Static Factory Method Example (using Java)

ExampleToUseToyFactory.java

import java.util.ArrayList;
import java.util.List;
import java.util.Objects;

public class ExampleToUseToyFactory {

  public static void main( String[] args ) {
    // PREVENTED TO USE `new` KEYWORD
    // Toy toy = new Toy( "???" );

    // Use STATIC FACTORY METHOD
    Toy woody = Toy.Factory( "Woody_Pride", 34000, "main-product" );
    Toy buzz = Toy.Factory( "Buzz_Lightyear", 28000, "main-product" );
    Toy potato = Toy.Factory( "Mr._Potato", -999999 );

    List<Toy> toyTray = new ArrayList<>();
    toyTray.add( woody );
    toyTray.add( buzz );
    toyTray.add( potato );
    
    String myFavoriteToyName = "Woody_Pride";
    selectMyFavoriteToy( toyTray, myFavoriteToyName );
  }

  private static void selectMyFavoriteToy( List< Toy> toyTray, String myFavoriteToyName ) {
    if ( Objects.isNull( myFavoriteToyName ) || myFavoriteToyName.isBlank() ) {
      System.out.println( "Oops! Missing myFavoriteToyName..." );
      return;
    }

    for ( Toy toyFromTray : toyTray ) {
      toyFromTray.printToyInfo();
      if ( myFavoriteToyName.equals( toyFromTray.toyName ) ) {
        System.out.println( "I Love " + myFavoriteToyName + "!! :D" );
        return;
      }
    }

    System.out.println( "My Favorite Toy is not in this tray..." );
  }

}

Toy.java

import java.util.Objects;

public class Toy {

  /*
   * --------------------------
   * IMMUTABLE MEMBER VARIABLES
   * --------------------------
   */
  public final String toyName;
  public final int    toyPrice;
  public final String toyDesc;

  /*
   * --------------------------------
   * STATIC FACTORY METHOD
   * > ALLOW TO ALLOCATE NEW INSTANCE
   * --------------------------------
   */
  public static Toy Factory( String toyName, int toyPrice, String toyDesc ) {
    toyName  = checkBeforeAllocateToyName(toyName);
    toyPrice = checkBeforeAllocateToyPrice(toyPrice);
    final Toy toy = isInvalidString( toyDesc )
                      ? new Toy( toyName, toyPrice )
                      : new Toy( toyName, toyPrice, toyDesc );
    return postStep(toy);
  }

  /*
   * --------------------------------------------------------------------
   * PRIVATE OVERLOADED CONSTRUCTORS
   * > DENY TO ALLOCATE NEW INSTANCE WITH `new` KEYWORD FROM OUT OF CLASS
   * --------------------------------------------------------------------
   */
  private Toy( String toyName, int toyPrice ) {
    this.toyName  = toyName;
    this.toyPrice = toyPrice;
    this.toyDesc  = "(none)";
  }

  private Toy( String toyName, int toyPrice, String toyDesc ) {
    this.toyName  = toyName;
    this.toyPrice = toyPrice;
    this.toyDesc  = toyDesc;
  }

  /*
   * ----------------------------------------------------
   * PRIVATE METHOD FOR VALIDATION BEFORE ALLOCATE VALUES
   * ----------------------------------------------------
   */
  private String checkBeforeAllocateToyName( String toyName ) {
    if ( isInvalidString( toyName ) ) {
      System.out.println( "> WARN | Toy-Check | Invalid ToyName: " + toyName + " > set default: " + getDefaultToyName() );
      return getDefaultToyName();
    }
    System.out.println( ">DEBUG | Toy-Check | ToyName: " + toyName );
    return toyName;
  }

  private boolean isInvalidString( String str ) {
    return Objects.isNull( str ) || toyName.isBlank();
  }
  
  private String getDefaultToyName() {
    return "NO_NAMED";
  }

  private int checkBeforeAllocateToyPrice(int toyPrice) {
    boolean isNeedToSetDefault = toyPrice <= 0;
    if (isNeedToSetDefault) {
      System.out.println( "> WARN | Toy-Check | Invalid ToyPrice: " + toyPrice + " > set default: " + getDefaultToyPrice() );
      return getDefaultToyPrice();
    }
    System.out.println( ">DEBUG | Toy-Check | ToyPrice: " + toyPrice );
    return toyPrice;
  }

  private int getDefaultToyPrice() {
    return 25000;
  }
  
  private Toy postStep(Toy newToy) {
    // Something to common post-step (after calling constructor)
    newToy.printToyInfo();
    return newToy;
  }
  
  /*
   * ------------------------------------
   * PUBLIC METHOD FOR ALLOCATED INSTANCE
   * ------------------------------------
   */
  public void printToyInfo() {
    System.out.println( toString() );
  }

  @Override
  public String toString() {
    StringBuilder toyInfo = new StringBuilder();
    toyInfo.append( "> " + toyName );
    toyInfo.append( " (" + toyPrice + " KRW)" );
    return toyInfo.toString();
  }
  
}

Factory Method

• Use
• Define
  • condition for constructor
  • private constructors: Prevented to use new keyword.
  • common post-step in Factory Method
  • private methods
  • other public methods