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组合模式及单例模式

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发布于: 2020 年 10 月 04 日
组合模式及单例模式



组合模式





将一组对象组织（Compose）成树形结构，以表示一种“部分 - 整体”的层次结构。



示例：文本打印



组合设计模式模拟窗口显示



Component.java



public interface  Component{
    public  String getName();
    public  void print();
}




Composite.java



import java.util.ArrayList;
import java.util.List;

public class Composite  implements Component{
    private String name;
    private List<Component> componentList = new ArrayList<Component>();


    public Composite(String name){
        this.name = name;
    }

    public String getName(){
        return this.name;
    }

    public void add(Component component){
        componentList.add(component);
    }

    public void print() {
        System.out.println(name);
        for (Component component : componentList) {
            component.print();
        }
    }

}


Leaf.java

public class Leaf implements Component {

    private String name;

    public Leaf(String name) {

        this.name = name;
    }


    public String getName() {

        return this.name;
    }

    public void print() {
        System.out.println(name);
    }

}



Windows.java

public class Windows {


    public static void print(){
        Composite winform = new Composite("WinForm(WINDOW窗口)");
        Leaf picture = new Leaf("Picture(LOGO图片)");
        Leaf loginbutton = new Leaf("Button(登录)");
        Leaf registerbutton = new Leaf("Button(注册)");

        winform.add(picture);
        winform.add(loginbutton);
        winform.add(registerbutton);

        Composite frame = new Composite("Frame(FRAME1)");
        Leaf label = new Leaf("Lable(用户名)");
        Leaf textbox = new Leaf("Text(文本框)");
        Leaf password = new Leaf("PasswordBox(密码框)");
        Leaf checkbox = new Leaf("CheckBox(复选框)");
        Leaf textbox2 = new Leaf("TextBox(记住用户名)");
        Leaf linklabel = new Leaf("Linkable(忘记密码)");

        frame.add(label);
        frame.add(textbox);
        frame.add(password);
        frame.add(checkbox);
        frame.add(textbox2);
        frame.add(linklabel);

        winform.add(frame);
        winform.print();

    }
    
    public static void main(String[] args) {
        print();
    }

}




示例：java swing图形打印





Button.java

import javax.swing.*;
public class Button extends JButton {

    public void print() {
        System.out.println(getText());
    }
    public Button(String text) {
        super(text, null);
        print();
    }
}



CheckBox.java

import javax.swing.*;

public class CheckBox extends JCheckBox {
    public void print() {
        System.out.println(getText());
    }

    public CheckBox (String text) {
        super(text, null, false);
        print();
    }

}




Frame.java

import javax.swing.*;

public class Frame extends JPanel {
    private String name;
    public void print() {
        System.out.println(name);
    }
    public Frame(String text) {
        super(true);
        this.name = text;
        print();
    }
}




Label.java

import javax.swing.*;

public class Lable extends JLabel {
    //private String name;
    public void print() {
        System.out.println(getText());
    }
    public Lable(String text) {
        super(text, null, LEADING);
        //this.name = text;
        print();
    }


}



Linkable.java

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

public class Linkable extends JLabel {

    public void print() {
        System.out.println(getText());
    }
    public Linkable(String text) {
        super(text, null, LEADING);
        this.setForeground(Color.BLUE.darker());
        this.setCursor(Cursor.getPredefinedCursor(Cursor.HAND_CURSOR));
        print();
    }

}




Picture.java

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

public class Picture extends JLabel{
    //private String name;
    public void print() {
        System.out.println(getText());
    }

    public Picture(String text, String ImageName) {
        super(text, null, LEADING);
        Image image = new ImageIcon(ImageName).getImage();
        setIcon(new ImageIcon(image));
        //his.name = text;
        print();
    }
}




TextBox.java



import javax.swing.*;

public class TextBox extends JTextField {
    //JTextComponent 有同名函数
    public void printbox() {
        System.out.println(getText());
    }
    public TextBox(String text) {
        super(null, text, 0);
        printbox();
    }


}




WinForm.java

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

public class WinForm extends JFrame {
    //private String name;

    public WinForm(String title) throws HeadlessException {
        super(title);
        super.frameInit();
        //this.name = title;
        print();
    }
    public void print() {
        System.out.println(getTitle());
    }
}




Windows.java


import org.w3c.dom.Text;

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

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

        WinForm winForm = new WinForm("Window窗口");

        winForm.setSize(600, 400);
        winForm.setLocationRelativeTo(null);
        winForm.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        Picture picture = new Picture("LOGO图片","d:/background.jpg");
        picture.setBounds(200, 10, 160, 120);
        winForm.add(picture);

        Button loginButton = new Button("登录");
        loginButton.setBounds(200, 300, 80, 25);
        winForm.add(loginButton);

        Button registerButton = new Button("注册");
        registerButton.setBounds(300, 300, 80, 25);
        winForm.add(registerButton);

        Frame frame = new Frame("FRAME1");
        frame.setLayout(null);  //设置布局为 null
        winForm.add(frame);

        Lable userName = new Lable("用户名");
        userName.setBounds(100, 160, 80, 25);
        frame.add(userName);

        TextBox userNameBox = new TextBox("用户名文本框");
        userNameBox.setBounds(150, 160, 80, 25);
        frame.add(userNameBox);

        Lable passWord = new Lable("密码");
        passWord.setBounds(100, 210, 80, 25);
        frame.add(passWord);

        TextBox passWordBox = new TextBox("用户名文本框");
        passWordBox.setBounds(150, 210, 80, 25);
        frame.add(passWordBox);

        CheckBox rememberPwd = new CheckBox("记住户名");
        rememberPwd.setBounds(100, 250, 80, 25);
        //rememberPwd.setSize(,200);
        frame.add(rememberPwd);
/*
        Lable rememberPwdLabel = new Lable("记住用户名");
        rememberPwdLabel.setBounds(180, 250, 80, 25);
        frame.add(rememberPwdLabel);
*/
        Linkable retrievePwd = new Linkable("忘记密码");
        retrievePwd.setBounds(350, 250, 80, 25);
        frame.add(retrievePwd);

        winForm.setVisible(true);
    }

}




输出结果：





单例模式



实现类只创建一个实例。



私有构造函数： 使得外部无法通过new创建实例，

静态方法：能通过类获取类实例

私有静态变量：使得类实例化创建惟一对象。



  • 饿汉模式（推荐）

定义类时，单实例创建。

特点： 启动慢，引用快。



  • 懒汉模式

获取实例的时创建，需要synchronized同步等待，防止并发处理异常。

特点： 启动快，引用慢。





2020/10/11 更新



根据助教老师的建议又看了下 double-checked locking 方式实现的单例


public class Singleton {
  
    private Singleton() {}
    private volatile static Singleton instance = null;

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

}



对于 volatile， 查到网上帖子， 大多是是说由于编译器优化导致的指令重排可能导致new出来的对象的部分初始化问题， 我 查到的 比较早的资料 "Double-Checked Locking is Broken" Declaration

https://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html 提到 the Symantec JIT 会在构造函数前对申请对象的引用赋值。



最后一个解决方案来自Joshua Block的Effective Java（第3册），使用枚举.



public enum Singleton {
    INSTANCE;
    ...
}



2020-10-28 更新参考老师讲义写了个一个单例的工厂方法。



SingletonFactory.java

import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Properties;

public class SingletonFactory {
    private final static Properties IMPLS = loadImpls();


    private static Properties loadImpls() {
        Properties defaultImpls = new Properties();
        Properties impls = new Properties(defaultImpls);

        defaultImpls.setProperty("Singleton","Singleton");

        try{
            impls.load(SingletonFactory.class.getResourceAsStream("singleton.properties"));
        } catch (IOException e){
            throw new RuntimeException(e);
        }
        return impls;
    }
    @SuppressWarnings("unchecked")
    public  static <T> T getSingleton() {
        String implClassName = IMPLS.getProperty("Singleton");
        try {
            Class implClass = Class.forName(implClassName);
            Method m = implClass.getMethod("getInstance");
            return (T) m.invoke(null);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }
        return null;
    }
}




Singleton.java

public abstract class  Singleton {
    public  static Singleton getInstance(){
        return null;
    };
}




SingleNormal.java

public class SingletonNormal extends Singleton{
    private SingletonNormal(){System.out.println("Normal Singleton");};
    private static SingletonNormal instance = new SingletonNormal();
    public static Singleton getInstance(){
        return instance;
    }
}




SingleDoubleCheck.java

public class SingletonDoubleCheck extends Singleton{
    private SingletonDoubleCheck(){System.out.println("Double check Thread Safe Singleton");}
    private volatile static SingletonDoubleCheck instance = null;
    public static Singleton getInstance() {
        if (instance == null){
            synchronized (SingletonDoubleCheck.class){
                if (instance == null){
                    instance = new SingletonDoubleCheck();
                }
            }
        }
        return instance;
    }
}




SingletonLazy.java

public class SingletonLazy extends Singleton {
    private SingletonLazy() {System.out.println("Thread Safe Singleton");};
    private volatile static SingletonLazy instance = null;

    public static synchronized Singleton getInstance(){
        if (instance == null){
            instance = new SingletonLazy();
        }
        return instance;
    }
}




Client.java

public class Client {
    public static void main(String[] args){
        Singleton singleton1 = (Singleton) SingletonFactory.getSingleton();
        Singleton singleton2 = (Singleton) SingletonFactory.getSingleton();
        System.out.println(singleton1==singleton2);

    }
}


singleton.properties

Singleton=SingletonNormal



验证输出： 

Normal Singleton
true



可以通过修改配置文件 singleton.properties里 Singleton 指定不同的实现方式。



参考及引用



架构师训练营作业-李智慧老师相关讲义

Photo by Adrianna Calvo from Pexels



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发布于: 2020 年 10 月 04 日 阅读数: 45
架构师训练营第 1 期
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组合模式及单例模式