Lazy initialization

lazy

Lazy initialization has two objectives:
  1. delay an expensive operation until it's absolutely necessary
  2. store the result of that expensive operation, such that you won't need to repeat it again.
  
To avoid a NullPointerException, a class must self-encapsulate fields that have lazy initialization. 
That is, a class cannot refer directly to such fields, but must access them through a method.

The hashCode method of an immutable Model Object is a common candidate for lazy initialization.

public final class Lazyer {
  
  private int mId;
  private String mName;
  private int hashCode;
  private List<String> mPigs;
  
  public Lazyer() {
    mId = 1;
    mName = "beep";
  }
  
  public List<String> getPigs() {
    if(mPigs == null) {
      List<String> pigs = new ArrayList<>();
      ****
      mPigs = pigs;
    }
    
    return mPigs;
  }
  
  public int hashCode() {
    if(hashCode == 0) {
      ****
      hashCode = HashCodeUtil.hashCode(/**what ever you want**/);
    }
    
    return hashCode;
  }
}

public final class Printers {
  
  private static List<PrintService> services;
  
  void print(String someThing, PrintService printService) {
    
  }
  
  List<PrintService> getAvailablePrintService(PrintAttributeSet attrs) {
    if(services == null) {
      //Do something with attribute set to get the printers
      services = PrintServiceLookup.lookupAvaiableService(attrs);
    }
    
    return services;
  }
}