Implementing the Decorator pattern

Let's look at the following code to demonstrate the Decorator design pattern.

Create a component class:

Following is the Account.java file:

    package com.packt.patterninspring.chapter3.decorator.pattern; 
    public interface Account { 
       String getTotalBenefits(); 
    } 

Create concrete components classes:

Following is the SavingAccount.java file:

    package com.packt.patterninspring.chapter3.decorator.pattern; 
    public class SavingAccount implements Account { 
      @Override 
      public String getTotalBenefits() { 
         return "This account has 4% interest rate with per day
           $5000 withdrawal limit"; 
      } 
    } 

Let's create another concrete class for Account component:

Following is the CurrentAccount.java file:

    package com.packt.patterninspring.chapter3.decorator.pattern; 
    public class CurrentAccount implements Account { 
      @Override 
      public String getTotalBenefits() { 
         return "There is no withdrawal limit for current account"; 
      } 
    } 

Let's create a Decorator class for Account component. This decorator class apply other run time behavior to the Account component classes.

Following is the AccountDecorator.java file:

    package com.packt.patterninspring.chapter3.decorator.pattern; 
    public abstract class AccountDecorator implements Account { 
      abstract String applyOtherBenefits(); 
    } 

Let's create a ConcreteDecorator class to implement the AccountDecorator class. Following class SeniorCitizen is extended AccountDecorator class to access other run time behavior such as applyOtherBenefits().

Following is the SeniorCitizen.java file:

    package com.packt.patterninspring.chapter3.decorator.pattern; 
    public class SeniorCitizen extends AccountDecorator { 
      Account account; 
      public SeniorCitizen(Account account) { 
         super(); 
         this.account = account; 
      } 
      public String getTotalBenefits() { 
         return account.getTotalBenefits() + " other benefits are 
             "+applyOtherBenefits(); 
      } 
      String applyOtherBenefits() { 
         return " an medical insurance of up to $1,000 for Senior 
         Citizen"; 
      } 
    } 

Let's create another ConcreteDecorator class to implement the AccountDecorator class. Following class Privilege is extended AccountDecorator class to access other run time behavior such as applyOtherBenefits().

Following is the Privilege.java file:

    package com.packt.patterninspring.chapter3.decorator.pattern; 
    public class Privilege extends AccountDecorator { 
      Account account; 
      public Privilege(Account account) { 
         this.account = account; 
      } 
      public String getTotalBenefits() { 
         return account.getTotalBenefits() + " other benefits are    
            "+applyOtherBenefits(); 
      } 
      String applyOtherBenefits() { 
        return " an accident insurance of up to $1,600 and
           an overdraft facility of $84"; 
        } 
      } 

Let's now write some test code to see how the Decorator pattern works at runtime:

Following is the DecoratorPatternMain.java file:

    package com.packt.patterninspring.chapter3.decorator.pattern; 
    public class DecoratorPatternMain { 
      public static void main(String[] args) { 
         /*Saving account with no decoration*/ 
         Account basicSavingAccount = new SavingAccount(); 
         System.out.println(basicSavingAccount.getTotalBenefits()); 
         /*Saving account with senior citizen benefits decoration*/ 
         Account seniorCitizenSavingAccount = new SavingAccount(); 
         seniorCitizenSavingAccount = new 
            SeniorCitizen(seniorCitizenSavingAccount); 
         System.out.println
        (seniorCitizenSavingAccount.getTotalBenefits()); 
         /*Saving account with privilege decoration*/ 
         Account privilegeCitizenSavingAccount = new SavingAccount(); 
         privilegeCitizenSavingAccount = new
            Privilege(privilegeCitizenSavingAccount); 
         System.out.println
        (privilegeCitizenSavingAccount.getTotalBenefits()); 
      } 
    } 

Let's run this demo class and see the following output at the console: