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Head First设计模式学习笔记

大家好，我是微赚淘客系统3.0的小编，是个冬天不穿秋裤，天冷也要风度的程序猿！

一、策略模式

策略模式定义了算法族，分别封装起来，让它们之间可以互相替换，此模式让算法的变化独立于使用算法的客户。

package cn.juwatech.strategy;interface QuackBehavior {void quack();
}class Quack implements QuackBehavior {public void quack() {System.out.println("Quack");}
}class Squeak implements QuackBehavior {public void quack() {System.out.println("Squeak");}
}abstract class Duck {QuackBehavior quackBehavior;public void performQuack() {quackBehavior.quack();}public void setQuackBehavior(QuackBehavior qb) {this.quackBehavior = qb;}abstract void display();
}class MallardDuck extends Duck {public MallardDuck() {quackBehavior = new Quack();}void display() {System.out.println("I'm a Mallard Duck");}
}public class StrategyPatternDemo {public static void main(String[] args) {Duck mallard = new MallardDuck();mallard.performQuack();mallard.setQuackBehavior(new Squeak());mallard.performQuack();}
}

二、观察者模式

观察者模式定义了一种一对多的依赖关系，让多个观察者对象同时监听某一个主题对象。当主题对象发生变化时，它的所有依赖者（观察者）都会收到通知并更新。

package cn.juwatech.observer;import java.util.ArrayList;
import java.util.List;interface Observer {void update(float temp, float humidity, float pressure);
}interface Subject {void registerObserver(Observer o);void removeObserver(Observer o);void notifyObservers();
}class WeatherData implements Subject {private List<Observer> observers;private float temperature;private float humidity;private float pressure;public WeatherData() {observers = new ArrayList<>();}public void registerObserver(Observer o) {observers.add(o);}public void removeObserver(Observer o) {observers.remove(o);}public void notifyObservers() {for (Observer observer : observers) {observer.update(temperature, humidity, pressure);}}public void measurementsChanged() {notifyObservers();}public void setMeasurements(float temperature, float humidity, float pressure) {this.temperature = temperature;this.humidity = humidity;this.pressure = pressure;measurementsChanged();}
}class CurrentConditionsDisplay implements Observer {private float temperature;private float humidity;private Subject weatherData;public CurrentConditionsDisplay(Subject weatherData) {this.weatherData = weatherData;weatherData.registerObserver(this);}public void update(float temp, float humidity, float pressure) {this.temperature = temp;this.humidity = humidity;display();}public void display() {System.out.println("Current conditions: " + temperature + "F degrees and " + humidity + "% humidity");}
}public class ObserverPatternDemo {public static void main(String[] args) {WeatherData weatherData = new WeatherData();CurrentConditionsDisplay currentDisplay = new CurrentConditionsDisplay(weatherData);weatherData.setMeasurements(80, 65, 30.4f);weatherData.setMeasurements(82, 70, 29.2f);}
}

三、装饰者模式

装饰者模式动态地将责任附加到对象上。若要扩展功能，装饰者提供了比继承更有弹性的替代方案。

package cn.juwatech.decorator;abstract class Beverage {String description = "Unknown Beverage";public String getDescription() {return description;}public abstract double cost();
}class Espresso extends Beverage {public Espresso() {description = "Espresso";}public double cost() {return 1.99;}
}abstract class CondimentDecorator extends Beverage {public abstract String getDescription();
}class Mocha extends CondimentDecorator {Beverage beverage;public Mocha(Beverage beverage) {this.beverage = beverage;}public String getDescription() {return beverage.getDescription() + ", Mocha";}public double cost() {return .20 + beverage.cost();}
}public class DecoratorPatternDemo {public static void main(String[] args) {Beverage beverage = new Espresso();System.out.println(beverage.getDescription() + " $" + beverage.cost());beverage = new Mocha(beverage);System.out.println(beverage.getDescription() + " $" + beverage.cost());}
}

四、工厂模式

工厂模式通过定义一个创建对象的接口，让子类决定实例化哪一个类。

package cn.juwatech.factory;abstract class Pizza {String name;void prepare() {System.out.println("Preparing " + name);}void bake() {System.out.println("Baking " + name);}void cut() {System.out.println("Cutting " + name);}void box() {System.out.println("Boxing " + name);}public String getName() {return name;}
}class CheesePizza extends Pizza {public CheesePizza() {name = "Cheese Pizza";}
}class GreekPizza extends Pizza {public GreekPizza() {name = "Greek Pizza";}
}abstract class PizzaStore {public Pizza orderPizza(String type) {Pizza pizza = createPizza(type);pizza.prepare();pizza.bake();pizza.cut();pizza.box();return pizza;}protected abstract Pizza createPizza(String type);
}class SimplePizzaFactory extends PizzaStore {protected Pizza createPizza(String type) {Pizza pizza = null;if (type.equals("cheese")) {pizza = new CheesePizza();} else if (type.equals("greek")) {pizza = new GreekPizza();}return pizza;}
}public class FactoryPatternDemo {public static void main(String[] args) {PizzaStore store = new SimplePizzaFactory();Pizza pizza = store.orderPizza("cheese");System.out.println("Ordered a " + pizza.getName() + "\n");pizza = store.orderPizza("greek");System.out.println("Ordered a " + pizza.getName() + "\n");}
}

本文著作权归聚娃科技微赚淘客系统开发者团队，转载请注明出处！