A task that returns a result and may throw an exception. Implementors define a single method with no arguments called call.
The Java Callable interface is similar to the Java Runnable interface, in that both of them represents a task that is intended to be executed concurrently by a separate thread. A Java Callable is different from a Runnable in that the Runnable interface's run() method does not return a value, and it cannot throw checked exceptions (only RuntimeExceptions). Additionally, a Runnable was originally designed for long running concurrent execution, e.g. running a network server concurrently, or watching a directory for new files. The Callable interface is more designed for one-off tasks that return a single result.
The Executors class contains utility methods to convert from other common forms to Callable classes.