Substring in Java — Java Technical Interview Questions & Answers

Substring in Java

Substring in Java

  • Substring is about working with text in Java. Remember the base rule first: String is immutable. Compare content with equals, not ==.
  • For Substring, common APIs from memory: length(), charAt(i), substring(start, end), contains, equalsIgnoreCase, toUpperCase. Index starts at 0.
  • If Substring is StringBuilder/StringBuffer, you change text in place with append. If it is comparison, show == false and equals true for two new String("Hi").
  • For Substring, say the output before you code. Off-by-one on substring is a common trap (end index is exclusive).
  • Let's take this on the board with one tiny Main class — no extra files. Substring in Java — 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 Substring.

Technical Interview Tip: == vs equals() on String is a classic trap.

Code Examples for Substring in Java

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"));
  }
}

Substring in Java — shows length, substring, case change, and equalsIgnoreCase.

How to Explain Substring in Java to an Interviewer

What is Substring?

Substring works with Java text. String itself is immutable. Substring — compare content with equals, not ==. Substring — length, charAt, substring. substring end index is exclusive.

Why do we use Substring in Java?

Makes the program clearer or safer Substring works with Java text. String itself is immutable.

Write one small example of Substring.

Show syntax Say what prints

What mistake do beginners make with Substring?

Only the name, no example Substring — == compares references. User input almost never matches with ==.

Where is Substring used in a real program?

Day-to-day Java code