The Factory Method pattern

Problem: A class needs to instantiate a derivation of another class, but doesn't know which one.
Solution: The Factory Method defines an interface for creating objects, but lets subclasses decide which classes to instantiate.

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public interface Logger {     void debug(String message); // implicitly public }

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public class FileLogger implements Logger {     @Override public void debug(String message) { ... } }

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public abstract class AbstractLoggerFactory {     public abstract Logger createLogger(); // factory method       public Logger getLogger() {         Logger logger = createLogger();         ...         return logger;     } }

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public class FileLoggerFactory extends AbstractLoggerFactory {     @Override     public Logger createLogger() {         return new FileLogger();     } }

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public class Client {     private AbstractLoggerFactory factory = new FileLoggerFactory();     public doSomething(AbstractLoggerFactory factory) {         Logger logger = factory.getLogger();         logger.debug("debug message");     } }