CodingForums.com - "Student Not Found" Problem

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"Student Not Found" Problem

I'm trying to display a message that informs the user that the name he entered was not found in the list of students. I wrote a binary search to go through the list of names to compare to the search key.

Code:

                while(repeat)

                {

                        searchEntry = JOptionPane.showInputDialog("Enter the last name of the student you wish to see the grade of: ");

                        if(searchEntry.length() == 0)

                        {

                                System.exit(0);

                        }

                        int low = 0;

                        int high = studentArray.length - 1;

                

                        while(high >= low)

                        {

                                int mid = (low+high)/2;

                                if(searchEntry.compareToIgnoreCase(studentArray[mid].getLastName()) < 0)

                                {

                                        high = mid - 1;



                                }

                                else if(searchEntry.compareToIgnoreCase(studentArray[mid].getLastName()) > 0)

                                {

                                        low = mid + 1;

                                }

                                else if(searchEntry.compareToIgnoreCase(studentArray[mid].getLastName()) == 0)

                                {

                                        JOptionPane.showMessageDialog(null, studentArray[mid].firstName + " " + studentArray[mid].getLastName() 

                                                                                                                + " received a grade of " + studentArray[mid].getNumberGrade());

                                        high = -1;

                                }

                                else

                                {

                                        JOptionPane.showMessageDialog(null, "Name not found.");

                                }

                        }

                }

Here, I'm using an if-else-if statement, but it is not working the way I want it to.

The first question to ask - has studentArray been sorted prior to this point?
I'll take a look at this when I get home as well.

Yes, the array of objects called studentArray has already been sorted in alphabetical order according to last name.

Looks alright to me; you'll never get to the else condition though. The search entry will always be <, = or > the current iteration, regardless of if it exists in the list.
If you make it through the list without a result, then you have no entry found.

Code:

                        int low = 0;

                        int high = studentArray.length - 1;

                

                        Student result = null;

                        while(high >= low)

                        {

                                int mid = (low+high)/2;

                                if(searchEntry.compareToIgnoreCase(studentArray[mid].getLastName()) < 0)

                                {

                                        high = mid - 1;



                                }

                                else if(searchEntry.compareToIgnoreCase(studentArray[mid].getLastName()) > 0)

                                {

                                        low = mid + 1;

                                }

                                else if(searchEntry.compareToIgnoreCase(studentArray[mid].getLastName()) == 0)

                                {

                                        result = studentArray[mid];

                                        high = -1;

                                }

                        }

                        if (result != null)

                        {

                                System.out.println("Student found: " + result);

                        }

                        else

                        {

                                System.out.println("No student with last name: " + searchEntry);

                        }

The algorithm is otherwise correct.

So how exactly would I make a message display only if no match is found? Delete the else statement, and then make an if outside of the while loop? But what could I make as the condition of this if statement?

The if would just become if (result == null) to indicate that no match is found.

you sir, are awesome. Thank you very much.