Java class definition: Programmer Checklist

A great book on improving the quality of your Java is Effective Java by Joshua Bloch.

Below, a few suggestions are given, primarily concerned with the definition a single class (i.e., the suggestions are not about object-oriented design). This check list is not exhaustive.

1. Minimize accessibility (Java tutorial on accessibility of class members)
   • Class acessibility:
     • If class B is used only by class A, make B an inner class of A.
     • If it is a top-level class: Prefer package-private to public.
   • Attribute accessibility: Declare all attributes private.
   • Method accessibiltiy:
     1. Prefer private to package-private.
     2. Prefer package-private to protected.
     3. Prefer protected to public.
   • Local variable accessibility: Minimize the scope of local variables.
2. Minimize mutability
   • If possible, make the class immutable.
   • If it cannot be immutable, minimize the set of attributes that can be modified after it is constructed. Declare final those attributes that are set only when the object is constructed.
   • If it is not extended, declare the class final.
   • If the class is extended, for each method, if it is not overriden in a subclass, declare it final.
   • Declare non-primitive method parameters final. Prefer

     ImageModel getMinImageModel( final List<ImageModel> imageModelList ) { ... }

     to

     ImageModel getMinImageModel( List<ImageModel> imageModelList ) { ... }

3. Maximize readability
   • All team members should agree on, and adhere to, a set of coding conventions.
   • Use semantically meaningful names. Typically:
     • A class name is a noun phrase.
     • An attribute name is a noun phrase, although its values may be adjectives (e.g., red).
     • A method name has a structure <verb><noun phrase> (e.g., getSaveMenuItem).
   • Declare the type of a local variable where it is first used.
4. Reusability
   • Declare the interface, construct the class. For example, prefer

     List<ImageModel> focusImageModel = new LinkedList<ImageModel>();

     to

     LinkedList<ImageModel> focusImageModel = new LinkedList<ImageModel>();

5. Always override the toString method. Your implementation should, for each attribute (with perhaps a few exceptions), invoke its toString. For example,

   /** Provides a String representation of the Task.
    * @return a String representation of the Task:
    *
    */    
   public String toString ()
   {
       StringBuffer taskString = new StringBuffer();
       taskString.append( getClass().getName() ).append(" ");
       taskString.append( taskId.toString() );
       taskString.append( ": $unsetArgs: " ).append($unsetArgs).append(" ");
       if ( inputs == null ) 
       {
           taskString.append( "NONE ").append( getClass() ).append( " " );
       }
       else 
       {
           for ( int i = 0; i < inputs.length; i++ ) 
           {
               taskString.append( i ).append( ": " );
               if (inputs[i] == null ) 
               {
                   taskString.append( "null " );
               }
               else 
               {
                   taskString.append( inputs[i].toString() );
               }
           }
       }        
       return new String ( taskString );
   }