Java 1.5 introduced a new interface, java.io.Closeable, that contains a
single method:
void close();
This interface factors out the behavior of having a method that disposes
of a particular instance, making any system resources associated with it
available for reuse. Classes in java.io that have a close() method were
retrofitted to implement this interface.

Classes in java.net, in particular, the various socket classes, also provide
a close() method matching this signature and behavior. However, they were
not retrofitted to implement the Closeable interface. They should be.