How to tokenize an input file in java

i'm doing tokenizing a text file in java. I want to read an input file, tokenize it and write a certain character that has been tokenized into an output file. This is what i've done so far:

package org.apache.lucene.analysis;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.StreamTokenizer;

class StringProcessing {
    // Create BufferedReader class instance
    public static void main(String[] args) throws IOException {
        InputStreamReader input = new InputStreamReader(System.in);
        BufferedReader keyboardInput = new BufferedReader(input);
        System.out.print("Please enter a java file name: ");
        String filename = keyboardInput.readLine();
        if (!filename.endsWith(".DAT")) {
            System.out.println("This is not a DAT file.");
            System.exit(0);
        }
        File File = new File(filename);
        if (File.exists()) {
            FileReader file = new FileReader(filename);
            StreamTokenizer streamTokenizer = new StreamTokenizer(file);
            int i = 0;
            int numberOfTokensGenerated = 0;
            while (i != StreamTokenizer.TT_EOF) {
                i = streamTokenizer.nextToken();
                numberOfTokensGenerated++;
            }
            // Output number of characters in the line
            System.out.println("Number of tokens = " + numberOfTokensGenerated);
            // Output tokens
            for (int counter = 0; counter < numberOfTokensGenerated; counter++) {
                char character = file.toString().charAt(counter);
                if (character == ' ') { System.out.println(); } else { System.out.print(character); }
            }
        } else {
            System.out.println("File does not exist!");
            System.exit(0);
        }

        System.out.println("\n");
    }//end main
}//end class

When i run this code, this is what i get:

Please enter a java file name: D://eclipse-java-helios-SR1-win32/LexractData.DAT Number of tokens = 129 java.io.FileReader@19821fException in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 25 at java.lang.String.charAt(Unknown Source) at org.apache.lucene.analysis.StringProcessing.main(StringProcessing.java:40)

The input file will look like this:开发者_运维问答

-K1 Account 
--Op1 withdraw
---Param1 an
----Type Int
---Param2 amount
----Type Int
--Op2 deposit
---Param1 an
----Type Int
---Param2 Amount
----Type Int
--CA1 acNo
---Type Int
-K2 CheckAccount 
--SC Account
--CA1 credit_limit
---Type Int
-K3 Customer
--CA1 name
---Type String
-K4 Transaction
--CA1 date
---Type Date
--CA2 time
---Type Time
-K5 CheckBook
-K6 Check
-K7 BalanceAccount
--SC Account

I just want to read the string which are starts with -K1, -K2, -K3, and so on... can anyone help me?

The problem is with this line --

char character = file.toString().charAt(counter);

file is a reference to a FileReader that does not implement toString() .. it calls Object.toString() which prints a reference around 25 characters long. Thats why your exception says OutofBoundsException at the 26th character.

To read the file correctly, you should wrap your filereader with a bufferedreader and then put each readline into a stringbuffer.

FileReader fr = new FileReader(filename);
BufferedReader br = new BufferedReader(fr);
StringBuilder sb  = new StringBuilder();
String s;
while((s = br.readLine()) != null) {
sb.append(s);
} 

// Now use sb.toString() instead of file.toString()

If you are wanting to tokenize the input file then the obvious choice is to use a Scanner. The Scanner class reads a given input stream, and can output either tokens or other scanned types (scanner.nextInt(), scanner.nextLine(), etc).

import java.util.Scanner;
import java.io.File;
import java.io.IOException;
public static void main(String[] args) throws IOException {
    Scanner in = new Scanner(new File("filename.dat"));
    while (in.hasNext) {
        String s = in.next(); //get the next token in the file
        // Now s contains a token from the file
    }
}

Check out Oracle's documentation of the Scanner class for more info.

public class FileTokenize { public static void main(String[] args) throws IOException {

    final var lines = Files.readAllLines(Path.of("myfile.txt"));
    FileWriter writer = new FileWriter( "output.txt");
    String data = " ";

    for (int i = 0; i < lines.size(); i++) {
        data = lines.get(i);
        StringTokenizer token = new StringTokenizer(data);
        while (token.hasMoreElements()) {
            writer.write(token.nextToken() + "\n");
        }
    }
    writer.close();
}