String is immutable: you can’t modify a string object but can replace it by creating a new instance. Creating a new instance is rather expensive.
StringBuffer is mutable: use StringBuffer or StringBuilder when you want to modify the contents. StringBuilder was added in Java 5 and it is identical in all respects to StringBuffer except that it is not synchronised, which make it slightly faster at the cost of not being thread-safe.
StringBuffer expands as needed, which is costly however, so it would be better to initilise the StringBuffer with the correct size from the start as shown.
Another important point is that creation of extra strings is not limited to ‘overloaded mathematical operators’ (“+”) but there are several methods like concat(), trim(), substring(), and replace() in String classes that generate new string instances. So use StringBuffer or StringBuilder for computation intensive operations, which offer better performance.
StringBuffer is mutable: use StringBuffer or StringBuilder when you want to modify the contents. StringBuilder was added in Java 5 and it is identical in all respects to StringBuffer except that it is not synchronised, which make it slightly faster at the cost of not being thread-safe.
StringBuffer expands as needed, which is costly however, so it would be better to initilise the StringBuffer with the correct size from the start as shown.
Another important point is that creation of extra strings is not limited to ‘overloaded mathematical operators’ (“+”) but there are several methods like concat(), trim(), substring(), and replace() in String classes that generate new string instances. So use StringBuffer or StringBuilder for computation intensive operations, which offer better performance.
