Java: How command pattern is used in popular libraries

Real-World Library Implementations

Many well-known Java libraries and frameworks use the Command Pattern internally to facilitate the construction of complex objects. Below are five commonly cited examples in the standard Java libraries that illustrate the Command Pattern (encapsulating an action — or “command” — as an object).

1) Executor.execute(Runnable command) (Concurrency Framework)

Where it appears

• Package: java.util.concurrent
• Key Interfaces/Classes: Executor, Runnable

How it demonstrates the Command pattern

• The Runnable interface represents a command—its single run() method captures the action to be performed.
• By passing a Runnable to an Executor (e.g., a ThreadPoolExecutor), you are scheduling or queuing the execution of that command.
• The execute(Runnable command) method tells the executor to “run this command object at some point.”

Executor executor = Executors.newSingleThreadExecutor();
Runnable command = () -> System.out.println("Hello from a command!");
executor.execute(command);  // Schedules the command's execution