Java Text File Handling: Write, Append, Read and Process (ISC Class 11)

Understand Text Files in Java: Create, Write, Append, Read, Search and Count

import java.io.*;
FileWriter fw = new FileWriter("data.txt");          // creates or overwrites
fw.write("Java is fun");
fw.write("\n");                                      // new line
fw.close();                                           // always close
FileWriter fa = new FileWriter("data.txt", true);     // append mode

BufferedReader br = new BufferedReader(new FileReader("data.txt"));
String line;
while ((line = br.readLine()) != null) {
    System.out.println(line);
}
br.close();

Text Files in Java: Create, Write, Append, Read, Search and Count: key facts

Write and read classes

FileWriter	write
FileReader	read characters
BufferedReader	readLine

java.io package.

End of file

readLine() returns null | read() returns -1

Loop condition.

Modes

new FileWriter(name): overwrite | new FileWriter(name, true): append

Constructor argument.

How to answer Text Files in Java: Create, Write, Append, Read, Search and Count questions

1. 1Import java.io and handle IOException.
2. 2Open the file (reader or writer).
3. 3Loop with readLine() until null, updating counters.
4. 4Close the file and print the results.

Text Files in Java: Create, Write, Append, Read, Search and Count in real life

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

Tricks to remember Text Files in Java: Create, Write, Append, Read, Search and Count

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

• null ends the line loop

  readLine() returns null at end.

  Use it when: Read loop.

• true appends

  Second argument true keeps old contents.

  Use it when: Append.

• Close it

  Close writers so data are saved.

  Use it when: Closing.

Text Files in Java: Create, Write, Append, Read, Search and Count: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

BufferedReader br = new BufferedReader(new FileReader("data.txt"));
String line;
int lines = 0, words = 0, chars = 0;
while ((line = br.readLine()) != null) {
    lines++;
    words += new StringTokenizer(line).countTokens();
    chars += line.length();
}
br.close();
System.out.println(lines + " " + words + " " + chars);

int sum = 0, max = Integer.MIN_VALUE, n = 0;
while ((line = br.readLine()) != null) {
    int x = Integer.parseInt(line.trim());
    sum += x; n++;
    if (x > max) max = x;
}
System.out.println(sum + " " + max + " " + (double) sum / n);

Where students lose marks in Text Files in Java: Create, Write, Append, Read, Search and Count

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

• ✗Mistake: Forgetting IOException

  File operations can fail.

  Wrong working

  No try-catch or throws

  Right working

  throws IOException

  ✓Do this: Declare or handle it.

  Usually costs: 1-2 marks.

• ✗Mistake: Looping with while (br.readLine() != null) then using readLine() again

  Skipping a line.

  Wrong working

  Two readLine() calls

  Right working

  while ((line = br.readLine()) != null)

  ✓Do this: Store the line in the loop condition.

  Usually costs: 2 marks.

• ✗Mistake: Not closing the file

  Data may not be saved.

  Wrong working

  No close()

  Right working

  br.close() / fw.close()

  ✓Do this: Close in the end.

  Usually costs: 1 mark.

Practice questions on Text Files in Java: Create, Write, Append, Read, Search and Count

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 · MCQBoard level

   In a read loop, readLine() returns which value at the end of the file?
   (a) -1 (b) "" (c) null (d) 0

   Hint

   A reference value.

   Answer

   (c) null

2. Q2 · 3 marks · Short answerBoard level

   Write a code segment to create a file "names.txt" and store the three names Asha, Bilal and Chitra, one per line. (3 marks)

   Hint

   PrintWriter or FileWriter.

   Answer

   PrintWriter pw = new PrintWriter(new FileWriter("names.txt")); pw.println("Asha"); pw.println("Bilal"); pw.println("Chitra"); pw.close(); (inside a method that handles IOException).

3. Q3 · 5 marks · Long answerHarder board level

   A file holds words, one per line: apple, kiwi, banana, fig, grape. Write a segment that prints the longest word and the number of words that have more than 4 letters, and state the output. (5 marks)

   Hint

   Lengths 5, 4, 6, 3, 5.

   Answer

   Track the longest while reading with line.length(). Output: banana 3 (apple 5, banana 6 and grape 5 have more than 4 letters; kiwi has 4 and fig has 3).

4. Q4 · 5 marks · Long answerHarder board level

   A file "temp.txt" has the readings 21, 25, 18, 30, 26. Write a segment that finds and prints how many readings are above the average and the average. State the output. (5 marks)

   Hint

   Sum = 120.

   Answer

   Read all values into an array (or read the file twice). Sum = 120; average = 24.0. Readings above 24: 25, 30, 26 = 3. Output: 3 24.0

5. Q5 · 3 marks · Short answerHOTS / competency

   A program appends a record to a file but each run shows only the latest record in the file. Another reads the file and prints one line less than it holds. Identify the likely cause of each. (3 marks)

   Hint

   Mode and loop.

   Answer

   The first program uses the default overwrite mode instead of append (new FileWriter(name, true)). The second calls readLine() twice per iteration (once in the loop condition and again inside), skipping a line.

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.Class for appending text?Show answer

   FileWriter with true.

2. 2.readLine() at end?Show answer

   Returns null.

3. 3.Which exception?Show answer

   IOException.

4. 4.Count words with?Show answer

   StringTokenizer countTokens().

5. 5.Why close a file?Show answer

   To save data and release it.

Text Files in Java: Create, Write, Append, Read, Search and Count: frequently asked questions