Question

IN JAVA USING ECLIPSE The objective of this assignment is to create your own hash table class to hold employees and their ID numbers. You'll create an employee class to hold each person's key (id number) and value (name). Flow of the main program: Create an instance of your hash table class in your main method. Read in the Employees.txt file and store the names and ID numbers into Employee objects and store those in your hash table using the SIMPLE modulo operator (%) hash function that we covered in class: "key%N" where N is the size of your array. After you stored all the data in the table, print out all the employee names and their corresponding id numbers. Pick a random employee's ID number and then search for them in the hash table and retrieve their name, print it to the screen. Requirements: 1) Your hash table class must have an array of Employee objects 2) Use the Linear probing technique to handle collisions when you add or search the table 3) You hash function code should be in its own method in the hash table class, NOT in your main method. 4) Your Employee class must contain the ID number and the name You don't have to worry about removing data from the table or keeping track of “Empty Since Start” or “Empty After Removal” buckets. Treat all empty buckets as "Empty since start". You must have these 3 classes: Main.java, HashTable.java, Employee.java

Answer 1

/*Test Main java program for Employee.java and HashTable.java classes*/
//Main.java
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class Main
{
   //Create a HashTable class object of size,53 (Random prime number )
   //53 is taken for best results ,larger the size best results
   private static HashTable hashtable=new HashTable(53);
   public static void main(String[] args)
   {
      
       String fileName="empdata.txt";
       Scanner filereader=null;
       try
       {
           filereader=new Scanner(new File(fileName));
           //read data from file
           while(filereader.hasNextLine())
           {
               String data[]=filereader.nextLine().trim().split(",");
               int id=Integer.parseInt(data[0]);
               String name=data[1];
               //Add to the hash table
               hashtable.addEmployee(new Employee(id, name));
           }
          
           filereader.close();
           System.out.println("HASH TABLE ");

           //print to console hash table
           System.out.println(hashtable.toString());  
           Scanner console=new Scanner(System.in);
          
           System.out.println("Enter a employee id #:");
           //read emp id
           int idNumber=Integer.parseInt(console.nextLine());
          
           //Call method to get the emp by id number
           Employee emp=hashtable.getByID(idNumber);
           //check if emp is not null
           if(emp!=null)
           {
               //print emp object
               System.out.println("Employee found!");
               System.out.println(emp.toString());
           }
           else
           {
               System.out.println("Employee "+idNumber+" is not found in hash table.");
           }      
       }
       catch (FileNotFoundException e)
       {
           System.out.println(e.getMessage());
       }
   }  
}

---------------------------------------------------------------------------------------------------------------------------------------

//HashTable.java
public class HashTable
{
   private int N;
   private Employee emps[];
   public HashTable(int size)
   {
       N=size;
       //create an array of size,N
       emps=new Employee[N];
   }
   /*Method to add Employee object to hash table */
   public void addEmployee(Employee emp)
   {
       int k=emp.hashCode();      
       int index=Math.abs(k%N);
       emps[index]=emp;

   }

   /*Returns the object with id number*/
   public Employee getByID(int id)
   {
       Employee emp=null;
       for(Employee temp: emps)
           if(temp!=null)
               if(temp.getId()==id)
                   return temp;
       return emp;
   }
   /*Returns the string represenation of hash table*/
   public String toString() {
       String data=String.format("%-10s\t%-20s\n", "ID","Name");
       for(Employee emp: emps)
       {
           if(emp ==null)
               data+="NULL"+"\n";
           else
               data+=emp.toString();
       }
       return data;
   }
}

---------------------------------------------------------------------------------------------------------------------------------------
//Employee.java
public class Employee
{
   //private data variables
   private int id;
   private String name;
   /*default constructor*/
   public Employee()
   {
       id=0;
       name="N/A";
   }
   /*Parameterized constructor*/
   public Employee(int id, String name)
   {
       this.id=id;
       this.name=name;
   }
   /**
   * return the id
   */
   public int getId() {
       return id;
   }
   /**
   * id the id to set
   */
   public void setId(int id) {
       this.id = id;
   }
   /**
   * return the name
   */
   public String getName() {
       return name;
   }
   /**
   * name the name to set
   */
   public void setName(String name)
   {
       this.name = name;
   }
   /*Returns the hash code*/
   public int hashCode()
   {
       final int prime = 31;
       int result = 1;
       result = prime * result + id;
       result = prime * result + ((name == null) ? 0 : name.hashCode());
       return result;
   }
   public String toString()
   {
       return String.format("%-10d\t%-20s\n", getId(),getName());
   }
} //end of class

---------------------------------------------------------------------------------------------------------------------------------------

Input file:

empdata.txt

135,John Peterman
160,Joe Divola
101,David Putty
68,Jerry Seinfeld
225,George Costanza
100,Elaine Benes
200,Cosmo Kramer

Sample Output:

HASH TABLE
ID     Name
NULL
NULL
135    John Peterman   
NULL
NULL
NULL
101    David Putty   
NULL
NULL
NULL
NULL
NULL
100    Elaine Benes
NULL
NULL
225    George Costanza   
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
68     Jerry Seinfeld
NULL
NULL
NULL
NULL
NULL
160    Joe Divola
NULL
NULL
200    Cosmo Kramer
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL
NULL

Enter a employee id #:
200
Employee found!
200    Cosmo Kramer