PECS Code.txt

/*
 * adapted from example @ http://stackoverflow.com/questions/2723397/what-is-pecs-producer-extends-consumer-super/2723538#2723538
 * Get And Put Principle (From Java Generics and Collections)
 * 
 * It states,
 * use an extends wildcard when you only get values out of a structure
 * use a super wildcard when you only put values into a structure
 * **** and don’t use a wildcard when you both get and put. ***
 * 
 */

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

public class TestContraVariance {

  List list = new ArrayList<>();

  /*
   * Example for an upper bound wildcard We can not safely add, because we may
   * have `List<Circle>`, `List<Square>`and List<Rectangle>.
   * 
   */
  public void testCoVariance(List<? extends Shape> list) {

    // list.add(new Shape()); // does not compile
    // list.add(new Circle()); // does not compile
    // list.add(new Square()); // does not compile
    // list.add(new Rectangle()); // does not compile
    Shape shape = list.get(0);// compiles
    list.stream().forEach(o -> o.draw()); // does not compile

  }

  /*
   * Example for a lower bound wildcard We can not safely get, because we may
   * have `List<Circle>`, `List<Square>`and List<Rectangle>.
   */
  public void testContraVariance() {

    list.add(new Shape());// compiles
    list.add(new Circle());// compiles
    list.add(new Square());// compiles
    list.add(new Rectangle());// compiles

    // Shape shape = list.get(0); // does not compile
    // list.stream().forEach(o -> o.draw() ); // does not compile
  }

  public static void main(String[] args) {
    TestContraVariance o = new TestContraVariance();

    o.testContraVariance();
    o.testCoVariance(o.list);

    o = null;
  }
}

import org.apache.commons.lang3.builder.ToStringBuilder;

public class Square extends Shape {

  private static String description = "square\n"
      + "skwer/\n"
      + "noun\n"
      + "1a. plane figure with four equal straight sides and four right angles.\n"
      + "2. the product of a number multiplied by itself.\n"
      + "\"a circle's area is proportional to the square of its radius\"\n"
      +"adjective\n"
      + "1. having the shape or approximate shape of a square.\n"
      + "\"a square table\n"
      +"synonyms: quadrilateral, rectangular, oblong, right-angled, at right angles, perpendicular; More\n"
      + "2. denoting a unit of measurement equal to the area of a square whose side is of the unit specified.\n"
      + "\"30,000 square feet of new gallery space\"\n"
      +"adverb\n"
      + "1. directly; straight.\n"
      + "\"it hit me square in the forehead\"\n"
      + "verb\n"
      + "1. make square or rectangular; give a square or rectangular cross section to.\n"
      + "\"you can square off the other edge\"\n"
      + "2. multiply (a number) by itself.\n"
      + "\"5 squared equals 25\n";

  public void draw() {

    System.out.printf("%s\n%s", this.getClass().getName(), description);

  }
}
import org.apache.commons.lang3.builder.ToStringBuilder;
import org.apache.commons.lang3.builder.ToStringStyle;

public class Shape {

  private static String description = "shape\n"
      + "SHāp/Submit\n"
      + "noun\n"
      + "1. the external form or appearance characteristic of someone or something; the outline of an area or figure.\n"
      + "\"she liked the shape of his nose\"\n"
      + "synonyms: form, appearance, configuration, formation, structure; More\n"
      + "2. the particular condition or state of someone or something.\n"
      + "\"he was in no shape to drive\"\n"
      + "synonyms: condition, health, fettle, order\n"
      + "\"you're in pretty good shape\"\n"
      + "verb\n"
      + "1. give a particular shape or form to.\n"
      + "\"most caves are shaped by the flow of water through limestone\"\n"
      + "synonyms: form, fashion, make, mold, model, cast; More\n";


  public void draw() {

    System.out.printf("%s\n%s", this.getClass().getName(), description );
  
  }

@Override
public String toString() {
  return ToStringBuilder.reflectionToString(this);
}

}
public class Rectangle extends Shape {

  private static String description = "rec·tan·gle\n"
      + "ˈrekˌtaNGɡəl/\n"
      + "noun\n"
      + "a plane figure with four straight sides and four right angles, especially one with unequal adjacent sides, in contrast to a square.";

  public void draw() {

    System.out.printf("%s\n%s", this.getClass().getName(), description);

  }

}public class Circle extends Shape {

  private static String description = "cir·cle"
      + "ˈsərk(ə)l/\n"
      + "noun\n"
      + "1a. round plane figure whose boundary (the circumference) consists of points equidistant from a fixed point (the center).\n"
      + "2. a group of people with shared professions, interests, or acquaintances.\n"
      + "\"she did not normally move in such exalted circles\n"
      + "synonyms: group, set, company, coterie, clique; More \n"
      + "verb\n"
      + "1. move all the way around (someone or something), especially more than once. \n"
      + "\"the two dogs circle each other with hackles raised\n"
      +"synonyms: wheel, move around, revolve, rotate, whirl, spiral\n";
  public void draw() {
    
    System.out.printf("%s\n%s", this.getClass().getName(), description );
  }
}