Callable和Future

一直想讓子線程跑起來後將結果傳遞給主線程，在對Runable失望後，最終找到了Callable和Future這兩個接口，完美知足了個人需求。 最大的區別就是Runable返回void，而Callable返回V或者異常。

JDK中描述以下：

A task returns a result and may throw an exception. Implementors define a single method with no arguments called call.

The Callable interface is simillar to Runnable, in that both are designed for classes whose instances are potentially executed by another thread. A Runnable, however, does not return a result and cannot throw a checked exception.

The Executors class contains utility methods to convert from other common forms to Callable classes.