What design pattern is used when implementing the StringBuilder class for efficient string operations?

The StringBuilder class is implemented using the "Builder" design pattern. This pattern allows for the efficient creation of complex objects (in this case, strings) step by step, avoiding the creation of many intermediate objects.

In the context of StringBuilder, this means that strings are accumulated in a mutable buffer, which is much more efficient than concatenating immutable strings.

Example of using StringBuilder in Java:

StringBuilder sb = new StringBuilder();
sb.append("Hello");
sb.append(" ");
sb.append("World");
String result = sb.toString(); // "Hello World"

Thus, the "Builder" pattern helps manage the process of constructing a string and optimizes memory usage.