Write a Java program that outputs a list of students from the given data file (h

Question

Write a Java program that outputs a list of students from the given data file (home.txt). You have to input the name of the data file from keyboard. You have to use input.hasNext()with while loop when your program reads tokens from the file. We are assuming that you don’t know how many lines are in the data file. The file contains student name followed by their hometown. Your program should output each hometown, total number of students from each hometown, and each student’s name belonging in the hometown.

For example, if your data file contains the following data:

John Seattle

William Yakima

Susan Yakima

Jack Lapush

Jennifer Seattle

Kim Seattle

Your program should produce the following output (Bold is user input):

What is the file name? home.txt

Seattle students: 3

John

Jennifer

Kim

Yakima students: 2

William

Susan

Lapush students: 1

Jack

Explanation / Answer

Java program

import java.io.File;

import java.io.FileNotFoundException;

import java.util.ArrayList;

import java.util.LinkedHashMap;

import java.util.List;

import java.util.Map;

import java.util.Scanner;

public class SampleTest {

          public static void main(String[] args) throws FileNotFoundException {

//Scanner used to take data from file

                   Scanner sc = new Scanner(new File("D://testdata//SampleData.txt"));

//Take a LinkedHashMap of type key as CityName and value as list of Student Names

LinkedHashMap<String, List<String>> hm =

new   LinkedHashMap<String, List<String>>();

//hasNext() is a method in scanner class used to check whether there is next token or not

                   while(sc.hasNext())

                   {

//nextLine() is a method returns the current line

//split() is a method used to split a string of space delimiter

                             String arr[]= sc.nextLine().split(" ");

//List is used to collect the Student Names

                                      List<String> li = new ArrayList<String>();

//containsKey() is a method used to check on a map whether it has key or not

//Here key is City Name

                                      if(hm.containsKey(arr[1]))

                                      {

//get() is method used to return the current value of specified key

                                                li=hm.get(arr[1]);

//add() is a method in the list used to add Student Name into List

                                                li.add(arr[0]);

                                      }

                                      else

                                      {

                                                li.add(arr[0]);

                                      }

//put() is a method in the map used to put data on the map of key CityName and value

//as List of StudentNames

                                      hm.put(arr[1], li);

                   }

//entrySet() is a method in map which return each Entry<Key,Value>

                   for(Map.Entry<String, List<String>> en:hm.entrySet())

                   {

//getKey() is a method used to getKey in Entry here key is CityName

//getValue() is a method used to getValue in Entry here value is List of Student Names

//size() is a method used to calculate no. of items in List

          System.out.println(en.getKey()+" Students: "+en.getValue().size());

                             for(String name:en.getValue())

                                      System.out.println(name);

                   }

          }

}

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