Question

In JAVA :

There are two text files with the following information stored in them:

The instructor.txt file where each line stores the id, name and affiliated department of an instructor separated by a comma The department.txt file where each line stores the name, location and budget of the department separated by a comma

You need to write a Java program that reads these text files and provides user with the following menu:

1. Enter the instructor ID and I will provide you with the name of the instructor, affiliated department and the location of that department.

2. Enter the department name and I will provide you with the location, budget and names of all instructors that work for the department.

3. Insert a record about a new instructor.

4. Exit

The above menu should continue to be displayed in a loop until the user selects option 4.

When the user selects option 1 above, the following should be displayed:

Enter the instructor ID:

If the user enters an instructor id that is not present in the text file, display "The ID doesnot appear in the database.", otherwise, display the name of the instructor, affiliated department and the location of that department.

When the user selects option 2 above, the following should be displayed:

Enter the department name:

If the user enters a name that is not present in the text file, display "The department name doesnot appear in the database.", otherwise, display the location, budget and names of all instructors that work for the department.

If the user selects option 3 above, display the following:

Enter the instructor id:

Enter the instructor name:

Enter the affiliated department name:

Once the user enters the above information, store the information in the instructor file only if the following two conditions are met: 1. The department already exists in the department file. If not, display "The department doesnot exist and hence the instructor record cannot be added to the database". 2. The instructor id should not already be present in the file. If so, display "Instructor id already exists in the file"

The program should work for any number of rows in the two text files.

The code should use good programming practices with sensible variable names, proper indentation and comments where needed.

Answer 1

Here is your program: 3 classes, one driver, one is department and one is instructor class. (screenshot and text code included)

Code Screenshot

Code ((Text))

import java.io.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class DatabaseManager {

    public static void main(String[] args) throws Exception {
        //Store instructor from file.
        List<Instructor> instructorList = new ArrayList<>();
        //Store departments from file.
        List<Department> departmentList = new ArrayList<>();

        /* Read and store department from department.txt */
        try {
            //file input stream object to get stream of file.
            FileInputStream stream = new FileInputStream("department.txt");
            //scanner to read line by line.
            Scanner scanner = new Scanner(stream);
            //read line by line until there is line.
            while (scanner.hasNextLine()) {
                String line = scanner.nextLine();
                //If line is empty, read next line.
                if (line.trim().isEmpty())
                    continue;
                //Split all the data with comma.
                String[] data = line.split(",");
                //Create new department and put it into list.
                Department department = new Department(
                        data[0], data[1], Double.valueOf(data[2]));
                departmentList.add(department);
            }
            stream.close();
        } catch (FileNotFoundException fe) {
            System.out.println("Unable to read department.txt");
        } catch (IOException e) {
            e.printStackTrace();
        }

        /* Start reading instructors from file and insert in list */
        try {
            FileInputStream stream = new FileInputStream("instructor.txt");
            Scanner scanner = new Scanner(stream);
            while (scanner.hasNextLine()) {
                String[] data = scanner.nextLine().split(",");
                Instructor instructor = new Instructor(
                        Integer.parseInt(data[0]), data[1], data[2]);
                instructorList.add(instructor);
            }
            stream.close();
        } catch (FileNotFoundException fe) {
            System.out.println("Unable to read instructor.txt");
        } catch (IOException e) {
            e.printStackTrace();
        }
        /* buffered writer use to write new instructor to the instructor list. */
        BufferedWriter writer;

        /* Create output stream for instructor file. */
        try {
            FileOutputStream stream = new FileOutputStream("instructor.txt", true);
            writer = new BufferedWriter(new OutputStreamWriter(stream));
        } catch (FileNotFoundException fe) {
            System.out.println("Unable to open instructor.txt for writing.");
            writer = null;
            System.exit(0);
        }
        //Scanner object to read user input.
        Scanner input = new Scanner(System.in);

        //Flag for exiting loop if user select to exit.
        boolean exitProgram = false;
        //Loop until user choice to exit. or something happens wrong.
        while (!exitProgram) {
            //Print the menu
            System.out.println("1. Enter the instructor ID and I will provide " +
                    "you with the name of the instructor, " +
                    "affiliated department and the location of that department.");

            System.out.println("2. Enter the department name and I will provide you " +
                    "with the location, budget and names of all instructors " +
                    "that work for the department.");

            System.out.println("3. Insert a record about a new instructor.");

            System.out.println("4. Exit");

            System.out.println("Enter choice[1-4]: ");

            //Read the user choice.
            String choice = input.nextLine();

            switch (choice) {
                //User choose to display instructor.
                case "1":
                    System.out.print("Enter instructor ID: ");
                    //Read instructor id
                    int id = input.nextInt();
                    //Skip the new line (it will come with integer input)
                    input.nextLine();
                    //Loop through instructor list and find.
                    Instructor instructor = null;
                    for (Instructor ins : instructorList) {
                        if (ins.id == id) {
                            //If instructor found, get it reference and break the loop.
                            instructor = ins;
                            break;
                        }
                    }

                    //If instructor is null, it means instructor not found.
                    if (instructor == null) {
                        System.out.println("The ID doesnot appear in the database.");
                    } else {
                        //Now find the instructor department.
                        for (Department department : departmentList) {
                            //If found, display the information and break the loop.
                            if (instructor.department.equals(department.name)) {
                                System.out.println("Instructor Name: " + instructor.name);
                                System.out.println("Department Name: " + instructor.department);
                                System.out.println("Department Location: " + department.location);
                                break;
                            }
                        }
                    }
                    break;

                case "2":
                    //User choose to display department.
                    System.out.print("Enter the department name:");
                    //Read the department name.
                    String dept = input.nextLine();
                    Department department = null;
                    //Search for department.
                    for (Department d : departmentList) {
                        if (d.name.equals(dept)) {
                            department = d;
                            break;
                        }
                    }
                    //if found display the information else display error.
                    if (department == null) {
                        System.out.println("The department name doesnot appear in the database.");
                    } else {
                        System.out.println("Department Location: " + department.location);
                        System.out.println("Department Budget: " + department.budget);
                        System.out.println("Instructor List: ");

                        for (Instructor i : instructorList) {
                            if (i.department.equals(department.name)) {
                                System.out.println(i.name);
                            }
                        }
                    }
                    break;

                case "3":
                    //User choose to enter new instructor.
                    //Read the detail of instructor.
                    System.out.print("Enter the instructor id:");
                    int insId = input.nextInt();
                    input.nextLine();
                    System.out.print("Enter the instructor name:");
                    String insName = input.nextLine();
                    System.out.print("Enter the affiliated department name:");
                    String insDept = input.nextLine();

                    //Flag for dept, and id
                    boolean isDeptExist = false;
                    boolean isInsIdExist = false;
                    //Check for department existence.
                    for (Department d : departmentList) {
                        if (d.name.equals(insDept)) {
                            isDeptExist = true;
                            break;
                        }
                    }

                    //Check for instructor id existence.
                    for (Instructor i : instructorList) {
                        if (i.id == insId) {
                            isInsIdExist = true;
                            break;
                        }
                    }
                    //If id found in list, display error.
                    if (isInsIdExist) {
                        System.out.println("Instructor id already exists in the file");

                    }
                    //else if department not found, display error.
                    else if (!isDeptExist) {

                        System.out.println("The department doesnot exist and hence the " +
                                "instructor record cannot be added to the database");
                    }
                    //Else enter the instructor, and append in the file too.
                    else {
                        Instructor instructor1 = new Instructor(insId, insName, insDept);
                        instructorList.add(instructor1);
                        writer.write(String.format("%d,%s,%s\n", insId, insName, insDept));
                    }
                    break;

                case "4":
                    //Exit the program.
                    exitProgram = true;
                    break;
            }

        }
    }
}

//Instructor class
class Instructor {
    int id;
    String name;
    String department;

    public Instructor(int id, String name, String department) {
        this.id = id;
        this.name = name;
        this.department = department;
    }


}

//Department class
class Department {
    String name;
    String location;
    double budget;

    public Department(String name, String location, double budget) {
        this.name = name;
        this.location = location;
        this.budget = budget;
    }
}

Output