[Design Pattern] Command Pattern Simple Case

Command pattern, which is the pattern of commands, wraps a command in an object, passes the command object to the executor of the command, and belongs to the design pattern of the behavior class.

Here is a simple case of the command pattern.

The Stock represents the object being manipulated. The order defines the interface of the command, BuyStock, Sellstock is the concrete class that implements the order interface. The Broker is the executor of the command. Commandpatterndemo demonstrates the command mode.

Code implementation

Order, Command interface

 Public Interface Order {    publicvoid  execute ();}

The specific command class

 Public class Implements Order {    private  stock stock;          Public BuyStock (stock stock) {        this. Stock= stock;    }        @Override    publicvoid  execute () {        stock.buy ();    }}

 Public class Implements Order {    private  stock stock;          Public Sellstock (stock stock) {        this. Stock= stock;    }        @Override    publicvoid  execute () {        Stock.sell ();    }}

Broker, Performer of command

Importjava.util.LinkedList;Importjava.util.List; Public classBroker {Privatelist<order> orders =NewLinkedlist<>();  Public voidTakeorder (Order order) {Orders.add (order); }         Public voidplaceorders () { for(Order order:orders) {order.execute (); }    }}

Demo Command mode

 Public class Commandpatterndemo {    publicstaticvoid  main () {        new Stock ("Apple", +);                 New BuyStock (stock);         New Sellstock (stock);                         New Broker ();        Broker.takeorder (buystock);        Broker.takeorder (sellstock);                Broker.placeorders ();    }}

Consider extensibility

When you need to add a command operation, such as Freezestock:

1. Add a file to implement the Freezestock class so that it implements the Order interface.

2. Add the Freeze method to the Stock

3. Call the new Freezestock object in the client, class implementation command.

You can achieve the effect of new operations without modifying the code of the command executor Broker.

Resources

Design Patterns-command Pattern, Tutorialspoint

[Design Pattern] Command Pattern Simple Case