Lazy Initialization

The tactic of delaying object creation or module initialization(modules pattern) up until it is required.

We have
Initializable interface: which is where initialization happen,

public interface Initializable {
    public void init();
    public boolean initialized();
    public boolean isLazyInit();
    public void setInited(boolean status);
    public String getName();
} 

InitializationDirector : which does the initialization of required object,

public class InitializationManager {

 public static void  initialize(String module){
  for(Initializable registered:InitializableRegistry.getInits()){
   if(registered.name().equalsIgnoreCase(module))
    initialize(registered);
  }
 }
 public static void initAll(){
  for(Initializable registered:InitializableRegistry.getInits()){
   initialize(registered);
  }
 }
 public static void initialize(Initializable initializable){
  if(!initializable.initialized()){
   initializable.init();
   initializable.setInited(true);
  }
 }
}

InitializableRegistry  : registry of all initializables

public class InitializableRegistry {

 private static List<Initializable> initializables=new ArrayList<Initializable>(5);
 public static void registerInitializable(Initializable init){
  if(!init.isLazyInit()){
   System.out.println("initializing "+init.name()+" on registeration");
   init.init();
   init.setInited(true);
  }
  initializables.add(init);
 }
 public static List<Initializable> getInits(){
  return initializables;
 }
} 

Test,

public class LazyInitDemo {

 public static void main(String[] args) {
  InitializableRegistry.registerInitializable(new EngineCheck());
  InitializableRegistry.registerInitializable(new EmergencySetups());
  InitializableRegistry.registerInitializable(new AutoPilot());
  InitializableRegistry.registerInitializable(new FlightPath());
  
  System.out.println("---lazy init on demand of particular module");
  InitializationManager.initialize("FlightPath");
  
  System.out.println("---init whatever is left");
  InitializationManager.initAll();
 }
} 

sample output

initializing EngineCheck on registeration
initing Engine check
initializing Emergency on registeration
initing emergency modules
---lazy init on demand of particular module
initing FlightPath module
---init whatever is left
initing AutoPiloting