Java · Theory

StringWriter

Theory

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StringWriter

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

StringWriter 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. StringWriter — shows length, substring, case change, and equalsIgnoreCase. Start from main, go line by line, and stop at each print. That output is the proof for StringWriter.

Exam tip

== vs equals() on String is a classic trap.

Example

// String methods
public class Main {
  public static void main(String[] args) {
    String s = "PrepPilot";
    System.out.println(s.length());
    System.out.println(s.substring(0, 4));
    System.out.println(s.toUpperCase());
    System.out.println("prep".equalsIgnoreCase("PREP"));
  }
}

StringWriter — shows length, substring, case change, and equalsIgnoreCase.

Short notes

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

// String methods public class Main { public static void main(String[] args) { String s = "PrepPilot"; System.out.println(s.length()); System.out.println(s.substring(0, 4)); System.out.println(s.toUpperCase()); System.out.println("prep".equalsIgnoreCase("PREP")); } }

StringWriter

Example

Short notes

Questions

StringWriter

Example

Short notes

Questions