设计模式

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Sean Yu 11月 25, 2020
  • 在其它设备中阅读本文章

http://c.biancheng.net/view/8385.html 这篇文章对Java设计模式有十分全面的介绍。本文结合网上资料和自己经验总结一些设计模式的案例。

单例模式

简单的

private static Singleton instance;

    private Singleton() {
    }

    public static Singleton getInstance() {
        if (instance == null)
            instance = new Singleton();

        return instance;
    }

双重检查

为什么要双重检查
如果不加内层检查，两个线程可以同时进入if创建实例
如果不加外层检查，会重复上锁影响性能


// 注意一定要用volatile来避免指令重排
private volatile static Singleton instance;

public static Singleton getInstance() {
        if (instance == null) {
            synchronized (Singleton.class) {
                if (instance == null)
                    instance = new Singleton();
            }
        }

        return instance;
    }

静态内部类

class Singleton {
    public static Singleton instance;

    private static class SingletonWrapper {
        static Singleton instance = new Singleton();
    }

    private Singleton() {

    }

    public static Singleton getInstance() {
        return SingletonWrapper.instance;
    }
}

枚举

public class Main {
    public static void main(String[] args) {
        Singleton.INSTANCE.sayHello();
    }
}

enum Singleton {
    INSTANCE;

    public void sayHello() {
        System.out.println("hello");
    }
}

工厂模式

简单工厂

image.png

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

    //抽象产品
    public interface Product {
        void show();
    }

    //具体产品：ProductA
    static class ConcreteProduct1 implements Product {
        public void show() {
            System.out.println("具体产品1显示...");
        }
    }

    //具体产品：ProductB
    static class ConcreteProduct2 implements Product {
        public void show() {
            System.out.println("具体产品2显示...");
        }
    }

    final class Const {
        static final int PRODUCT_A = 0;
        static final int PRODUCT_B = 1;
        static final int PRODUCT_C = 2;
    }

    static class SimpleFactory {
        public static Product makeProduct(int kind) {
            switch (kind) {
                case Const.PRODUCT_A:
                    return new ConcreteProduct1();
                case Const.PRODUCT_B:
                    return new ConcreteProduct2();
            }
            return null;
        }
    }
}

简单工厂模式没啥好说的，因为它太简单了。代码直接略过。唯一要说的是提供一种spring下的工厂模式实现思路，可以把一个接口的所有实现类都注册成bean，然后通过不同bean的名字来实现一个简单工厂，我在做分布式锁的时候用过这种方式，代码更简洁优雅。详见这里

工厂方法

image.png

package FactoryMethod;

public class AbstractFactoryTest {
    public static void main(String[] args) {
        try {
            Product a;
            AbstractFactory af;
            af = (AbstractFactory) ReadXML1.getObject();
            a = af.newProduct();
            a.show();
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
    }
}

//抽象产品：提供了产品的接口
interface Product {
    public void show();
}

//具体产品1：实现抽象产品中的抽象方法
class ConcreteProduct1 implements Product {
    public void show() {
        System.out.println("具体产品1显示...");
    }
}

//具体产品2：实现抽象产品中的抽象方法
class ConcreteProduct2 implements Product {
    public void show() {
        System.out.println("具体产品2显示...");
    }
}

//抽象工厂：提供了厂品的生成方法
interface AbstractFactory {
    public Product newProduct();
}

//具体工厂1：实现了厂品的生成方法
class ConcreteFactory1 implements AbstractFactory {
    public Product newProduct() {
        System.out.println("具体工厂1生成-->具体产品1...");
        return new ConcreteProduct1();
    }
}

//具体工厂2：实现了厂品的生成方法
class ConcreteFactory2 implements AbstractFactory {
    public Product newProduct() {
        System.out.println("具体工厂2生成-->具体产品2...");
        return new ConcreteProduct2();
    }
}

抽象工厂

image.png

package AbstractFactory;

import java.awt.*;
import javax.swing.*;

public class FarmTest {
    public static void main(String[] args) {
        try {
            Farm f;
            Animal a;
            Plant p;
            f = (Farm) ReadXML.getObject();
            a = f.newAnimal();
            p = f.newPlant();
            a.show();
            p.show();
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
    }
}

//抽象产品：动物类
interface Animal {
    public void show();
}

//具体产品：马类
class Horse implements Animal {
    JScrollPane sp;
    JFrame jf = new JFrame("抽象工厂模式测试");

    public Horse() {
        Container contentPane = jf.getContentPane();
        JPanel p1 = new JPanel();
        p1.setLayout(new GridLayout(1, 1));
        p1.setBorder(BorderFactory.createTitledBorder("动物：马"));
        sp = new JScrollPane(p1);
        contentPane.add(sp, BorderLayout.CENTER);
        JLabel l1 = new JLabel(new ImageIcon("src/A_Horse.jpg"));
        p1.add(l1);
        jf.pack();
        jf.setVisible(false);
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);//用户点击窗口关闭
    }

    public void show() {
        jf.setVisible(true);
    }
}

//具体产品：牛类
class Cattle implements Animal {
    JScrollPane sp;
    JFrame jf = new JFrame("抽象工厂模式测试");

    public Cattle() {
        Container contentPane = jf.getContentPane();
        JPanel p1 = new JPanel();
        p1.setLayout(new GridLayout(1, 1));
        p1.setBorder(BorderFactory.createTitledBorder("动物：牛"));
        sp = new JScrollPane(p1);
        contentPane.add(sp, BorderLayout.CENTER);
        JLabel l1 = new JLabel(new ImageIcon("src/A_Cattle.jpg"));
        p1.add(l1);
        jf.pack();
        jf.setVisible(false);
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);//用户点击窗口关闭
    }

    public void show() {
        jf.setVisible(true);
    }
}

//抽象产品：植物类
interface Plant {
    public void show();
}

//具体产品：水果类
class Fruitage implements Plant {
    JScrollPane sp;
    JFrame jf = new JFrame("抽象工厂模式测试");

    public Fruitage() {
        Container contentPane = jf.getContentPane();
        JPanel p1 = new JPanel();
        p1.setLayout(new GridLayout(1, 1));
        p1.setBorder(BorderFactory.createTitledBorder("植物：水果"));
        sp = new JScrollPane(p1);
        contentPane.add(sp, BorderLayout.CENTER);
        JLabel l1 = new JLabel(new ImageIcon("src/P_Fruitage.jpg"));
        p1.add(l1);
        jf.pack();
        jf.setVisible(false);
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);//用户点击窗口关闭
    }

    public void show() {
        jf.setVisible(true);
    }
}

//具体产品：蔬菜类
class Vegetables implements Plant {
    JScrollPane sp;
    JFrame jf = new JFrame("抽象工厂模式测试");

    public Vegetables() {
        Container contentPane = jf.getContentPane();
        JPanel p1 = new JPanel();
        p1.setLayout(new GridLayout(1, 1));
        p1.setBorder(BorderFactory.createTitledBorder("植物：蔬菜"));
        sp = new JScrollPane(p1);
        contentPane.add(sp, BorderLayout.CENTER);
        JLabel l1 = new JLabel(new ImageIcon("src/P_Vegetables.jpg"));
        p1.add(l1);
        jf.pack();
        jf.setVisible(false);
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);//用户点击窗口关闭
    }

    public void show() {
        jf.setVisible(true);
    }
}

//抽象工厂：农场类
interface Farm {
    public Animal newAnimal();

    public Plant newPlant();
}

//具体工厂：韶关农场类
class SGfarm implements Farm {
    public Animal newAnimal() {
        System.out.println("新牛出生！");
        return new Cattle();
    }

    public Plant newPlant() {
        System.out.println("蔬菜长成！");
        return new Vegetables();
    }
}

//具体工厂：上饶农场类
class SRfarm implements Farm {
    public Animal newAnimal() {
        System.out.println("新马出生！");
        return new Horse();
    }

    public Plant newPlant() {
        System.out.println("水果长成！");
        return new Fruitage();
    }
}

建造者模式（Bulider模式）

image.png

class Product
{
    private String partA;
    private String partB;
    private String partC;
    public void setPartA(String partA)
    {
        this.partA=partA;
    }
    public void setPartB(String partB)
    {
        this.partB=partB;
    }
    public void setPartC(String partC)
    {
        this.partC=partC;
    }
    public void show()
    {
        //显示产品的特性
    }
}

abstract class Builder
{
    //创建产品对象
    protected Product product=new Product();
    public abstract void buildPartA();
    public abstract void buildPartB();
    public abstract void buildPartC();
    //返回产品对象
    public Product getResult()
    {
        return product;
    }
}

public class ConcreteBuilder extends Builder
{
    public void buildPartA()
    {
        product.setPartA("建造 PartA");
    }
    public void buildPartB()
    {
        product.setPartB("建造 PartB");
    }
    public void buildPartC()
    {
        product.setPartC("建造 PartC");
    }
}

class Director
{
    private Builder builder;
    public Director(Builder builder)
    {
        this.builder=builder;
    }
    //产品构建与组装方法
    public Product construct()
    {
        builder.buildPartA();
        builder.buildPartB();
        builder.buildPartC();
        return builder.getResult();
    }
}

public class Client
{
    public static void main(String[] args)
    {
        Builder builder=new ConcreteBuilder();
        Director director=new Director(builder);
        Product product=director.construct();
        product.show();
    }
}

代理模式

image.png

package proxy;
public class ProxyTest {
    public static void main(String[] args) {
        Proxy proxy = new Proxy();
        proxy.Request();
    }
}
//抽象主题
interface Subject {
    void Request();
}
//真实主题
class RealSubject implements Subject {
    public void Request() {
        System.out.println("访问真实主题方法...");
    }
}
//代理
class Proxy implements Subject {
    private RealSubject realSubject;
    public void Request() {
        if (realSubject == null) {
            realSubject = new RealSubject();
        }
        preRequest();
        realSubject.Request();
        postRequest();
    }
    public void preRequest() {
        System.out.println("访问真实主题之前的预处理。");
    }
    public void postRequest() {
        System.out.println("访问真实主题之后的后续处理。");
    }
}

适配器模式（Adapter模式）

类适配器模式

接口实现类调用另一个子类的方法
image.png

package adapter;
//目标接口
interface Target
{
    public void request();
}
//适配者接口
class Adaptee
{
    public void specificRequest()
    {       
        System.out.println("适配者中的业务代码被调用！");
    }
}
//类适配器类
class ClassAdapter extends Adaptee implements Target
{
    public void request()
    {
        specificRequest();
    }
}
//客户端代码
public class ClassAdapterTest
{
    public static void main(String[] args)
    {
        System.out.println("类适配器模式测试：");
        Target target = new ClassAdapter();
        target.request();
    }
}

对象适配器模式

用适配对象去实现接口，调用适配器方法
image.png

package adapter;
//对象适配器类
class ObjectAdapter implements Target
{
    private Adaptee adaptee;
    public ObjectAdapter(Adaptee adaptee)
    {
        this.adaptee=adaptee;
    }
    public void request()
    {
        adaptee.specificRequest();
    }
}
//客户端代码
public class ObjectAdapterTest
{
    public static void main(String[] args)
    {
        System.out.println("对象适配器模式测试：");
        Adaptee adaptee = new Adaptee();
        Target target = new ObjectAdapter(adaptee);
        target.request();
    }
}

桥接模式（Bridge模式）

通过一个抽象类对一个接口的引用实现桥接

image.png

package bridge;
public class BridgeTest
{
    public static void main(String[] args)
    {
        Implementor imple=new ConcreteImplementorA();
        Abstraction abs=new RefinedAbstraction(imple);
        abs.Operation();
    }
}
//实现化角色
interface Implementor
{
    public void OperationImpl();
}
//具体实现化角色
class ConcreteImplementorA implements Implementor
{
    public void OperationImpl()
    {
        System.out.println("具体实现化(Concrete Implementor)角色被访问" );
    }
}
//抽象化角色
abstract class Abstraction
{
   protected Implementor imple;
   protected Abstraction(Implementor imple)
   {
       this.imple=imple;
   }
   public abstract void Operation();   
}
//扩展抽象化角色
class RefinedAbstraction extends Abstraction
{
   protected RefinedAbstraction(Implementor imple)
   {
       super(imple);
   }
   public void Operation()
   {
       System.out.println("扩展抽象化(Refined Abstraction)角色被访问" );
       imple.OperationImpl();
   }
}

装饰（Decorator）模式

装饰者和具体实现，实现同一个接口，装饰者为借口方法提供额外功能

image.png

package decorator;
public class DecoratorPattern
{
    public static void main(String[] args)
    {
        Component p=new ConcreteComponent();
        p.operation();
        System.out.println("---------------------------------");
        Component d=new ConcreteDecorator(p);
        d.operation();
    }
}
//抽象构件角色
interface  Component
{
    public void operation();
}
//具体构件角色
class ConcreteComponent implements Component
{
    public ConcreteComponent()
    {
        System.out.println("创建具体构件角色");       
    }   
    public void operation()
    {
        System.out.println("调用具体构件角色的方法operation()");           
    }
}
//抽象装饰角色
class Decorator implements Component
{
    private Component component;   
    public Decorator(Component component)
    {
        this.component=component;
    }   
    public void operation()
    {
        component.operation();
    }
}
//具体装饰角色
class ConcreteDecorator extends Decorator
{
    public ConcreteDecorator(Component component)
    {
        super(component);
    }   
    public void operation()
    {
        super.operation();
        addedFunction();
    }
    public void addedFunction()
    {
        System.out.println("为具体构件角色增加额外的功能addedFunction()");           
    }
}

组合模式

image.png

package composite;
import java.util.ArrayList;
public class ShoppingTest {
    public static void main(String[] args) {
        float s = 0;
        Bags BigBag, mediumBag, smallRedBag, smallWhiteBag;
        Goods sp;
        BigBag = new Bags("大袋子");
        mediumBag = new Bags("中袋子");
        smallRedBag = new Bags("红色小袋子");
        smallWhiteBag = new Bags("白色小袋子");
        sp = new Goods("婺源特产", 2, 7.9f);
        smallRedBag.add(sp);
        sp = new Goods("婺源地图", 1, 9.9f);
        smallRedBag.add(sp);
        sp = new Goods("韶关香菇", 2, 68);
        smallWhiteBag.add(sp);
        sp = new Goods("韶关红茶", 3, 180);
        smallWhiteBag.add(sp);
        sp = new Goods("景德镇瓷器", 1, 380);
        mediumBag.add(sp);
        mediumBag.add(smallRedBag);
        sp = new Goods("李宁牌运动鞋", 1, 198);
        BigBag.add(sp);
        BigBag.add(smallWhiteBag);
        BigBag.add(mediumBag);
        System.out.println("您选购的商品有：");
        BigBag.show();
        s = BigBag.calculation();
        System.out.println("要支付的总价是：" + s + "元");
    }
}
//抽象构件：物品
interface Articles {
    public float calculation(); //计算
    public void show();
}
//树叶构件：商品
class Goods implements Articles {
    private String name;     //名字
    private int quantity;    //数量
    private float unitPrice; //单价
    public Goods(String name, int quantity, float unitPrice) {
        this.name = name;
        this.quantity = quantity;
        this.unitPrice = unitPrice;
    }
    public float calculation() {
        return quantity * unitPrice;
    }
    public void show() {
        System.out.println(name + "(数量：" + quantity + "，单价：" + unitPrice + "元)");
    }
}
//树枝构件：袋子
class Bags implements Articles {
    private String name;     //名字  
    private ArrayList<Articles> bags = new ArrayList<Articles>();
    public Bags(String name) {
        this.name = name;
    }
    public void add(Articles c) {
        bags.add(c);
    }
    public void remove(Articles c) {
        bags.remove(c);
    }
    public Articles getChild(int i) {
        return bags.get(i);
    }
    public float calculation() {
        float s = 0;
        for (Object obj : bags) {
            s += ((Articles) obj).calculation();
        }
        return s;
    }
    public void show() {
        for (Object obj : bags) {
            ((Articles) obj).show();
        }
    }
}

模板方法（Template Method）模式

image.png

public class TemplateMethodPattern {
    public static void main(String[] args) {
        AbstractClass tm = new ConcreteClass();
        tm.TemplateMethod();
    }
}
//抽象类
abstract class AbstractClass {
    //模板方法
    public void TemplateMethod() {
        SpecificMethod();
        abstractMethod1();
        abstractMethod2();
    }
    //具体方法
    public void SpecificMethod() {
        System.out.println("抽象类中的具体方法被调用...");
    }
    //抽象方法1
    public abstract void abstractMethod1();
    //抽象方法2
    public abstract void abstractMethod2();
}
//具体子类
class ConcreteClass extends AbstractClass {
    public void abstractMethod1() {
        System.out.println("抽象方法1的实现被调用...");
    }
    public void abstractMethod2() {
        System.out.println("抽象方法2的实现被调用...");
    }
}

责任链（Chain of Responsibility）模式

image.png

package chainOfResponsibility;
public class ChainOfResponsibilityPattern {
    public static void main(String[] args) {
        //组装责任链
        Handler handler1 = new ConcreteHandler1();
        Handler handler2 = new ConcreteHandler2();
        handler1.setNext(handler2);
        //提交请求
        handler1.handleRequest("two");
    }
}
//抽象处理者角色
abstract class Handler {
    private Handler next;
    public void setNext(Handler next) {
        this.next = next;
    }
    public Handler getNext() {
        return next;
    }
    //处理请求的方法
    public abstract void handleRequest(String request);
}
//具体处理者角色1
class ConcreteHandler1 extends Handler {
    public void handleRequest(String request) {
        if (request.equals("one")) {
            System.out.println("具体处理者1负责处理该请求！");
        } else {
            if (getNext() != null) {
                getNext().handleRequest(request);
            } else {
                System.out.println("没有人处理该请求！");
            }
        }
    }
}
//具体处理者角色2
class ConcreteHandler2 extends Handler {
    public void handleRequest(String request) {
        if (request.equals("two")) {
            System.out.println("具体处理者2负责处理该请求！");
        } else {
            if (getNext() != null) {
                getNext().handleRequest(request);
            } else {
                System.out.println("没有人处理该请求！");
            }
        }
    }
}

观察者模式（Observer模式）

image.png

package net.biancheng.c.observer;
import java.util.*;
public class ObserverPattern {
    public static void main(String[] args) {
        Subject subject = new ConcreteSubject();
        Observer obs1 = new ConcreteObserver1();
        Observer obs2 = new ConcreteObserver2();
        subject.add(obs1);
        subject.add(obs2);
        subject.notifyObserver();
    }
}
//抽象目标
abstract class Subject {
    protected List<Observer> observers = new ArrayList<Observer>();
    //增加观察者方法
    public void add(Observer observer) {
        observers.add(observer);
    }
    //删除观察者方法
    public void remove(Observer observer) {
        observers.remove(observer);
    }
    public abstract void notifyObserver(); //通知观察者方法
}
//具体目标
class ConcreteSubject extends Subject {
    public void notifyObserver() {
        System.out.println("具体目标发生改变...");
        System.out.println("--------------");
        for (Object obs : observers) {
            ((Observer) obs).response();
        }
    }
}
//抽象观察者
interface Observer {
    void response(); //反应
}
//具体观察者1
class ConcreteObserver1 implements Observer {
    public void response() {
        System.out.println("具体观察者1作出反应！");
    }
}
//具体观察者1
class ConcreteObserver2 implements Observer {
    public void response() {
        System.out.println("具体观察者2作出反应！");
    }
}