Singleton design pattern
This pattern makes sure only one object is created and used though out the system.
Create a static instance in the single class
public class SingleObject { //create an object of SingleObject private static SingleObject instance = new SingleObject(); //make the constructor private so that this class cannot be //instantiated private SingleObject(){} //Get the only object available public static SingleObject getInstance(){ return instance; } public void showMessage(){ System.out.println("Hello World!"); } }
Use this instance through the system.
public class SingletonPatternDemo { public static void main(String[] args) { //illegal construct //Compile Time Error: The constructor SingleObject() is not visible //SingleObject object = new SingleObject(); //Get the only object available SingleObject object = SingleObject.getInstance(); //show the message object.showMessage(); } }
Factory design pattern
This pattern helps to create the object without exposing the creation logic to the client and refer to newly created object using a common interface.
The design pattern distinguishes different object type via the parameter.
public class ShapeFactory { //use getShape method to get object of type shape public Shape getShape(String shapeType){ if(shapeType == null){ return null; } if(shapeType.equalsIgnoreCase("CIRCLE")){ return new Circle(); } else if(shapeType.equalsIgnoreCase("RECTANGLE")){ return new Rectangle(); } else if(shapeType.equalsIgnoreCase("SQUARE")){ return new Square(); } return null; } }
public class FactoryPatternDemo { public static void main(String[] args) { ShapeFactory shapeFactory = new ShapeFactory(); //get an object of Circle and call its draw method. Shape shape1 = shapeFactory.getShape("CIRCLE"); //call draw method of Circle shape1.draw(); //get an object of Rectangle and call its draw method. Shape shape2 = shapeFactory.getShape("RECTANGLE"); //call draw method of Rectangle shape2.draw(); //get an object of Square and call its draw method. Shape shape3 = shapeFactory.getShape("SQUARE"); //call draw method of circle shape3.draw(); } }
Comments
Post a Comment