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File Handling in Java

Theory

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File Handling in Java

File Handling is about reading or writing data outside the program — files, bytes, or characters. Byte streams (InputStream/OutputStream) handle raw bytes. Character streams (Reader/Writer) handle text.

For File Handling, always close resources. Prefer try-with-resources so close happens even if an error occurs. Buffered streams are faster for many small reads.

File Handling viva: serialization turns an object into bytes. transient fields are skipped. Don’t serialize secrets without a plan.

Let's take this on the board with one tiny Main class — no extra files. File Handling in Java — output: Hello File. StringReader → StringWriter is the same read/write pattern as a real file, and this Main always runs. Start from main, go line by line, and stop at each print. That output is the proof for File Handling.

Exam tip

Always mention closing resources in I/O answers.

Example

import java.io.*;
public class Main {
  public static void main(String[] args) throws Exception {
    String text = "Hello File";
    try (StringReader in = new StringReader(text);
         StringWriter out = new StringWriter()) {
      int ch;
      while ((ch = in.read()) != -1) out.write(ch);
      System.out.println(out.toString());
    }
  }
}

File Handling in Java — output: Hello File. StringReader → StringWriter is the same read/write pattern as a real file, and this Main always runs.

Short notes

DefFile Handling — I/O = read/write outside the program (file, bytes, text).
RuleFile Handling — byte streams for bytes, Reader/Writer for text, close with try-with-resources.
RememberFile Handling — buffered streams are faster for many small reads.
TrapFile Handling — forgetting to close, or serializing secrets.

import java.io.*; public class Main { public static void main(String[] args) throws Exception { String text = "Hello File"; try (StringReader in = new StringReader(text); StringWriter out = new StringWriter()) { int ch; while ((ch = in.read()) != -1) out.write(ch); System.out.println(out.toString()); } } }

File Handling in Java

Example

Short notes

Questions

File Handling in Java

Example

Short notes

Questions