Flyweight Design Pattern

The flyweight pattern is used to decrease the number of objects created, therefore reducing memory usage and increasing performance. For example, we have a BuildingMaker that is able to build with four types of materials: brick, stone, wood, and concrete. If we want to build 500 buildings, without using the flyweight pattern, 500 BuildingMaker objects are going to be created, however only four BuildingMaker objects are needed when the flyweight pattern is used.

public class BuildingMaker {
      private String material;

      public BuildingMaker(String m) {
            material = m;
      }

      public void build(int length, int width, int height) {
            System.out.println("Building house with " + material);
            System.out.println("The size of the house is: " + length + "x" + width + "x" + height);
      }
}

1. Without using the flyweight pattern

public class Builder {
      private numberOfBuidings = 500;
      private String[] materials = {"brick", "stone", "wood", "concrete"};
      private int minLength = 100;
      private int minWidth = 50;
      private int minHeight = 25;
   
      public void construct() {
            int len, wid, hei;
            String material;
            for (int i=0; i<numberOfBuidings; i++) {
                  len = minLength + Math.random()*20;
                  wid = minWidth + Math.random()*15;
                  hei = minHeight +  Math.random()*10;
             
                  material = Math.random()*materials.length;
                  BuildingMaker bm = new BuildingMaker(material);//500 BuildingMakers created
                  bm.build(len, wid, hei);
            }
      }
}

2. Using the flyweight pattern

//Create a BuildingMakerFactory to reuse the BuildingMaker set for a material type
public class BuildingMakerFactory {
       //maps material to BuildingMaker
       private HashMap<String, BuildingMaker> buildingMakerMap = new HashMap<String, BuildingMaker>();

      public BuildingMaker getBuildingMaker(String material) {
           BuildingMaker bm = buildingMakerMap.get(material);

            if (bm == null) {
                  bm = new BuildingMaker(material);
                  buildingMakerMap.put(material, bm);
            }

            return bm;
      }
}

public class Builder {
      private numberOfBuidings = 500;
      private String[] materials = {"brick", "stone", "wood", "concrete"};
      private int minLength = 100;
      private int minWidth = 50;
      private int minHeight = 25;

      private BuildingMakerFactory bmf = new BuildingMakerFactory();
   
      public void construct() {
            int len, wid, hei;
            String material;
            for (int i=0; i<numberOfBuidings; i++) {
                  len = minLength + Math.random()*20;
                  wid = minWidth + Math.random()*15;
                  hei = minHeight +  Math.random()*10;
             
                  material = Math.random()*materials.length;
                  BuildingMaker bm = bmf.getBuildingMaker( material);//maximum 4 BuildingMakers created
                  bm.build(len, wid, hei);
            }
      }
}

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