If we follow traditional approach to create a thread or implement a runnable interface, then we have certain limitations.

Time Consuming - every time we need to create a thread its time and resource consuming.
Poor Resource Management - Lets take a example of our application creates 1000 threads and only 500 threads is used remaining thread lies as not used.
Robust - if a million threads access came our application stops.

To overcome this Executer framework was introduced to overcome this. It overcomes the limitations of thread.

It will have a pool of thread whenever needed a thread perform a task and again moved to pool.

Callable and future - using runnable we cannot return a value. To overcome this callable is introduced. Call method is