Design Patterns | Command

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1. References
2. Example
   • The Receiver
   • The Concrete Receiver (1)
   • The Concrete Receiver (2)
   • The Command
   • The Concrete Command
   • The Caller
   • A simple class to test the Command design pattern

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1. References
   • Definition: (source: http://en.wikipedia.org/wiki/Command_pattern)
     
     The Command pattern is a behavioral design pattern in which an object is used to encapsulate all information needed to perform an action or trigger an event at a later time.
     
     
   • Class diagram: (source: http://en.wikipedia.org/wiki/Command_pattern)
     
     
2. Example
   • The Receiver:
     
     public interface Payment { void apply(); }
     
   • The Concrete Receiver (1):
     
     public class Debit implements Payment { public void apply() { System.out.println("debit ..."); } }
     
   • The Concrete Receiver (2):
     
     public class Credit implements Payment { public void apply() { System.out.println("credit ..."); } }
     
   • The Command:
     
     public interface Transaction { void apply(); }
     
   • The Concrete Command:
     
     public class TransactionImpl implements Transaction { private Payment payment; public TransactionImpl(final Payment payment) { this.payment = payment; } public void apply() { payment.apply(); } }
     
   • The Caller:
     
     public class Operator { private Transaction transaction; public void setTransaction(final Transaction transaction) { this.transaction = transaction; } public void apply() { transaction.apply(); } }
     
   • A simple class to test the Command design pattern:
     
     public class CommandPatternTest { public static void main(String[] args) { // create the payment Payment payment = new Debit(); // create the transaction Transaction transaction = new TransactionImpl(payment); // create the operator Operator operator = new Operator(); operator.setTransaction(transaction); // call methods operator.apply(); } }