Flyweight Design Pattern
Flyweight design pattern falls under Structural design pattern. This will help to make instances of classes on the fly to improve performance efficiently. This helps to make the instance of the similar class sharing some common state to be reused as much as possible to boost the performance and minimize the memory consumption. The idea behind this pattern is to reduce the load of memory by sharing objects.
The best example is String API in java. In Java, String objects are managed as flyweight objects. Lets see the below example where we can find that what benefits are there to use this design pattern:-
package com.gaurav.designpattern.flyweight;
public class StringPoolTest {
public static void main(String args[]) {
String name = "Gaurav";
String nameVar = "Gaurav";
if (name == nameVar) {
System.out
.println("Both objects are referring to the same memory location in order to minimize memory");
}
}
}
Result:-
Both objects are referring to the same memory location in order to minimize memory
*****Now Consider on the example where we need to create different shapes like circle, rectangle and square in different colors at run-time. Instead of creating multiple instances of same shape type and color, if it has been already created reuse the same. We will see the example below.
Shape.java
package com.gaurav.designpattern.flyweight;
/**
* @author Gaurav
*
*/
public interface Shape {
public String getColor();
public void draw();
}
Circle.java
package com.gaurav.designpattern.flyweight;
/**
* @author Gaurav
*
*/
public class Circle implements Shape{
private String color;
public Circle(String color){
this.color = color;
}
@Override
public String getColor() {
return color;
}
@Override
public void draw() {
System.out.println("Drawing Cirle having color : "+color);
}
}
Rectangle.java
package com.gaurav.designpattern.flyweight;
/**
* @author Gaurav
*
*/
public class Rectangle implements Shape{
private String color;
public Rectangle(String color){
this.color = color;
}
@Override
public String getColor() {
return color;
}
@Override
public void draw() {
System.out.println("Drawing Rectangle having color : "+color);
}
}
Square.java
package com.gaurav.designpattern.flyweight;
/**
* @author Gaurav
*
*/
public class Square implements Shape{
private String color;
public Square(String color){
this.color = color;
}
@Override
public String getColor() {
return color;
}
@Override
public void draw() {
System.out.println("Drawing Square having color : "+color);
}
}
ShapeType.java
package com.gaurav.designpattern.flyweight;
/**
* @author Gaurav
*
*/
public enum ShapeType {
SQUARE,
RECTANGLE,
CIRCLE
}
ShapeFactory.java
package com.gaurav.designpattern.flyweight;
/**
* @author Gaurav
*
*/
import java.util.ArrayList;
import java.util.List;
public class ShapeFactory {
private static ShapeFactory instance;
private List<Shape> shapePool;
private ShapeFactory() {
shapePool = new ArrayList<Shape>(0);
}
public Shape getShape(ShapeType shapeType, String color) {
Shape shape = null;
switch (shapeType) {
case SQUARE:
shape = getShapeUsingPool(shapeType, color);
if (shape == null) {
shape = new Square(color);
shapePool.add(shape);
}
break;
case RECTANGLE:
shape = getShapeUsingPool(shapeType, color);
if (shape == null) {
shape = new Rectangle(color);
shapePool.add(shape);
}
break;
case CIRCLE:
shape = getShapeUsingPool(shapeType, color);
if (shape == null) {
shape = new Circle(color);
shapePool.add(shape);
}
break;
}
return shape;
}
private Shape getShapeUsingPool(ShapeType shapeType, String color) {
Shape shapeP = null;
for (Shape shape : shapePool) {
if (shapeType.equals(ShapeType.SQUARE)) {
if (shape instanceof Square && color.equals(shape.getColor())) {
shapeP = shape;
break;
}
}
if (shapeType.equals(ShapeType.RECTANGLE)) {
if (shape instanceof Rectangle && color.equals(shape.getColor())) {
shapeP = shape;
break;
}
}
if (shapeType.equals(ShapeType.CIRCLE)) {
if (shape instanceof Circle && color.equals(shape.getColor())) {
shapeP = shape;
break;
}
}
}
return shapeP;
}
public int getOverallObjectCreated() {
return shapePool.size();
}
public static ShapeFactory getInstance() {
if (instance == null) {
instance = new ShapeFactory();
}
return instance;
}
}
FlyweightdesignPatternDemo.java
package com.gaurav.designpattern.flyweight;
/**
* @author Gaurav
*
*/
import java.util.Random;
public class FlyweightdesignPatternDemo {
public static void main(String args[]) {
ShapeFactory shapeFactory = ShapeFactory.getInstance();
ShapeType shapeTypes[] = { ShapeType.CIRCLE, ShapeType.RECTANGLE,
ShapeType.SQUARE };
String colors[] = { "RED", "MAGENTA", "PINK", "BLUE", "BLACK", "YELLOW" };
Random random = new Random();
for (int i = 0; i < 15; i++) {
ShapeType shapeType = shapeTypes[random.nextInt(shapeTypes.length)];
String color = colors[random.nextInt(colors.length)];
Shape shape = shapeFactory.getShape(shapeType, color);
shape.draw();
}
System.out
.println("Numbers of overall Objects created after object pool are : "
+ shapeFactory.getOverallObjectCreated());
}
}
Results:
Drawing Cirle having color : BLACK
Drawing Rectangle having color : BLUE
Drawing Cirle having color : BLUE
Drawing Rectangle having color : PINK
Drawing Rectangle having color : RED
Drawing Cirle having color : BLACK
Drawing Square having color : RED
Drawing Cirle having color : MAGENTA
Drawing Square having color : YELLOW
Drawing Rectangle having color : MAGENTA
Drawing Square having color : RED
Drawing Square having color : BLACK
Drawing Cirle having color : BLACK
Drawing Rectangle having color : RED
Drawing Rectangle having color : MAGENTA
Numbers of overall Objects created after object pool are : 10
