Intern / FresherJava
What is the difference between String, StringBuilder and StringBuffer in Java?
Quick answer
String is immutable, StringBuilder is a mutable and fast but not thread-safe buffer, and StringBuffer is a mutable buffer with synchronized methods that is thread-safe but slower.
Because String is immutable, every concatenation creates a new object, so building text in a loop with += is wasteful. Immutability also makes strings safe to share between threads, cache their hash code and use as HashMap keys, and it is what allows the string pool.
Use StringBuilder for building text in a single thread, which is almost always. StringBuffer is a legacy class from Java 1.0 and is rarely needed, since sharing a builder across threads is uncommon and you usually need your own higher-level synchronisation anyway.
StringBuilder sb = new StringBuilder();
for (int i = 0; i < 5; i++) {
sb.append(i).append(',');
}
String result = sb.toString(); // "0,1,2,3,4,"