled(true);
		else addButton.setEnabled(false);

		// Save My Schedule button:
		if (isLoggedOn) {
			saveScheduleButton.setEnabled(true);

			// Because of the way that we created the latter two 
			// buttons, we have do a bit of extra work to make them
			// APPEAR to be turned on or off.
			l1.setEnabled(true); 
			l2.setEnabled(true); 
		}
		else {
			saveScheduleButton.setEnabled(false);
			l1.setEnabled(false); 
			l2.setEnabled(false); 
		}

		// Log Off button:
		if (isLoggedOn) logoffButton.setEnabled(true);  
		else logoffButton.setEnabled(false);  
	}

	// Called whenever a user is logged off.
	private void clearFields() {
		nameField.setText("");
		totalCoursesLabel.setText("");
		studentCourseList.setListData(new Vector());
	}

	// Set the various fields, lists, etc. to reflect the information
	// associated with a particular student.  (Used when logging in.)
	private void setFields(Student theStudent) {
		nameField.setText(theStudent.getName());
		int total = theStudent.getCourseTotal();
		totalCoursesLabel.setText("" + total);
	
		// If the student is registered for any courses, list these, too.
		if (total > 0) {
			// Because we already have a vector containing the
			// sections that the student is registered for, 
			// and because these objects have defined a toString()
			// method, we can merely hand the vector to the JList.
			studentCourseList.setListData(theStudent.
				getSectionsEnrolled());
		}
	}
 }