7种常见的设计模式讲解【Java基础】

public class Singleton {  
    /* 持有私有静态实例，防止被引用，此处赋值为null，目的是实现延迟加载 */  
    private static Singleton instance = null;  
  
    /* 私有构造方法，防止被实例化 */  
    private Singleton() {}  
  
    /* 1:懒汉式，静态工程方法，创建实例 */  
    public static Singleton getInstance() {  
        if (instance == null) {  
            instance = new Singleton();  
        }  
        return instance;  
    }  
}  

Singleton.getInstance().method();

public class SingletonInner {  
    private static volatile SingletonInner sInst = null;  // <<< 这里添加了 volatile  
  
    /** 
     * 私有的构造函数 
     */  
    private SingletonInner() {}  
  
    public static SingletonInner getInstance() {  
        SingletonInner inst = sInst;  // <<< 在这里创建临时变量
        if (inst == null) {
            synchronized (SingletonInner.class) {
                inst = sInst;
                if (inst == null) {
                    inst = new SingletonInner();
                    sInst = inst;
                }
            }
        }
        return inst;  // <<< 注意这里返回的是临时变量
    }
  
    protected void method() {  
        System.out.println("SingletonInner");  
    }  
}  

Singleton.getInstance().method();

Singleton.getInstance().method();

public class Factory{ //getClass 产生Sample 一般可使用动态类装载装入类。
    public static Sample creator(int which){ 
        if (which==1)
            return new SampleA();
        else if (which==2)
            return new SampleB();
    }
}

Integer a=Integer.valueOf(100); //返回取值为100的Integer对象

//抽象产品角色
public interface Moveable {
    void run();
}
//具体产品角色
public class Plane implements Moveable {
    @Override
    public void run() {
        System.out.println("plane....");
    }
}
//具体产品角色
public class Broom implements Moveable {
    @Override
    public void run() {
        System.out.println("broom.....");
    }
}
 
//抽象工厂
public abstract class VehicleFactory {
    abstract Moveable create();
}
//具体工厂
public class PlaneFactory extends VehicleFactory{
    public Moveable create() {
        return new Plane();
    }
}
//具体工厂
public class BroomFactory extends VehicleFactory{
    public Moveable create() {
        return new Broom();
    }
}
//测试类
public class Test {
    public static void main(String[] args) {
        VehicleFactory factory = new BroomFactory();
        Moveable m = factory.create();
        m.run();
    }
}

public interface Builder {
　  //创建部件A　　比如创建汽车车轮void buildPartA();
　  //创建部件B 比如创建汽车方向盘void buildPartB();
　  //创建部件C 比如创建汽车发动机void buildPartC();
　  //返回最后组装成品结果 (返回最后装配好的汽车)
　  //成品的组装过程不在这里进行,而是转移到下面的Director类中进行.
　  //从而实现了解耦过程和部件
    Product getResult();
}

public class Director {
    private Builder builder;
    public Director( Builder builder ) {
        this.builder = builder;
　  }
　  // 将部件partA partB partC最后组成复杂对象
　  //这里是将车轮 方向盘和发动机组装成汽车的过程
    public void construct() {
        builder.buildPartA();
        builder.buildPartB();
        builder.buildPartC();
    }
}

public interface Product { }

public interface Part { }

/**  
 * Subject(目标，Subject)：    
 * 目标知道它的观察者。可以有任意多个观察者观察同一个目标。  
 * 提供注册和删除观察者对象的接口。  
 */  
public interface Subject {  
    public void attach(Observer mObserver);  
    public void detach(Observer mObserver);        
    public void notice();  
} 

/**  
 * Observer(观察者，Observer)：  
 * 为那些在目标发生改变时需要获得通知的对象定义一个更新接口。   
 */  
public interface Observer {  
    public void update();  
}  

/**  
 * ConcreteSubject(具体目标，Teacher)  
 * 将有关状态存入各ConcreteObserve对象。  
 * 当他的状态发生改变时，向他的各个观察者发出通知。   
 */  
public class Teacher implements Subject{  
     
    private String phone;  
    private Vector students;  
    
    public Teacher(){  
        phone = "";  
        students = new Vector();  
    }  
  
    @Override  
    public void attach(Observer mObserver) {  
        students.add(mObserver);  
    }  
  
    @Override  
    public void detach(Observer mObserver) {  
        students.remove(mObserver);  
    }  
  
    @Override  
    public void notice() {  
        for(int i=0;i<students.size();i++){  
            ((Observer)students.get(i)).update();  
        }  
    }  
  
    public String getPhone() {  
        return phone;  
    }  
  
    public void setPhone(String phone) {  
        this.phone = phone;  
        notice();  
    }  
}

/**  
 * ConcreteObserver(具体观察者, Student)：  
 * 维护一个指向ConcreteSubject对象的引用。  
 * 存储有关状态，这些状态应与目标的状态保持一致。  
 * 实现Observer的更新接口以使自身状态与目标的状态保持一致。  
 */  
public class Student implements Observer{  
  
    private String name;  
    private String phone;  
    private Teacher mTeacher;  
      
    public Student(String name,Teacher t){  
       this.name = name;  
       mTeacher = t;  
    }  
      
    public void show(){  
       System.out.println("Name:"+name+"\nTeacher'sphone:" + phone);  
    }  
      
    @Override  
    public void update() {  
        phone = mTeacher.getPhone();  
    }  
}  

 /**  
 * 观察者(Observer)模式测试类   
 */  
public class ObserverClient {  
    public static void main(String[] args) {  
       Vector students = new Vector();  
       Teacher t = new Teacher();  
       for(int i= 0;i<10;i++){  
           Student st = new Student("Andy.Chen"+i,t);  
           students.add(st);  
           t.attach(st);  
       }  
         
       System.out.println("Welcome to Andy.Chen Blog!" +"\n"   
                   +"Observer Patterns." +"\n"  
                   +"-------------------------------");  
         
       t.setPhone("12345678");  
       for(int i=0;i<3;i++)  
           ((Student)students.get(i)).show();  
         
       t.setPhone("87654321");  
       for(int i=0;i<3;i++)  
           ((Student)students.get(i)).show();  
    }  
} 

Welcome to Andy.Chen Blog!  
Observer Patterns.  
-------------------------------  
Name:Andy.Chen0  
Teacher'sphone:12345678  
Name:Andy.Chen1  
Teacher'sphone:12345678  
Name:Andy.Chen2  
Teacher'sphone:12345678  
Name:Andy.Chen0  
Teacher'sphone:87654321  
Name:Andy.Chen1  
Teacher'sphone:87654321  
Name:Andy.Chen2  
Teacher'sphone:87654321  

public interface Target {
    /**
     * 这是源类Adaptee也有的方法
     */
    public void sampleOperation1(); 
    /**
     * 这是源类Adapteee没有的方法
     */
    public void sampleOperation2(); 
}

public class Adapter extends Adaptee implements Target {
    /**
     * 由于源类Adaptee没有方法sampleOperation2()
     * 因此适配器补充上这个方法
     */
    @Override
    public void sampleOperation2() {
        //写相关的代码
    }
}

public interface Target {
    /**
     * 这是源类Adaptee也有的方法
     */
    public void sampleOperation1(); 
    /**
     * 这是源类Adapteee没有的方法
     */
    public void sampleOperation2(); 
}
 
public class Adaptee {
    public void sampleOperation1(){}
}

public class Adapter {
    private Adaptee adaptee;
    public Adapter(Adaptee adaptee){
        this.adaptee = adaptee;
    }
    /**
     * 源类Adaptee有方法sampleOperation1
     * 因此适配器类直接委派即可
     */
    public void sampleOperation1(){
        this.adaptee.sampleOperation1();
    }
    /**
     * 源类Adaptee没有方法sampleOperation2
     * 因此由适配器类需要补充此方法
     */
    public void sampleOperation2(){
        //写相关的代码
    }
}

public class ForumProxy implements Forum {
    private ForumPermissions permissions;
    private Forum forum;
    this.authorization = authorization;
 
    public ForumProxy(Forum forum, Authorization authorization,ForumPermissions permissions){
        this.forum = forum;
        this.authorization = authorization;
        this.permissions = permissions;
    }
    .....
    public void setName(String name) throws UnauthorizedException,
        ForumAlreadyExistsException{
        //只有是系统或论坛管理者才可以修改名称
      if (permissions.isSystemOrForumAdmin()) {
        forum.setName(name);
      }
　　  else {
　　　 throw new UnauthorizedException();
　　  }
    }
    ...
 
} 

public class DbForum implements Forum, Cacheable {
    ...
    public void setName(String name) throws ForumAlreadyExistsException {
　　....
        this.name = name;
　　     //这里真正将新名称保存到数据库中
　　     saveToDb();
　　....
    }
    ...
}

public interface Component {    
    void show();
}

public class Person implements Component{
    private String name;
    public String getName() {
        return name;
    }
 
    public void setName(String name) {
        this.name = name;
    }
 
    public Person(String name){
        this.name = name;
    }
 
    @Override
    public void show() {
        System.out.println("装扮的" + name);
    }
}

public class Decorator implements Component{
    private Component mComponent;
    public void decoratorObj(Component component){
        mComponent = component;
    }
 
    @Override
    public void show() {
        if(mComponent != null){
            mComponent.show();
        }
    }
}

/** 牛仔裤 */
public class Jeans extends Decorator {
    @Override
    public void show(){
        System.out.println("穿牛仔裤");
        super.show();
    }
    
}

/**
 * 装饰模式测试客户端
 */
public class DecoratorClient {
    public static void main(String[] args) {
        System.out.println("Welcome to Andy.Chen Blog!" +"\n" 
                   +"Decorator Patterns." +"\n");
        
        Person mPerson = new Person("Andy");
        
        Sandal mSandal = new Sandal();
        Jeans mJeans = new Jeans();
        TShirt mShirt = new TShirt();
        
        mShirt.decoratorObj(mPerson);
        mJeans.decoratorObj(mShirt);
        mSandal.decoratorObj(mJeans);
        mSandal.show(); 
    }
}

Welcome to Andy.Chen Blog!
Decorator Patterns.
  
穿凉鞋
穿牛仔裤
穿T-Shirt
装扮的Andy