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More Occam's Razor C to Java Translator Theory of Morality II


A Super Constructor design pattern Free Stuff

Abstract

This article presents a Super Constructor design pattern. It is equally suitable for C++ and Java.

The design pattern

This design pattern is applicable in cases where the constructor could return a null value or where you want to have a virtual constructor. To do this, the constructor needs to be renamed to a static method called for arguments sake: ctor. Here is the design pattern for null return values in action in the Java language:


class Foo
{
   int aProperty;

   private Foo(/* parameters */)
   {
      /* your code goes here */
   }

   public static Foo ctor(/* parameters */)
   {
      Foo returnValue = new Foo(/* arguments */);
      /* set properties here */
      returnValue.aProperty = 123;
      /* decide whether or not to return null here */
      if (/* code omitted */)
      {
         return returnValue;
      }
      else
      {
         return null;
      }
   }
}

The name ctor is used to remind the client that the method serves in the role of a constructor. The actual constructor is private so that it can only invoked indirectly by the ctor function. Here is the design pattern in action when you want to have a virtual constructor:


class Root
{
   private Root(/* parameters */)
   {
      /* your code goes here */
   }

   public static Root ctor(/* parameters */)
   {
      if (/* code omitted */)
      {
         return new Root(/* arguments */);
      }
      else if (/* code omitted */)
      {
         return new SubClass(/* arguments */);
      }
      else
      {
         return null;
      }
   }

   /* your code goes here */
}

class SubClass extends Root
{
   public SubClass(/* parameters */)
   {
      /* your code goes here */
   }

   /* your code goes here */
}

Here is an alternative implementation of the Super Constructor design pattern:


class Root
{
   public Root(/* parameters */)
   {
      /* your code goes here */
   }
}

class SubClass extends Root
{
   public static Root ctor(/* parameters */)
   {
      if (/* code omitted */)
      {
         return new Root(/* arguments */);
      }
      else if (/* code omitted */)
      {
         return new SubClass(/* arguments */);
      }
      else
      {
         return null;
      }
   }
}


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| Main Menu | Research Projects | Photo Album | Curriculum Vitae | The Greatest Artists |
| Email Address | Computer Games | Web Design | Java Training Wheels | The Fly (A Story) |
| Political Activism | Bob Dylan Quotes+ | My Life Story | Smoking Cessation | Other Links |
| Debugging Macros | String Class I | Linked List System I | Java for C Programmers | Naming Convention |
| String Class II | How I use m4 | Strings III | Symmetrical I/O | Linked Lists II |
| Run-Time Type Info | Virtual Methods | An Array System | Science & Religion | Submodes |
| Nested Packages | Memory Leaks | Garbage Collection | Internet & Poverty | What is Knowledge? |
| Limits of Evolution | Emacs Additions | Function Plotter | Romantic Love | The Next Big Thing |
| Science Fiction | Faster Compilation | Theory of Morality | Elisp Scoping | Elisp Advice |
| S.O.G.M. Pattern | Safe Properties | School Bullying | Charisma Control | Life and Death |
| Splitting Java | Multiple Ctors | Religious Beliefs | Conversation 1 | Conversation 2 |
| J.T.W. Language | Emacs Additions II | Build Counter | Relation Plotter | Lisp++ Language |
| Memory Leaks II | Super Constructors | CRUD Implementation | Order a Website Form | There Is An Afterlife |
| More Occam's Razor | C to Java Translator | Theory of Morality II
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