Does StringBuilder creates a new String in every operation?

Question

How many objects were created with this code? - I know the 3 String literals are in the String Constant Pool and the StringBuilder object is at the heap but does it creates a new String in the pool when i call reverse(), insert() or append() ?

StringBuilder sb = new StringBuilder("abc");
sb.append("def").reverse().insert(3, "---");
System.out.println( sb );

Answer 1

StringBuilder will only create a new string when toString() is called on it. Until then, it keeps an char[] array of all the elements added to it.

Any operation you perform, like insert or reverse is performed on that array.

Answer 2

Strings created: "abc", "def", "---"

StringBuilders created: sb

sb.append("def").reverse().insert(3, "---") are not creating new objects, just editing the StringBuilder's internal buffer (that's why using StringBuilder is recomended for performances).