StringBuilder Class Methods

StringBuilder Class Methods

1. Same as StringBuffer! (beginner relief)

Identical methods, identical results — only speed/threads differ (see prev topic). Learn once, use both! Master: append, insert, delete, reverse, replace, toString.

2. Code — Palindrome Checker (exam classic!)

public class Palin {
    static boolean isPalin(String s) {
        // StringBuilder reverse in ONE line!
        String rev = new StringBuilder(s).reverse().toString();
        return s.equals(rev); // content compare!
    }
    public static void main(String[] args) {
        System.out.println(isPalin("madam")); // true
        System.out.println(isPalin("hello")); // false
        // builder chain demo:
        StringBuilder sb = new StringBuilder("abc");
        sb.append("123").insert(3, "-").delete(0, 1);
        System.out.println(sb); // bc-123 (a cut, - added!)
    }
}

3. Method Quick-Map (same as Buffer!)

Method	Example → Result
append(x)	"hi"+1 → hi1
insert(i,x)	"hlo".insert(1,"el") → hello
delete(a,b)	cut a to b-1
reverse()	"abc" → cba
toString()	builder → String (for .equals!)

4. Traps

• sb.reverse() edits in place AND returns same (call twice = back to original!).
• new StringBuilder(s).reverse().toString() — one-liner palindrome (memorize!).
• delete end excluded (like substring!).

5. Exam Points

• Palindrome + chain program — 5-7 marks, very frequent.
• Buffer vs Builder methods identical — 2 marks, frequent.