Java · Theory

How to read file line by line in Java?

Theory

171/270

How to read file line by line in Java?

How to read file line by line ? 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 How to read file line by line ?, always close resources. Prefer try-with-resources so close happens even if an error occurs. Buffered streams are faster for many small reads.

How to read file line by line ? 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. How to read file line by line 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 How to read file line by line ?.

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());
    }
  }
}

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

Short notes

DefHow to read file line by line ? — I/O = read/write outside the program (file, bytes, text).
RuleHow to read file line by line ? — byte streams for bytes, Reader/Writer for text, close with try-with-resources.
RememberHow to read file line by line ? — buffered streams are faster for many small reads.
TrapHow to read file line by line ? — 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()); } } }

How to read file line by line in Java?

Example

Short notes

Questions

How to read file line by line in Java?

Example

Short notes

Questions