I am looking to find the best implementation that would basically be a singleton strategy delegate design pattern. What would be the best/cleanest way to create singleton functionals in Java? I want to prevent unnecessary instance creation. I also want to make it so I can look up the correct function without doing a switch or having multiple if statements.I also don’t want to use reflection. Here are a couple different approaches that I found:

public interface Executable extends Serializable{    void execute(); } public class ActionA implements Executable{    ActionA(){    }     void execute(){       //Do Action A     } }  public class ActionB implements Executable{     ActionB(){     }     void execute(){       //Do Action B     } }  public enum Action{     ACTION_A(new ActionA()),     ACTION_B(new ActionB());      private executable;     private Action(Executable e){         executable =e;     }     public Executable getExecutable(){         return e;     } }  public class Service{       public static doService(Action input){          //preAction           action.execute();          //postAction      }   } public class AlternateServiceImplementation(){     //Action no longer would contain the executable instances     private static Map<> actionMap = new EnumMap<Action,Executable>;     static{            actionMap.put(ACTION_A,new ActionA());            actionMap.put(ACTION_B,new ActionB());     }     public static doService(Action action){           //preAction           Executable executable=actionMap.get(action);           executable.execute();           //postAction      } }