StringBuilder

StringBuilder is a mutable sequence of characters designed for efficiently constructing and modifying strings. By allowing successive modifications without creating new string objects at each step, it improves performance in scenarios that involve repeated concatenation, formatting, or large text assembly.

In Java, StringBuilder is a class in the java.lang package. It provides methods such as append, insert, delete, reverse, and setLength, along with capacity management and toString for producing the final string. It is not synchronized, which makes it faster in single-threaded contexts compared to StringBuffer, which offers thread safety at the cost of overhead. When thread safety is required, external synchronization or using StringBuffer may be appropriate.

In the .NET framework, a similar concept exists as System.Text.StringBuilder. It supports a broad range of operations, including Append, Insert, Remove, Replace, Clear, and properties like Length and Capacity. Like its Java counterpart, it is not inherently thread-safe, so concurrent access should be coordinated by the caller if used from multiple threads.

General characteristics include a resizable internal character array, amortized constant time for append operations, and automatic growth when more space is needed. This design reduces the overhead associated with string concatenation of many parts, especially in loops or complex construction tasks. However, excessive use or long-lived temporary builders can still impact memory usage, so it is often best suited for assembling large results before finalizing them into an immutable string.

See also: String (immutable), StringBuffer (Java), and language-specific implementations of mutable string builders.