In JDK 8, StringBuffer class has a toStringCache , while StringBuilder doesn't. /** * A cache of the last value returned by toString. Cleared * whenever the StringBuffer is modified. */ private transient char[] toStringCache; But why? One possible reason I can think of is that StringBuffer is already synchronized so a cache can be implemented easier. Or maybe historically StringBuffer was implemented this way so old code depends heavily on this feature? Given modern JVM with escape analysis and biased locking, is the difference relevant anymore?

Why StringBuffer has a toStringCache while StringBuilder not?

In JDK 8, StringBuffer class has a toStringCache, while StringBuilder doesn't.

/**
 * A cache of the last value returned by toString. Cleared
 * whenever the StringBuffer is modified.
 */
private transient char[] toStringCache;

But why?

One possible reason I can think of is that StringBuffer is already synchronized so a cache can be implemented easier.
Or maybe historically StringBuffer was implemented this way so old code depends heavily on this feature?

Given modern JVM with escape analysis and biased locking, is the difference relevant anymore?