Java design pattern-Abstract Factory pattern (Abstract Factory)

Java design pattern-Abstract Factory pattern (Abstract Factory)
Purpose: provide an interface to create a family of mutually dependent objects without explicitly specifying the object class.

When to use: A system should not depend on the details of how product instances are created, combined, and expressed. This is important for all forms of factory models.
This system has more than one product family, and the system only consumes one of them.
Products belonging to the same product family are used together. This constraint must be reflected in the system design.
The system provides a product library. All products use the same interface, so that the client does not rely on implementation.
Actual Example: javax. xml. parsers. DocumentBuilderFactory
Sample Code:

public class App {public static void main(String[] args) {createKingdom(new ElfKingdomFactory());createKingdom(new OrcKingdomFactory());}public static void createKingdom(KingdomFactory factory) {King king = factory.createKing();Castle castle = factory.createCastle();Army army = factory.createArmy();System.out.println(The kingdom was created.);System.out.println(king);System.out.println(castle);System.out.println(army);}}

public interface King {}public interface Castle {}public interface Army {}public interface Army {}

public interface KingdomFactory { Castle createCastle(); King createKing(); Army createArmy(); }

public class ElfKingdomFactory implements KingdomFactory {public Castle createCastle() {return new ElfCastle();}public King createKing() {return new ElfKing();}public Army createArmy() {return new ElfArmy();}}

public class OrcKingdomFactory implements KingdomFactory {public Castle createCastle() {return new OrcCastle();}public King createKing() {return new OrcKing();}public Army createArmy() {return new OrcArmy();}}

public class ElfArmy implements Army {@Overridepublic String toString() {return This is the Elven Army!;}}

public class ElfKing implements King {@Overridepublic String toString() {return This is the Elven king!;}}

public class ElfCastle implements Castle {@Overridepublic String toString() {return This is the Elven castle!;}}

public class OrcArmy implements Army {@Overridepublic String toString() {return This is the Orcish Army!;}}

public class OrcCastle implements Castle {@Overridepublic String toString() {return This is the Orcish castle!;}}

public class OrcKing implements King {@Overridepublic String toString() {return This is the Orc king!;}}

Output result:

The kingdom was created.This is the Elven king!This is the Elven castle!This is the Elven Army!The kingdom was created.This is the Orc king!This is the Orcish castle!This is the Orcish Army!