Write a custom event handler in groovy/java

One may write a couple of classes and an interface to achieve event handling without having to implement the Observable/Observer interface. Assume, we have a computer that runs several processes. If it receives a shutdown command, we fire an event to let the running process handle its own clean up method to release resources and halt execution.

interface ShutdownListener{
    public void handle();
}

public class Computer{

    private def listeners = []

    def addShutdownListener(ShutdownListener l){
listeners.add(l)
    }

    def shutdown(){
for(ShutdownListener l : listeners)
l.handle()
    }

    def compute(){ // whatever  }

}

public class Process implements ShutdownListener{

    public void handle(){
// release resources of "this" Process 
// halt execution of self
println("Process ended.");
    }
}

//groovy script start 
def computer = new Computer()
def process = new Process()
computer.addShutdownListener(process)
computer.compute()
computer.shutdown()

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