改写设计模式
策略模式（Strategy Pattern）
1. 改写前
a) ValidationStrategy.java
1 public interface ValidationStrategy {2 3 boolean execute(String s);4 5 }b) IsNumeric.java
1 public class IsNumeric implements ValidationStrategy {2 3 public boolean execute(String s) {4 return s.matches("\\d+");5 }6 7 }
c) IsAllLowerCase.java
1 public class IsAllLowerCase implements ValidationStrategy {2 3 public boolean execute(String s) {4 return s.matches("[a-z]+");5 }6 7 }
d) Validator.java
1 public class Validator { 2 private final ValidationStrategy strategy; 3 4 public Validator(ValidationStrategy v) { 5 this.strategy = v; 6 } 7 8 public boolean validate(String s) { 9 return strategy.execute(s);10 }11 }
e) Test.java
1 public class Test { 2 3 public static void main(String[] args) { 4 Validator numericValidator = new Validator(new IsNumeric()); 5 boolean b1 = numericValidator.validate("aaaa"); 6 System.out.println(b1); // false 7 Validator lowerCaseValidator = new Validator(new IsAllLowerCase()); 8 boolean b2 = lowerCaseValidator.validate("bbbb"); 9 System.out.println(b2); // true10 }11 12 }
2.改写后
a) Test.java
1 public class Test { 2 3 public static void main(String[] args) { 4 Validator numericValidator = new Validator((String s) -> s.matches("\\d+")); 5 boolean b1 = numericValidator.validate("aaaa"); 6 System.out.println(b1); // false 7 Validator lowerCaseValidator = new Validator(s -> s.matches("[a-z]+")); 8 boolean b2 = lowerCaseValidator.validate("bbbb"); 9 System.out.println(b2); // true10 }11 12 }
模板方法模式（Template Method Pattern）
1. 改写前
a) Customer.java
1 public class Customer { 2 3 private int id; 4 private String name; 5 6 public Customer(int id, String name) { 7 this.id = id; 8 this.name = name; 9 }10 11 public int getId() {12 return id;13 }14 15 public void setId(int id) {16 this.id = id;17 }18 19 public String getName() {20 return name;21 }22 23 public void setName(String name) {24 this.name = name;25 }26 27 }
b) OnlineBanking.java
1 public abstract class OnlineBanking { 2 3 public void processCustomer(int id) { 4 Customer c = new Customer(id, "Jhon"); 5 makeCustomerHappy(c); 6 } 7 8 abstract void makeCustomerHappy(Customer c); 9 10 }
2.改写后
a) OnlineBankingLambda.java
1 import java.util.function.Consumer; 2 3 public class OnlineBankingLambda { 4 5 public void processCustomer(int id, Consumer<Customer> makeCustomerHappy) { 6 Customer c = new Customer(id, "Jhon"); 7 makeCustomerHappy.accept(c); 8 } 9 10 }
b) Test.java
1 public class Test {2 3 public static void main(String[] args) {4 new OnlineBankingLambda().processCustomer(1337, (Customer c) -> System.out.println("Hello " + c.getName()));5 }6 7 }
观察者模式（Observer Pattern）
1. 改写前
a) Observer.java
1 public interface Observer {2 3 void notify(String tweet);4 5 }b) NYTimes.java
1 public class NYTimes implements Observer {2 3 public void notify(String tweet) {4 if (tweet != null && tweet.contains("money")) {5 System.out.println("Breaking news in NY! " + tweet);6 }7 }8 9 }
c) Guardian.java
1 public class Guardian implements Observer {2 3 public void notify(String tweet) {4 if (tweet != null && tweet.contains("queen")) {5 System.out.println("Yet another news in London... " + tweet);6 }7 }8 9 }
d) LeMonde.java
1 public class LeMonde implements Observer {2 3 public void notify(String tweet) {4 if (tweet != null && tweet.contains("wine")) {5 System.out.println("Today cheese, wine and news! " + tweet);6 }7 }8 9 }
e) Subject.java
1 public interface Subject {2 3 void registerObserver(Observer o);4 5 void notifyObservers(String tweet);6 7 }
f) Feed.java
1 public class Feed implements Subject { 2 3 private final List<Observer> observers = new ArrayList<>(); 4 5 public void registerObserver(Observer o) { 6 this.observers.add(o); 7 } 8 9 public void notifyObservers(String tweet) {10 observers.forEach(o -> o.notify(tweet));11 }12 13 }
g) Test.java
1 public class Test { 2 3 public static void main(String[] args) { 4 Feed f = new Feed(); 5 f.registerObserver(new NYTimes()); 6 f.registerObserver(new Guardian()); 7 f.registerObserver(new LeMonde()); 8 f.notifyObservers("The queen said her favourite book is Java 8 in Action!"); 9 }10 11 }
2.改写后
a) Test.java
1 public class Test { 2 3 public static void main(String[] args) { 4 Feed f = new Feed(); 5 f.registerObserver((String tweet) -> { 6 if (tweet != null && tweet.contains("money")) { 7 System.out.println("Breaking news in NY! " + tweet); 8 } 9 });10 f.registerObserver((tweet) -> {11 if (tweet != null && tweet.contains("queen")) {12 System.out.println("Yet another news in London... " + tweet);13 }14 });15 f.registerObserver((tweet) -> {16 if (tweet != null && tweet.contains("wine")) {17 System.out.println("Today cheese, wine and news! " + tweet);18 }19 });20 f.notifyObservers("The queen said her favourite book is Java 8 in Action!");21 }22 23 }
责任链模式（Chain of Responsibility Pattern）
1. 改写前
a) ProcessingObject.java
1 public abstract class ProcessingObject<T> { 2 3 protected ProcessingObject<T> successor; 4 5 public void setSuccessor(ProcessingObject<T> successor) { 6 this.successor = successor; 7 } 8 9 public T handle(T input) {10 T r = handleWork(input);11 if (successor != null) {12 return successor.handle(r);13 }14 return r;15 }16 17 protected abstract T handleWork(T input);18 }
b) HeaderTextProcessing.java
1 public class HeaderTextProcessing extends ProcessingObject<String> {2 3 public String handleWork(String text) {4 return "From Raoul, Mario and Alan: " + text;5 }6 7 }
c) SpellCheckerProcessing.java
1 public class SpellCheckerProcessing extends ProcessingObject<String> {2 3 public String handleWork(String text) {4 return text.replaceAll("labda", "lambda");5 }6 7 }
d) Test.java
1 public class Test { 2 3 public static void main(String[] args) { 4 ProcessingObject<String> p1 = new HeaderTextProcessing(); 5 ProcessingObject<String> p2 = new SpellCheckerProcessing(); 6 p1.setSuccessor(p2); 7 String result = p1.handle("Aren't labdas really sexy?!!"); 8 System.out.println(result); 9 }10 11 }
2.改写后
a) Test.java
1 public class Test { 2 3 public static void main(String[] args) { 4 UnaryOperator<String> headerProcessing = (String text) -> "From Raoul, Mario and Alan: " + text; 5 UnaryOperator<String> spellCheckerProcessing = (String text) -> text.replaceAll("labda", "lambda"); 6 Function<String, String> pipeline = headerProcessing.andThen(spellCheckerProcessing); 7 String result = pipeline.apply("Aren't labdas really sexy?!!"); 8 System.out.println(result); 9 }10 11 }
简单工厂模式（Simple Factory Pattern）
1. 改写前
a) Product.java
1 public interface Product {2 }b) Loan.java
1 public class Loan implements Product {2 }c) Stock.java
1 public class Stock implements Product {2 }d) Bond.java
1 public class Bond implements Product {2 }e) ProductFactory.java
1 public class ProductFactory { 2 3 public static Product createProduct(String name) { 4 switch (name) { 5 case "loan": 6 return new Loan(); 7 case "stock": 8 return new Stock(); 9 case "bond":10 return new Bond();11 default:12 throw new RuntimeException("No such product " + name);13 }14 }15 16 }
f) Test.java
1 public class Test {2 3 public static void main(String[] args) {4 Product p = ProductFactory.createProduct("loan");5 }6 7 }
2. 改写后
a) ProductFactory.java
1 import java.util.HashMap; 2 import java.util.Map; 3 import java.util.function.Supplier; 4 5 public class ProductFactory { 6 7 final static Map<String, Supplier<Product>> map = new HashMap<>(); 8 9 static {10 map.put("loan", Loan::new);11 map.put("stock", Stock::new);12 map.put("bond", Bond::new);13 }14 15 public static Product createProduct(String name) {16 Supplier<Product> p = map.get(name);17 if (p != null) return p.get();18 throw new IllegalArgumentException("No such product " + name);19 }20 21 }
b) Test.java
1 public class Test {2 3 public static void main(String[] args) {4 Product p = ProductFactory.createProduct("loan");5 }6 7 }
高阶函数与柯里化
1. 高阶函数（Higher-order Function）：满足以下任意一个条件都是高阶函数。
a) 接受至少一个函数作为参数。
b) 返回的结果是一个函数。
2. 柯里化（Currying）：假设有一个函数 f(x, y) ，柯里化就是把多个参数的函数f转化为一个参数的函数g，并且函数g的返回值一个新函数，即 f(x, y) = (g(x))(y) 。
3. 柯里化好处：灵活、复用。
4. 举例
a) 柯里化前
1 public class Test { 2 3 public static double converter(double x, double f, double b) { 4 return x * f + b; 5 } 6 7 public static void main(String[] args) { 8 double gbp = converter(1000, 0.6, 0); 9 System.out.println(gbp);10 }11 12 }
b) 柯里化后
1 public class Test { 2 3 public static DoubleUnaryOperator curriedConverter(double f, double b) { 4 return (double x) -> x * f + b; 5 } 6 7 public static void main(String[] args) { 8 DoubleUnaryOperator convertCtoF = curriedConverter(9.0 / 5, 32); 9 DoubleUnaryOperator convertUSDtoGBP = curriedConverter(0.6, 0);10 DoubleUnaryOperator convertKmtoMi = curriedConverter(0.6214, 0);11 12 double gbp = convertUSDtoGBP.applyAsDouble(1000);13 System.out.println(gbp);14 }15 16 }
作者：netoxi
出处：http://www.cnblogs.com/netoxi
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