Circular Doubly Linked List Program in Java (Homework Help)

Question

Basically the program is supposed to create a "round table" of executives, with a chairman who cannot be changed. I kinda sorta almost know what I'm doing and I'm about halfway through my methods for inserting and removing executives, but I just tried to test my code to see how it was going and it gets errors as soon as I input the chairpersons information. Also, I'm not really sure at all how I would go about the removeByCorporation method in the ExecutiveList. I'm almost positive that method is nearly all incorrect and I'm just not how to remove a node in a circular doubly linked list like this.

*No need to help me with the printing methods, I simply haven't gotten to them yet.

tl;dr: 1) Why is it crashing right away? 2) I'm pretty sure my removeByCorporation method is totally wrong. If it is, any suggestions or help on how to fix it?

Here are the two classes I'm having trouble with, if you'd like to see the other ones let me know and I'll post them, but they're 99% getters and setters.

FIRST CLASS

public class ExecutiveList {

private ExecutiveNode chair;
ExecutiveNode cursor;

public ExecutiveList() {

}

public ExecutiveList (Executive chairperson) {

    chair.setExecutive(chairperson);
    chair.left = chair;
    chair.right = chair;
}

public void insertLeftOfChair(Executive exec) {

    ExecutiveNode newExec = new ExecutiveNode();
    newExec.setExecutive(exec);
    chair.setLeft(newExec);

}

public boolean insertRightOfExec (Executive exec, String target) {
    cursor = chair;
    ExecutiveNode newExec = new ExecutiveNode();

    do { cursor = cursor.getLeft();
    if (cursor.getExecutive().equals(exec)) {
        newExec.setExecutive(exec);
        cursor.getRight().setLeft(newExec);
        newExec.setLeft(cursor);
        newExec.setRight(cursor.getRight());
        cursor.setRight(newExec);
        return true;
    }
    else {
        return false;
    }
    }       while (cursor.getExecutive().getExecutiveName() != target);


}

public boolean insertLeftOfExec (Executive exec, String target) {
    cursor = chair;
    ExecutiveNode newExec = new ExecutiveNode();
    do { cursor = cursor.getLeft();
        if (cursor.getExecutive().equals(exec)) {
            newExec.setExecutive(exec);
            cursor.getLeft().setRight(newExec);
            newExec.setRight(cursor);
            newExec.setLeft(cursor.getRight());
            cursor.setLeft(newExec);

            return true;
        }
        else {
            return false;
        }
    }       while (cursor.getExecutive().getExecutiveName() != target);
}

public boolean removeTargetExec(String name) {
    if (chair.equals(name)) {
        return false;
    }
    else {
        return false;
    }
}

public int removeByCorporation(String corporation) {
    int removed = 0;
    cursor = chair;
    do {
        if (cursor.getExecutive().getCompanyName().equals(corporation)) {
            cursor.setExecutive(null);
            cursor.getLeft();
            removed = removed + 1;
        }
    } while (removed > 0);

    return removed;
}

public void printByCorporation(String corporation) {

}

public void printAllClockwise() {

}

public void printAllCounterClockwise() {

}
    }

SECOND CLASS

import java.util.Scanner;

    public class MeetingManager {
public static void main(String[] args) {

    // scanner to read the users input
    Scanner input = new Scanner(System.in);

    // strings to pass information about the chairperson
    String chairpersonName;
    String chairpersonCompany;

    // strings to pass information about executives other
    // than the chairperson
    String execName;
    String execCompany;
    String target;

    // holds information on whether on not an operation
    // was successful and how many executives were removed
    // for the remove by corporation command.
    boolean success;
    int numRemoved = 0;

    // prompts the user for information about the chairperson
    // and sets it to an executive object name chairperson
    System.out.println("Enter the name of the chairperson: ");
    chairpersonName = input.next();
    if (chairpersonName.length() < 1) {
        System.out.println("Please enter a full name");
    }
    System.out.println("Enter the company of the chairperson: ");
    chairpersonCompany = input.next();
    if (chairpersonCompany.length() < 1) {
        System.out.println("Please enter a full name");
    }
    Executive chairperson = new Executive(chairpersonName, chairpersonCompany);

    // creates a new ExecutiveList object and passes information
    // about the chairperson
    ExecutiveList list = new ExecutiveList(chairperson);

    // for loop to repeatedly print the menu and take instructions
    // from the user until they choose to exit.
    for (int i = 1; i > 0; i++) {
        ShowMenu();
        String option = input.next();

        // error message for improper input
        if (option.length() > 3) {
            System.out.println("You can only enter one option");
        }

        // insert left of chairperson
        else if (option.toUpperCase().equals("ILC")) {
            System.out.println("Enter the executives name: ");
            execName = input.next();
            System.out.println("Enter the executives company: ");
            execCompany = input.next();
            Executive newGuy = new Executive(execName, execCompany);
            list.insertLeftOfChair(newGuy);
            System.out.println("Insertion successful.");
        }

        // insert left of executive
        else if (option.toUpperCase().equals("ILE")) {
            System.out.println("Enter the executives name: ");
            execName = input.next();
            System.out.println("Enter the executives company: ");
            execCompany = input.next();
            Executive newGuy = new Executive(execName, execCompany);
            System.out.println("Enter the name of the target executive: ");
            target = input.next();

            success = list.insertLeftOfExec(newGuy, target);
            if (success == true) {
                System.out.println("Insertion successful.");
            }
            else {
                System.out.println("The executive could not be inserted.");
            }
        }


        // insert right of executive
        else if (option.toUpperCase().equals("IRE")) {
            System.out.println("Enter the executives name: ");
            execName = input.next();
            System.out.println("Enter the executives company: ");
            execCompany = input.next();
            Executive newGuy = new Executive(execName, execCompany);
            System.out.println("Enter the name of the target executive: ");
            target = input.next();

            success = list.insertRightOfExec(newGuy, target);
            if (success) {
                System.out.println("Insertion successful.");
            }
            else {
                System.out.println("The executive could not be inserted.");
            }
        }

        // remove target executive
        else if (option.toUpperCase().equals("RTE")) {
            System.out.println("Enter the name of the executive to remove: ");
            execName = input.next();
            success = list.removeTargetExec(execName);

            if (execName.equals(chairpersonCompany))
                list.removeTargetExec(execName);
            if (success) {
                System.out.println(execName + " has been removed from the meeting.");
            }
            else {
                System.out.println(execName + " could not be found.");
            }
        }

        // remove by corporation
        else if (option.toUpperCase().equals("RBC")) {
            System.out.println("Enter the name of the corporation to remove: ");
            execCompany = input.next();
            numRemoved = list.removeByCorporation(execCompany);
            if (execCompany.equals(chairperson.getCompanyName())) {
                System.out.println("Invalid command: cannot remove all employees from the chairperson's corporation");
            }
            else if (numRemoved < 1) {
                System.out.println("That corporation could not be found and no executives were removed.");
            }
            else {
                System.out.println(numRemoved + " executive(s) from " + execCompany + " have been removed from the meeting.");
            }
        }

        // prints by corporation
        else if (option.toUpperCase().equals("PBC")) {
            System.out.println("Enter the name of a corporation to display: ");
            execCompany = input.next();
            list.printByCorporation(execCompany);
        }

        // prints all counter-clockwise
        else if (option.toUpperCase().equals("PCC")) {

            list.printAllCounterClockwise();
        }

        // prints all clockwise
        else if (option.toUpperCase().equals("PCL")) {

            list.printAllClockwise();
        }

        else if (option.toUpperCase().equals("EXT")) {
            System.out.println("Terminating program...");
            break;
        }

        // Error message
        else {
            System.out.println("Please select a valid option.");
        }

    }

}



// displays menu and prompts user for input
public static void ShowMenu() {
    System.out.println("\nILC) Insert an executive to the left of the chairperson\nILE) Insert an executive to the left of a given executive\nIRE) Insert an executive to the right of a given executive\nRTE) Remove Target Executive");
    System.out.println("RBC) Remove By Corporation\nPBC) Print By Corporation\nPCC) Print all in counter-clockwise order\nPCL) Print all in clockwise order\nEXT) Exit the program\n\nSelect a menu option: ");
}

}

Finally, thank you to anyone who gives any sort of suggestion or advice or actual help in any way shape or form. I know people get angry when they see homework questions for some reason because they think the student is asking them to "do their homework for me", but that's not what I'm doing. I'd simply like any advice or tips, I'm not asking you to just fill in the blanks for me and fix everything (not that I'd be opposed to it :P). Thanks.

Answer 1

The trick is to make sure that, on EVERY operation, you update the item being changed and the two others which reference it (quite handily in a doubly linked list, the two which reference it are also the two it references).

Check each of your methods, and ensure that in each one you are updating 4 fields per change - two in the subject, and one each in the two that are linked from the subject.

Answer 2

In removeByCorporation method , you are just setting the executive to null , but considering this to be a doubly linked list , dont you think you need to set the references of the previous and next executive , so that the doubly linked list doesn't break .