Question

1. Read previously created binary file using ObjectInputStream
2. Create an appropriate instance of HashMap from Java library
3. Populate the HashMap with data from binary file
4. Display the information read in a user friendly format

Problem:

Given: Words.dat – a binary file consisting of all the words in War and Peace

Goal: Read the words in from the binary file and figure out how many times each word appears in the file. Display the results to the user.

Use a HashMap with the word as a key (String) and an Integer as the value.   For each word, first check to see if it already exists in the Map. If not, add the word as key with a value of 1 for the Integer value.

If it does, get the current value and increment by 1 – replace the old key,value with the new key, value.

After all the words are processed and the HashMap is complete. Iterate through the Hash map and display the results in a user -friendly fashion. Tell me which option you chose in the Assignment box when you submit the homework

Display Options: (Choose one not all)

1. Create an easy to read table and print to the console. Hint: Use tabs (/t) (values are not from file)

Example:

Word                     Count

A                             190

Apple                    6

Etc

2. Display on a Java FX Gui – use ListView for the Words and click to see count

C. Create a text file with the data formatted similar to the console

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.ObjectOutputStream;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.Scanner;
import java.util.Set;

/**
* This file is intended to show how the binary file words.dat was created

*This is not intended to be used only to
* demonstrate how the file was written so it can be read properly

*cjohns25
*/
public class CreateBinaryFile
{

   public static void main(String[] args)
   {
       // step 1 - read in all the words from war and peace into an arrayList
       ArrayList words = new ArrayList();
       Scanner in;
       try
       {
           in = new Scanner(new File("war-and-peace.txt"));

           // Use any characters other than a-z or A-Z as delimiters
           in.useDelimiter("[^a-zA-Z]+");
           while (in.hasNext())
           {
               words.add(in.next().toLowerCase());
           }
           in.close();
       } catch (FileNotFoundException e)
       {
           // TODO Auto-generated catch block
           e.printStackTrace();
       }

       // write to words.dat in binary format
       // open a binary file with ObjectOutputStream for writing
       try
       {
           // Create an output stream for file words.data
           ObjectOutputStream output = new ObjectOutputStream(new FileOutputStream("words.dat", true));

           // Write arrayList to the object output stream one string at a time
           for (String w : words)
           {
               output.writeObject(w);
           }

           output.close();

       } catch (Exception e)
       {
           e.printStackTrace(); // provide this to see where problem occurred
           System.out.println("Problem encountered writing file"); // provide this for user
       }

   }
}

*My CODE*

import java.io.FileInputStream;
import java.io.ObjectInputStream;
import java.util.HashMap;

public class HashMapWords {
public static void main(String[] args) throws Exception {

HashMap<String, Integer> map = new HashMap<String, Integer>();
try (ObjectInputStream datFile = new ObjectInputStream(new FileInputStream("words.dat"))) {

while (true) {
try {
String key = datFile.readUTF();
if (!map.containsKey(key)) {
map.put(key, 0);
}
map.put(key, map.get(key) + 1);
} catch (Exception ex) {
break;
}
}
}

System.out.println("Word\t\tCount");

for (String key : map.keySet()) {
System.out.println(key + "\t\t" + map.get(key));
}
}

}

*OUTPUT*

Word Count

*HAVING TROUBLE MAKING THIS WORK REALLY NEED SOME HELP, TELL ME WHAT IM DOING WRONG. THANK YOU FOR THE HELP *

Answer 1

The error was on only one line namely ==> String key = datFile.readUTF();==> this doesnot work because UTF-8 is a text to binary encoding which means conversion of text to binary will succeed ...but conversion from binary to string may fail ...So UTF function will not be used here ...Now since Object is being written in binary file ...So use readObject function to read the object and typecast it with String object...

i.e    String key = (String)datFile.readObject(); //read objects from binary file and typecast to required Object

Attaching the code snippet and screenshot ..

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package hashmapwords;

/**
 *
 * @author vijay
 */
import java.io.FileInputStream;
import java.io.ObjectInputStream;
import java.util.HashMap;


public class HashMapWords {
public static void main(String[] args) throws Exception {

HashMap<String, Integer> map = new HashMap<String, Integer>();
try (ObjectInputStream datFile = new ObjectInputStream(new FileInputStream("words.dat"))) {

while (true) {
try {
    String key = (String)datFile.readObject(); //read objects from binary file and typecast to required Object 

if (!map.containsKey(key)) {
map.put(key, 0);
}
map.put(key, map.get(key) + 1);
} catch (Exception ex) {
break;
}
}
}

System.out.println("Word\t\tCount");

for (String key : map.keySet()) {
System.out.println(key + "\t\t" + map.get(key));
}
}

}

Screenshots ==>input.txt is the file which was converted to binary format file words.dat