Command pattern java API usage

Question

I'm trying to memorize design patterns as best as I can.

I understood the best way is to see where design patterns being used in the Java API.

Can someone provide me other Java API examples of the command pattern other than classics like Java Swing and the Runnable interface?

Answer 1

Description on wiki is here

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Important Points on Command Pattern

• Command pattern helps to decouple the invoker and the receiver. Receiver is the one which knows how to perform an action.
• Command helps to implement call back in java. Helps in terms of extensibility as we can add new command without changing existing code.
• Command defines the binding between receiver and action.
• A command should be able to implement undo and redo operations. That is restting the state of the receiver. It can be done from the support of receiver.

Command Pattern in Java API

Implementations of java.lang.Runnable and javax.swing.Action follows command design pattern , and as @Dave Newton said They're pretty good examples.Then you don't need to find out another much better examples in the java api .

Example

I have an example about using runnable with swing. In the code below Runnable object (command) is send to a method as argument and can be invoked at any time.

Runnable runnable = new Runnable() {
    @Override
    public void run() {
        this.label.setText("Updated text");
    }
};
SwingUtilities.invokeLater(runnable);

Summary

The command pattern is a powerful and flexible design idiom, commonly used in Graphical User Interface design to handle events and commands issued by a user. Design patterns are intended to allow greater modularity when designing programs, reducing the dependencies placed on any given block of code.

Practise Exercise

Using the command pattern , Create a small app which simulates a simple calculator, with operations such as add, subtract and multiply.