StringBuffer Class Methods

StringBuffer Class Methods

1. Core Idea (beginner)

All methods edit SAME object (return this for chaining!). No new garbage like String. Master 6: append, insert, delete, reverse, replace, capacity/length.

2. Code — One Object, Many Edits (watch it morph!)

StringBuffer sb = new StringBuffer("hello");
sb.append("!");              // hello! (add end)
sb.insert(5, " world");      // hello world! (insert at 5!)
sb.delete(5, 11);            // hello! (delete 5 to 10!)
sb.replace(0, 5, "bye");     // bye! (replace 0-4!)
sb.reverse();                // !eyb (flip!)
System.out.println(sb);      // !eyb
System.out.println(sb.length() + "/" + sb.capacity()); // 4/21
sb.setLength(0);             // clear! (empty, capacity kept!)

Chaining (returns same!): sb.append("a").append("b").reverse();

3. Method Table (exam!)

Method	Job	Example → Result
append(x)	add end	"hi".append("!") → hi!
insert(i,x)	insert at i	"hlo".insert(1,"el") → hello
delete(a,b)	cut a to b-1	"hello".delete(1,4) → ho
reverse()	flip	"abc".reverse() → cba
replace(a,b,s)	swap range	"hello".replace(1,4,"ipp") → hippo
setCharAt(i,c)	single change	"hit".setCharAt(1,'e') → het

4. Traps

• delete(5,11) end EXCLUDED (like substring!).
• toString() to get String: String s = sb.toString(); (needed for .equals content compare!).
• capacity() ≠ length() (room vs used!).

5. Exam Points

• 6 methods with output — 7 marks, very frequent.
• Chaining + delete-range trap — 3-5 marks, frequent.