Notes

package factorypattern;

public class FactoryPatternDemoPizza {
public static void main(String[] args) {
SimplePizzaFactory simplePizzaFactory = new SimplePizzaFactory();
Pizza pizza = simplePizzaFactory.createPizza("cheese");
pizza.prepare();
simplePizzaFactory.createPizza("pepperoni").prepare();
}
}

interface Pizza{
void prepare();
}

class CheesePizza implements Pizza{

@Override
public void prepare() {
System.out.println("Cheese Pizza Prepared");
}
}

class PepperoniPizza implements Pizza{

@Override
public void prepare() {
System.out.println("Pepperoni Pizza Prepared");

}
}

class VeggiePizza implements Pizza{

@Override
public void prepare() {
System.out.println("Veggie Pizza Prepared");
}
}

class SimplePizzaFactory {
public Pizza createPizza(String type) {
Pizza pizza = null;
if (type.equals("cheese")) {
pizza = new CheesePizza();
} else if (type.equals("pepperoni")) {
pizza = new PepperoniPizza();
} else if (type.equals("veggie")) {
pizza = new VeggiePizza();
}
return pizza;
}
}


singleton
package singletonpattern;

class SingleObject {
private static SingleObject instance = new SingleObject();
private SingleObject(){}

public static SingleObject getInstance(){
return instance;
}

public void showMessage(){
System.out.println("Hello World!");
}
}

public class SingletonPatternDemo {
public static void main(String[] args) {

//illegal construct
//Compile Time Error: The constructor SingleObject() is not visible
//SingleObject object = new SingleObject();

SingleObject object = SingleObject.getInstance();
object.showMessage();
}
}



package strategypattern;

public class StrategyPatternDemo {
public static void main(String[] args) {
Context context = new Context(new OperationAdd());
System.out.println(context.executeStrategy(5,4));
}
}

class Context {
private IStrategy strategy;
public Context(IStrategy strategy){
this.strategy = strategy;
}
public int executeStrategy(int num1, int num2){
return strategy.doOperation(num1,num2);
}
}

interface IStrategy {
int doOperation(int a, int b);
}

class OperationAdd implements IStrategy {

@Override
public int doOperation(int a, int b) {
return a+b;
}
}

class OperationSubstruct implements IStrategy {

@Override
public int doOperation(int a, int b) {
return a-b;
}
}