Question

You will create a class to keep student's information: name, student ID, and grade. The program will have the following functionality:
- The record is persistent, that is, the whole registry should be saved on file upon exiting the program, and after any major change.
- The program should provide the option to create a new entry with a student's name, ID, and grade.
- There should be an option to lookup a student from his student ID (this will be the key in the hash table).
- There should be an option to remove a particular entry by providing the student ID.
- There should be an option to display the whole registry, sorted by student ID.
- Remember that the registry must be persistent, so you will have to save all this information to the file system. You may use any of the versions of hash tables implemented in the previous exercise.

Here is my code for it so far, it might not be correct.

public class Student<String, V> extends HashTable<String, V> {
   private V name;
   private String id;
   private int grade;
  
   public V lookup() {
       HashTable<String, V> registry = new HashTable<String, V>();
       Scanner input = new Scanner(System.in);
       System.out.print("Please Enter the Student ID: ");
       id = (String) input.next();
       registry.lookup(id);
       java.lang.String out = "The Student's Name is " + name;
       return (V) out;
   }
  
   public V remove() {
       HashTable<String, V> registry = new HashTable<String, V>();
       Scanner input = new Scanner(System.in);
       System.out.print("Please Enter the Student ID: ");
       id = (String) input.next();
       super.remove(id);
       java.lang.String out = "The Student That Has Been Removed is " + name;
       return (V) out;
   }
  
   public java.lang.String display() {
       HashTable<String, V> registry = new HashTable<String, V>();
       super.getSortedList(null);
       System.out.println(something);
   }
  
   public static void main(java.lang.String[] args) {
       HashTable<String, V> registry = new HashTable<String, V>();
       Scanner input = new Scanner(System.in);
       java.lang.String choice;
       System.out.print("\nWhat Would You Like to Do? Enter a Number:"
                           + "\n1. Lookup Student by ID"
                           + "\n2. Remove an entry with Student ID"
                           + "\n3. Display Registry\n");
       switch (choice) {
       case "1":
           registry.lookupName();
       case "2":
           registry.removeEntry();
       case "3":
           registry.display();
       }
      
   }
}

The 'key' is the student id, and the 'value' is to call the object Student to get the name and letter grade.

I don't understand how to make the registry "persistent'.

Answer 1

//Student.java import java.util.*; import java.io.*; public class Student {    private String name,grade;    int id;    //constructer    public Student(String name,int id,String grade){        this.name=name;        this.id=id;        this.grade=grade;    }       public int getId(){        return id;    }    //getting student    public String toString()    {        return this.id + " "+ this.name+" "+this.grade;    }    //main method    public static void main(String args[]){        Hashtable<Integer,Student> register=new Hashtable<Integer,Student>(); //hashtable        Scanner input = new Scanner(System.in); //input        int option;        int id;          while(true){            System.out.println();            //menu            System.out.print("\nWhat Would You Like to Do? Enter a Number:"                            +"\n1. Inserting new Student"                               + "\n2. Lookup Student by ID"                             + "\n3. Remove an entry with Student ID"                             + "\n4. Display Registry"                             +"\n5.exit\n");            option=input.nextInt();            if(option==5){                break;            }            switch(option){                case 1:                    Student newStudent=createStudent();                    register.put(newStudent.getId(),newStudent);                    try{                        writeToFIle(register); //writing to file                    }                    catch(Exception e){                    }                    break;                case 2:                    System.out.print("Please Enter the Student ID: ");                    id =input.nextInt();                    //found                    if(register.get(id)!=null){                        System.out.println(register.get(id));                    }                    else{                        System.out.println("Student Not found");                    }                    break;                case 3:                     System.out.print("Please Enter the Student ID: ");                    id = input.nextInt();                    if(register.get(id)!=null){                        register.remove(id);//removing student                        try{                            writeToFIle(register); //writing to file                        }                        catch(Exception e){                        }                    }                    else{                        System.out.println("Student Not found");                    }                    break;                case 4:                //displaying register                     List<Integer> v = new ArrayList<Integer>(register.keySet());                    Collections.sort(v);                    for (Integer str : v) {                       System.out.println(str + " " + register.get(str));                    }                    break;            }        }                          try{                writeToFIle(register);            }            catch(Exception e){            }    }    public static Student createStudent(){        String name,grade;        int id;        Scanner sc=new Scanner(System.in);        System.out.printf("Enter id::");        id=sc.nextInt();        System.out.printf("Enter Name::");        name=sc.next();        System.out.printf("Enter Grade::");        grade=sc.next();               return new Student(name,id,grade);    }    public static void writeToFIle(Hashtable<Integer,Student> h) throws IOException{           List<Integer> v = new ArrayList<Integer>(h.keySet());            Collections.sort(v);           String result="";           for (Integer str : v) {               result+=str + " " + h.get(str)+"\n";            }                     File file = new File("register.txt");                // creates the file           file.createNewFile();                  // creates a FileWriter Object           FileWriter writer = new FileWriter(file);                  // Writes the content to the file           writer.write(result);           writer.flush();           writer.close();           System.out.println("Record written to FIle");    } }