docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/StringBuffer.html StringBuffer (Java SE 15 & JDK 15) All Implemented Interfaces: Serializable, Appendable, CharSequence, Comparable public final class StringBuffer extends Object implements Serializable, Comparable , CharSequence A thread-safe, mutable sequence of characters. A string buffer is like a String docs.oracle.com java.lang..