Question

QUESTION

The ReadFile class opens and reads a text file. The WriteFile class opens and writes to a file. Compile and run these programs.

There are several ways to read/write text files. The examples shown here are just one way of achieving this.

Look at the API for the BufferedReader class. The readline() method is a simple way to read the text file line by line. It returns null when the end of the file has been reached.

https://docs.oracle.com/javase/8/docs/api/java/io/BufferedReader.html

Look at the API for the PrintWriter class. Notice that we can print to a file just like we print to the terminal. There are overloaded print() and println() methods that print with or without adding a newline.

https://docs.oracle.com/javase/8/docs/api/java/io/PrintWriter.html

Using the ReadFile and WriteFile classes as a starting point, write a program in a file called Frequent.java, that reads all the contents of a file (the provided text.txt, for example) and finds the 10 most frequently used words.

Your program will read every line in the input file and record each word in the line. A word is a sequence of consecutive non-whitespace characters.

Note that the split() method in the String class will break up a string into words.

 String s = "the cat in the     hat   .";
 String[] words = s.split("\\s+");

Here, the input "\\s+" tell split() to split the string s by whitespace characters.

Use a dictionary (HashMap) to store the words. The keys should be your words and the values should be the frequency count. Each time you see a word that you have already seen, you will need to update the value for that work (that key).

How do you use a HashMap? The API gives you lots of information!

https://docs.oracle.com/javase/8/docs/api/java/util/Hashtable.html

Once you have built your dictionary, you will need to extract all the key value pairs. You can, for example, use the keySet() method to obtain a set (use a Set for this; if you try to use HashSet you'll run into problems) of all the keys in the dictionary. You can then use this set to build list (ArrayList) of key-value pairs. You can use the helper class KeyValue for this if you wish. You can then sort the list using Collections.sort() since KeyValue implements comparable.

Once you have sorted the list, you write the last 10 (the 10 with the highest frequency) to a file called "best10.txt".

Note: Java provided a Map.Entry interface to help do this same thing (in place of the KeyValue class). Feel free to use this other approach for this problem.

package comp1406t5;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.PrintWriter;
import java.io.FileWriter;

public class WriteFile {

public static String filename = "output.txt";

public static void main(String[] args) {
try {
PrintWriter out;

// open file for writing
// (deleting current contents if the file already exists)
out = new PrintWriter(new FileWriter(filename));

// write to the file
for(int i=0; i<10; i+=1){
for(int j=0; j<20; j+=1){
if( Math.random() < 0.5 ){
out.print("/");
}else{
out.print("\\");
}
}
out.println();
}

// close the file
out.close();

} catch (FileNotFoundException e) {
System.out.println("Error: Cannot open file \"" + filename + "\" for writing.");
} catch (IOException e) {
System.out.println("Error: Cannot write to file \"" + filename + "\".");
}
}

}

package comp1406t5;

import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.FileReader;

public class ReadFile {

public static String filename = "input.txt";

public static void main(String args[]) {
try {

BufferedReader in;

// open file
in = new BufferedReader(new FileReader(filename));

// read from file
String line = in.readLine();
while( line != null ){
System.out.println(line);
line = in.readLine();
}

// clse file
in.close();

} catch (FileNotFoundException e) {
System.out.println("Error: Cannot open file \"" + filename + "\" for reading");
} catch (IOException e) {
System.out.println("Error: Cannot read from file \"" + filename + "\"");
}
}
}

package comp1406t5;

public class KeyValue implements Comparable<KeyValue>{
public String key;
public Integer value;

public KeyValue(String k, Integer v){
key = k;
value = v;
}

@Override
public int compareTo(KeyValue other){
return value.compareTo(other.value);
}
@Override
public String toString(){
return key + ":" + value;
}
}

Answer 1

2* import java.io. BufferedReader; 10 11 public class Most FrequentWords { static Map<String, Integer> map = new HashMap<String, Integer>(; 12 static void readFile(String fileName) throws IOException { BufferedReader reader = new BufferedReader(new FileReader(fileName)); String line; Enter file path : war_and_peace.txt the 4891 3109 2865 2277 1738 1604 1290 his 1237 in 1180 891 that while ((line = reader.readLine()) != null) { // remove punctuation String tokens[] = line.replaceAll("[^a-zA-Z ]",""). to LowerCase().split("\\s+"); for(String token: tokens) { token = token.trim(); map.put(token, map.getOrDefault(token, 6) + 1); reader.close(); public static void main(String[] args) throws IOException { Scanner user Input = new Scanner(System.in); System.out.print("Enter file path: "); String fileName = user Input.next(); // read file and populate hashmap readFile(fileName); 400 ArrayList<String> keys = new ArrayList<>(map.keySet(); keys. sort(new Comparator<String>() { @Override public int compare(String key1, String key2) { return map.get(key2) - map.get(key1); }); int i = 0; for(String key: keys) { if(i == 10) {

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class MostFrequentWords {
        static Map<String, Integer> map = new HashMap<String, Integer>(); 
        
        static void readFile(String fileName) throws IOException {
                BufferedReader reader = new BufferedReader(new FileReader(fileName));
                String line;

                while ((line = reader.readLine()) != null) {
                        // remove punctuation
                        String tokens[] = line.replaceAll("[^a-zA-Z ]", "").toLowerCase().split("\\s+");
                        for(String token: tokens) {
                                token = token.trim();
                                map.put(token, map.getOrDefault(token, 0) + 1);
                        }
                }

                reader.close();
        }

        public static void main(String[] args) throws IOException {
                Scanner userInput = new Scanner(System.in);
                System.out.print("Enter file path : ");
                String fileName = userInput.next();
                
                // read file and populate hashmap
                readFile(fileName);
                
                ArrayList<String> keys = new ArrayList<>(map.keySet());
                keys.sort(new Comparator<String>() {
                        @Override
                        public int compare(String key1, String key2) {
                                return map.get(key2) - map.get(key1);
                        }
                        
                });
                
                int i = 0;
                for(String key: keys) {
                        if(i == 10) {
                                break;
                        }
                        Integer count = map.get(key);
                        System.out.println(String.format("%-20s%d", key, count));
                        i++;
                }
                
                // close scanner
                userInput.close();
        }

}

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