Basic Input/Output and Text File Handling in Java: ISC 11

What Basic Input/Output and Text File Handling is about

Weightage: Basic Input/Output and Text File Handling is topic 11 of the ISC Class XI Computer Science syllabus, in Section B - Java. CISCE weights Section B at 30 of the 70 marks in Paper I (Theory). Class XI is examined by the school, so your school sets the paper within this weightage.Source: CISCE ISC Computer Science syllabus, examination year 2028, Class XI unit weightage

Key concepts

Streams, tokens and whitespace

A stream is a sequence of data flowing between a program and a source or destination.

• Input stream: data flows into the program (keyboard: System.in; a file).
• Output stream: data flows out of the program (screen: System.out; a file).
• Byte streams handle raw bytes; character streams (Reader and Writer classes such as FileReader and FileWriter) handle text as Unicode characters.

A token is a meaningful unit of input (a word or a number) separated from others by delimiters. By default the delimiter is whitespace: spaces, tabs (\t) and line breaks (\n). Multiple whitespace characters together count as one separator.

In the input line ' Java is fun ', there are 3 tokens: Java, is and fun.

User-defined delimiters let other characters separate tokens: commas in '82,75,91', slashes in a date '12/05/2026', colons in a time '10:20:30'.

Worked example

How many tokens are in 'I love Java programming' with whitespace delimiters, and in 'a,b,,c' with ',' as the delimiter? [1 mark]

Try it first, then show the solutionSolution

1. Whitespace: I, love, Java, programming = 4 (the double space is one separator).
2. Comma: a, b, c = 3 (empty tokens between two commas are skipped by StringTokenizer).

Answer: 4 and 3.

The Scanner class for input of various types

Scanner (java.util) reads tokens from an input source and converts them to the required type.

Scanner sc = new Scanner(System.in);

Method	Reads
nextInt(), nextLong(), nextDouble(), nextFloat(), nextBoolean()	the next token as that type
next()	the next token as a String (one word)
nextLine()	the rest of the current line, including spaces
next().charAt(0)	a single character
hasNextInt(), hasNext(), hasNextLine()	true if such input is available (without reading it)

The nextLine trap: after nextInt() or nextDouble(), the line break is still waiting; a following nextLine() returns an empty string. Call an extra sc.nextLine() to consume it first.

InputMismatchException is thrown when the token does not match the requested type (typing 'ninety' for nextInt()). Catch it, then skip the bad token with next().

// Reading different types with Scanner, and handling a wrong input type.
import java.util.Scanner;
import java.util.InputMismatchException;

public class ScannerDemo
{
    public static void main(String[] args)
    {
        Scanner sc = new Scanner(System.in);
        String name = sc.next();               // one token (stops at whitespace)
        int age = sc.nextInt();
        double height = sc.nextDouble();
        sc.nextLine();                         // consume the rest of the line
        String city = sc.nextLine();           // whole line, spaces included
        System.out.println("name = " + name + ", age = " + age + ", height = " + height);
        System.out.println("city = " + city);

        try
        {
            int marks = sc.nextInt();          // the next token is 'ninety': not an int
            System.out.println("marks = " + marks);
        }
        catch (InputMismatchException e)
        {
            System.out.println("Not a whole number: " + sc.next());   // read and skip the bad token
        }

        int sum = 0, count = 0;
        while (sc.hasNextInt())                // read numbers until a non-number appears
        {
            sum += sc.nextInt();
            count++;
        }
        System.out.println("read " + count + " numbers, sum = " + sum);
    }
}

Input:

Riya 16 1.62
New Delhi
ninety
12 7 30 end

Output:

name = Riya, age = 16, height = 1.62
city = New Delhi
Not a whole number: ninety
read 3 numbers, sum = 49

Worked example

For the input '5 apples 3.5' followed by a new line 'next line', what do nextInt(), next(), nextDouble(), nextLine() and another nextLine() return? [2 marks]

Try it first, then show the solutionSolution

1. nextInt() → 5; next() → "apples"; nextDouble() → 3.5.
2. nextLine() → "" (the rest of line 1 is empty); the second nextLine() → "next line".

Answer: 5, "apples", 3.5, "" and "next line".

StringTokenizer and user-defined delimiters

StringTokenizer (java.util) breaks a String into tokens.

• new StringTokenizer(str): delimiters are whitespace.
• new StringTokenizer(str, delims): every character in delims is a delimiter (",;" means comma or semicolon).
• new StringTokenizer(str, delims, true): the delimiters are also returned as tokens.

Methods: countTokens() (tokens remaining), hasMoreTokens() (any left?), nextToken() (the next token as a String).

Scanner with a user-defined delimiter: sc.useDelimiter("/") makes Scanner split on slashes, so a date can be read with nextInt() three times.

Tokens are Strings; convert numbers with Integer.parseInt or Double.parseDouble.

// Tokens and delimiters: StringTokenizer with default and user-defined delimiters,
// and Scanner with a user-defined delimiter.
import java.util.StringTokenizer;
import java.util.Scanner;

public class Tokens
{
    public static void main(String[] args)
    {
        String line = "  Java  is   fun ";
        StringTokenizer st = new StringTokenizer(line);          // whitespace is the delimiter
        System.out.println("tokens = " + st.countTokens());
        while (st.hasMoreTokens())
            System.out.print("[" + st.nextToken() + "]");
        System.out.println();

        String csv = "Asha,82,Mumbai;Bilal,75,Pune";
        StringTokenizer rec = new StringTokenizer(csv, ",;");   // user-defined delimiters
        while (rec.hasMoreTokens())
            System.out.print(rec.nextToken() + " | ");
        System.out.println();

        StringTokenizer withDelims = new StringTokenizer("3+4-2", "+-", true);   // return delimiters too
        while (withDelims.hasMoreTokens())
            System.out.print("<" + withDelims.nextToken() + ">");
        System.out.println();

        Scanner sc = new Scanner("12/05/2026");
        sc.useDelimiter("/");                                    // Scanner with a user-defined delimiter
        int d = sc.nextInt(), m = sc.nextInt(), y = sc.nextInt();
        System.out.println("day " + d + ", month " + m + ", year " + y);
    }
}

Output:

tokens = 3
[Java][is][fun]
Asha | 82 | Mumbai | Bilal | 75 | Pune | 
<3><+><4><-><2>
day 12, month 5, year 2026

Worked example

Using StringTokenizer with ':' as delimiter, convert the time '12:45:30' into seconds. [2 marks]

Try it first, then show the solutionSolution

1. Tokens 12, 45, 30 → parseInt each.
2. 12 × 3600 + 45 × 60 + 30 = 43,200 + 2,700 + 30 = 45,930.

Answer: 45,930 seconds.

Need for data files; input/output exceptions

Why data files:

1. Permanent storage: variables are lost when the program ends; files keep data between runs.
2. Large data: thousands of records need not be typed each time.
3. Sharing: other programs (or people) can use the same data.
4. Records: marks, stock or attendance can be added over time.

Text files store data as readable characters (lines of text), which can be opened in any editor; the syllabus uses text files only.

Input/output exceptions: file operations can fail at run time: the file may not exist, the disk may be full, or permission may be denied. Java reports these with IOException (java.io), a checked exception: code that opens, reads or writes files must either catch it (try-catch) or declare it (throws IOException). FileNotFoundException is a kind of IOException.

Closing: always close() a file when finished (ideally in finally) so that data is written out (flushed) and the file is released.

Worked example

Why must a method that uses FileReader either catch IOException or declare throws IOException? [1 mark]

Try it first, then show the solutionSolution

1. IOException is a checked exception; the compiler insists that it be handled or declared.

Answer: Because IOException is checked: without a catch or a throws clause, the program does not compile.

Text files: create, write, append, read, search

Writing (output stream):

• Create and write: FileWriter fw = new FileWriter("marks.txt"); fw.write("Asha 82\n"); fw.close(); creates the file, or overwrites it if it exists.
• Append: new FileWriter("marks.txt", true) adds to the end instead of overwriting.

Reading (input stream): wrap FileReader in BufferedReader to read whole lines:

BufferedReader br = new BufferedReader(new FileReader("marks.txt"));

readLine() returns the next line, or null at the end of the file; loop with while ((line = br.readLine()) != null).

Searching: read line by line and compare (equals, startsWith, indexOf); stop with break when found; report 'not found' after the loop.

// Text file handling with character streams: create and write, append, read, and search.
import java.io.FileWriter;
import java.io.FileReader;
import java.io.BufferedReader;
import java.io.IOException;

public class TextFile
{
    static final String FILE = "marks.txt";

    static void create() throws IOException
    {
        FileWriter fw = new FileWriter(FILE);           // creates (or overwrites) the file
        fw.write("Asha 82\n");
        fw.write("Bilal 75\n");
        fw.write("Chitra 91\n");
        fw.close();                                     // flushes and releases the file
    }

    static void append(String record) throws IOException
    {
        FileWriter fw = new FileWriter(FILE, true);     // true = append mode
        fw.write(record + "\n");
        fw.close();
    }

    static void display() throws IOException
    {
        BufferedReader br = new BufferedReader(new FileReader(FILE));
        String line;
        int n = 0, total = 0;
        while ((line = br.readLine()) != null)          // null means end of file
        {
            System.out.println("  " + line);
            total += Integer.parseInt(line.substring(line.indexOf(' ') + 1));
            n++;
        }
        br.close();
        System.out.println("  " + n + " records, average = " + (double) total / n);
    }

    static String search(String name) throws IOException
    {
        BufferedReader br = new BufferedReader(new FileReader(FILE));
        String line, result = name + " not found";
        while ((line = br.readLine()) != null)
        {
            if (line.startsWith(name + " "))
            {
                result = "found: " + line;
                break;
            }
        }
        br.close();
        return result;
    }

    public static void main(String[] args)
    {
        try
        {
            create();
            System.out.println("After creating:");
            display();
            append("Dev 68");
            System.out.println("After appending:");
            display();
            System.out.println(search("Chitra"));
            System.out.println(search("Esha"));
            BufferedReader br = new BufferedReader(new FileReader("missing.txt"));
        }
        catch (IOException e)
        {
            System.out.println("IOException: " + e.getMessage());
        }
    }
}

Output:

After creating:
  Asha 82
  Bilal 75
  Chitra 91
  3 records, average = 82.66666666666667
After appending:
  Asha 82
  Bilal 75
  Chitra 91
  Dev 68
  4 records, average = 79.0
found: Chitra 91
Esha not found
IOException: missing.txt (The system cannot find the file specified)

The last line shows the IOException caught when opening a file that does not exist (the exact message text depends on the operating system).

Worked example

A program writes 'one' to t.txt with new FileWriter("t.txt"), closes it, then writes 'two' with new FileWriter("t.txt") again. What does the file contain? How would you keep both lines? [2 marks]

Try it first, then show the solutionSolution

1. The second FileWriter without true overwrites the file: it contains only 'two'.
2. Use new FileWriter("t.txt", true) for the second write to append.

Answer: Only 'two'; open the second FileWriter in append mode (second argument true) to keep both.

Processing file data: counting and statistics

Most file questions combine reading with processing:

1. Read each line with readLine().
2. Split the line into tokens (StringTokenizer, or indexOf and substring).
3. Convert numbers with parseInt or parseDouble.
4. Update counters, totals, maximums or search results.
5. After the loop, close the file and print the results.

The program below writes three lines to notes.txt, then counts the lines, the words (using spaces, commas and full stops as delimiters) and the occurrences of 'water', ignoring case.

// Writes a short text file, then reads it back counting lines, words and occurrences of a word.
import java.io.*;
import java.util.StringTokenizer;

public class WordStats
{
    public static void main(String[] args)
    {
        String file = "notes.txt";
        try
        {
            FileWriter fw = new FileWriter(file);
            fw.write("The water cycle moves water around the Earth.\n");
            fw.write("Water evaporates, condenses and falls as rain.\n");
            fw.write("Rain water fills rivers.\n");
            fw.close();

            BufferedReader br = new BufferedReader(new FileReader(file));
            String line;
            int lines = 0, words = 0, hits = 0;
            while ((line = br.readLine()) != null)
            {
                lines++;
                StringTokenizer st = new StringTokenizer(line, " ,.");   // spaces and punctuation
                while (st.hasMoreTokens())
                {
                    String w = st.nextToken();
                    words++;
                    if (w.equalsIgnoreCase("water"))
                        hits++;
                }
            }
            br.close();
            System.out.println("lines = " + lines + ", words = " + words + ", 'water' = " + hits);
        }
        catch (IOException e)
        {
            System.out.println("File error: " + e.getMessage());
        }
    }
}

Output:

lines = 3, words = 19, 'water' = 4

Worked example

In WordStats, why are ',' and '.' included in the delimiters? [1 mark]

Try it first, then show the solutionSolution

1. Without them, 'Earth.' and 'evaporates,' would be tokens with punctuation attached and 'water.' would not match 'water'.

Answer: So that punctuation is not counted as part of words, and words such as 'Earth.' match cleanly.

Basic Input/Output and Text File Handling in real life

Each concept, met in an everyday situation. Read the situation, answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Topics in this chapter

• Streams, Tokens, the Scanner Class and StringTokenizer
• Text Files in Java: Create, Write, Append, Read, Search and Count

Basic Input/Output and Text File Handling: syntax and key facts

Scanner input

Scanner sc = new Scanner(System.in); int n = sc.nextInt(); String w = sc.next(); String line = sc.nextLine();

StringTokenizer

StringTokenizer st = new StringTokenizer(str, delims); while (st.hasMoreTokens()) st.nextToken();

Write or append

new FileWriter(name) overwrites; new FileWriter(name, true) appends

Read lines

BufferedReader br = new BufferedReader(new FileReader(name)); while ((line = br.readLine()) != null) { ... } br.close();

Exceptions

File code	try { ... } catch (IOException e) { ... }
Or	method ... throws IOException
Scanner type errors	InputMismatchException

Basic Input/Output and Text File Handling: diagrams to practise

Practise each one on paper: draw it from the checklist, then tick off every label.

How the school exam asks Basic Input/Output and Text File Handling

The question patterns to expect, and the method that works for each.

Tricks to remember Basic Input/Output and Text File Handling

Short memory aids. Say each one aloud once, then use it on a question the same day.

• next = word, nextLine = rest of line

  After nextInt, nextLine first eats the leftover line break.

  Use it when: Scanner input.

• has, then next

  hasNextInt() checks; nextInt() takes.

  Use it when: Safe input loops.

• null means the end

  readLine() returns null at end of file.

  Use it when: Reading files.

• Open, use, close

  Every FileWriter and BufferedReader needs close().

  Use it when: File handling.

Basic Input/Output and Text File Handling: exam-level solved questions

Ordered from exam level to HOTS. Cover the solution, write your own, then compare step by step.

Case-study practice (Section D style)

Read the situation, then answer every part. In a school exam set on the board pattern this is a 5-mark question split into 1 + 2 + 2 marks.

Where the marks are

How a typical answer is split into step marks. Show every step: a right final answer alone rarely earns full marks.

Where students lose marks in Basic Input/Output and Text File Handling

The slips examiners see most often, and what to write instead.

• ✗Mistake: Reading a line with nextLine right after nextInt

  It returns the empty rest of the previous line.

  ✓Do this: Add an extra sc.nextLine() to consume the line break.

  Usually costs: 1 mark.

• ✗Mistake: Forgetting append mode

  new FileWriter(name) erases the existing file.

  ✓Do this: Use new FileWriter(name, true) to add records.

  Usually costs: 1-2 marks.

• ✗Mistake: Not handling IOException

  It is a checked exception; the program will not compile.

  ✓Do this: try-catch (IOException e) or throws IOException.

  Usually costs: 1 mark.

• ✗Mistake: Forgetting to close the writer

  Buffered data may never reach the file.

  ✓Do this: Call close() (in finally where possible).

  Usually costs: 1 mark.

Practice questions on Basic Input/Output and Text File Handling

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

1. Q1 · 1 mark · MCQExam level

   Which method of BufferedReader returns null at the end of a file?
   (a) read()
   (b) readLine()
   (c) nextLine()
   (d) close()

   Hint

   Whole lines.

   Answer

   (b) readLine().

2. Q2 · 1 mark · Very short answerExam level

   Name the exception thrown when nextInt() reads 'abc'.

   Hint

   Mismatch.

   Answer

   InputMismatchException.

3. Q3 · 2 marks · Short answerExam level

   Distinguish between next() and nextLine() of Scanner.

   Hint

   Word vs line.

   Answer

   next() reads the next token (one word, stopping at whitespace). nextLine() reads the rest of the current line, including spaces, and consumes the line break.

4. Q4 · 1 mark · Very short answerHarder exam level

   How many tokens are in '10:20:30' with the default delimiters, and with ':' as the delimiter?

   Hint

   No whitespace inside.

   Answer

   1 with the default (whitespace) delimiters; 3 with ':'.

5. Q5 · 2 marks · Short answerHarder exam level

   Write a code segment that reads integers from a Scanner until a non-integer appears and prints their sum, and give the sum for the input '7 8 x 9'.

   Hint

   hasNextInt.

   Answer

   int sum = 0; while (sc.hasNextInt()) sum += sc.nextInt(); System.out.println(sum); For '7 8 x 9' it stops at x and prints 15.

6. Q6 · 2 marks · Short answerHarder exam level

   State four reasons for using data files.

   Hint

   Permanent, large, shared, growing.

   Answer

   Permanent storage beyond the program's run; handling large amounts of data without retyping; sharing data among programs and users; keeping growing records (appending over time).

7. Q7 · 5 marks · Short answerHOTS / competency

   Write a method void showAbove(String file, int cut) that reads lines 'name marks' and prints the names of students with marks above cut. What would it print for the marks file after appending (cut = 80)?

   Hint

   readLine, split at the space.

   Answer

   void showAbove(String file, int cut) throws IOException { BufferedReader br = new BufferedReader(new FileReader(file)); String line; while ((line = br.readLine()) != null) { int sp = line.indexOf(' '); int m = Integer.parseInt(line.substring(sp + 1)); if (m > cut) System.out.println(line.substring(0, sp)); } br.close(); } For Asha 82, Bilal 75, Chitra 91, Dev 68 and cut 80: Asha and Chitra.

8. Q8 · 2 marks · Short answerHarder exam level

   Explain the difference between an input stream and an output stream, and name the character-stream classes used for text files.

   Hint

   Direction.

   Answer

   An input stream carries data into the program from a source (keyboard, file); an output stream carries data from the program to a destination (screen, file). For text files: FileReader (often wrapped in BufferedReader) for input and FileWriter for output.

9. Q9 · 10 marks · Long answerHOTS / competency

   Write a program that stores 'name,phone' records in contacts.txt (creating it with three records), appends one more, and then searches for a name entered by the user, printing the phone number or 'not found'.

   Hint

   Methods for create, append, search.

   Answer

   create(): FileWriter fw = new FileWriter("contacts.txt"); write three lines such as "Asha,98100\n"; close. append(String rec): new FileWriter("contacts.txt", true); write rec + "\n"; close. search(String name): BufferedReader over FileReader; for each line, StringTokenizer st = new StringTokenizer(line, ","); String n = st.nextToken(), p = st.nextToken(); if (n.equalsIgnoreCase(name)) return p; after the loop return "not found"; close the reader. main(): call create and append, read the name with Scanner.nextLine(), print search(name); wrap in try-catch (IOException) to report file errors.

10. Q10 · 2 marks · Short answerHOTS / competency

    What does the file contain after: FileWriter fw = new FileWriter("t.txt"); fw.write("one\n"); fw.close(); fw = new FileWriter("t.txt"); fw.write("two\n"); fw.close(); and what do two readLine() calls return?

    Hint

    Overwrite.

    Answer

    Only 'two'. The first readLine() returns "two" and the second returns null (end of file).

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1. 1.Default delimiter?Show answer

   Whitespace.

2. 2.StringTokenizer methods?Show answer

   countTokens, hasMoreTokens, nextToken.

3. 3.Append to a file?Show answer

   new FileWriter(name, true).

4. 4.End of file for readLine?Show answer

   null.

5. 5.Checked exception for files?Show answer

   IOException.

6. 6.Set a Scanner delimiter?Show answer

   useDelimiter("...").

Quick revision checklist

The night before the exam: can you do each of these without looking?

• ☐Stream: input into the program, output out of it; character streams for text.
• ☐Token: unit between delimiters; default whitespace.
• ☐Scanner: nextInt, nextDouble, next, nextLine, hasNextInt; useDelimiter.
• ☐StringTokenizer(str, delims[, true]): countTokens, hasMoreTokens, nextToken.
• ☐FileWriter(name) overwrites; (name, true) appends; close().
• ☐BufferedReader(new FileReader(name)).readLine() until null; IOException must be handled.

Basic Input/Output and Text File Handling: frequently asked questions