Cheatsheet of Standard Design Patterns implemented using Java 8 Lambdas

Java 8 Patterns Cheatsheet.md

Design Patterns implemented in Java 8

These patterns are implemented using Java 8 Lambdas (together with Project Lombok annotations).

Factory Pattern

Factory I : No Parameter Constructor

Enum class:

@RequiredArgsConstructor
@Getter
public static enum ShapeType {
   CIRCLE( Circle::new),
   RECTANGLE( Rectangle::new);

   private final Supplier<Shape> constructor;
}

Factory method:

public static Shape createShape( ShapeType type) {
   return type.getConstructor().get();
}

Factory II : Parameterised Constructor

Enum class:

@RequiredArgsConstructor
@Getter
public static enum ShapeType {
   CIRCLE( s, t -> new Circle( s, t)),
   RECTANGLE( s, t -> new Rectangle( s, t));

   private final ShapeConstructor constructor;
}

Functional Interface:

@FunctionalInterface
public interface ShapeConstructor {
   Shape create( String s, int t);
}

Factory method:

public static Shape createShape( ShapeType type, String name, int line) {
   return type.getConstructor().create( name, line);
}

Factory III : Factory Function

Enum class:

@RequiredArgsConstructor
@Getter
public enum ShapeType {
   CIRCLE( s, t -> new Circle( s, t)),
   RECTANGLE( s, t -> new Rectangle( s, t));

   private final ShapeConstructor constructor;
}

Functional Interface:

@FunctionalInterface
public interface ShapeFactory {
   Shape create( String s, int t);
}

Factory method:

public static ShapeFactory createFactory( ShapeType type) {
   return type.getConstructor();
}

Factory use (version 1 - static factory replacement):

ShapeFactory.createFactory( CIRCLE).create( Color.RED, 2)

Factory use (version 2 - factory instance replacement):

ShapeFactory factory = ShapeFactory.createFactory( RECTANGLE);
...
Shape newShape = shapeFactory.create( Color.YELLOW, 1);

Strategy Pattern

Strategy Interface:

public interface TextFormatStrategy {
   Predicate<String> getFilter();
   UnaryOperator<String> getFormatter();
}

Enum class:

@RequiredArgsConstructor
@Getter
public static enum StrategyType implements TextFormatStrategy {
   PLAIN_TEXT( t -> true,
               t -> t),
   ERROR_TEXT( t -> t.startsWith( "ERROR" ),
               t -> t.toUpperCase()),
   SHORT_TEXT( t -> t.length() < 20 ,
               t -> t.toLowerCase());

   private final Predicate<String> filter;
   private final UnaryOperator<String> formatter;
}

Usage Pattern Version I

Usage - passing all the data into the recipient method:

public static void publishText(String text, TextFormatStrategy formatStrategy) {
   if ( formatStrategy.getFilter().test( text )) {
      System.out.println( formatStrategy.getFormatter().apply( text ) );
   }
}
...
List<String> messages = Arrays.asList( "DEBUG - I'm here", "ERROR - something bad happened");
messages.forEach( t -> publishText( t, TextFormatStrategy.StrategyType.PLAIN_TEXT));

Usage Pattern Version II

Usage - passing just the strategy and returning a functional method to receive the parameters:

public static Consumer<String> publishText( TextFormatStrategy formatStrategy) {
   return t -> {
      if ( formatStrategy.getFilter().test( t )) {
         System.out.println( formatStrategy.getFormatter().apply( t) );
   }};
}
...
List<String> messages = Arrays.asList( "DEBUG - I'm here", "ERROR - something bad happened");
messages.forEach( publishText( TextFormatStrategy.StrategyType.PLAIN_TEXT)::accept);