单例模式

java单例模式实现

package chapter02;

/*
 * 使用双检测机制，既保证了不需要同步代码的异步性，又保证了单例的效果
 */
public class MyObject {
    private volatile static MyObject myobject;
    
    private MyObject() {
        
    }
    
    public static MyObject getInstance() {
        
        try {
            if(myobject != null) {
                
            }else {
                Thread.sleep(3000);//模拟在生成对象之前的一些准备性工作
                synchronized (MyObject.class) {
                    if(myobject == null) {
                        myobject = new MyObject();
                    }
                }
            }
        } catch (InterruptedException e) {
            // TODO: handle exception
            e.printStackTrace();
        }
        
        return myobject;
    }
}

package chapter02;

public class MyThread extends Thread {

    @Override
    public void run() {
        // TODO Auto-generated method stub
        System.out.println(MyObject.getInstance().hashCode());
    }
}

package chapter02;

public class Run {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        MyThread t1 = new MyThread();
        MyThread t2 = new MyThread();
        t1.start();
        t2.start();
    }

}

使用静态内置类实现单例模式

package chapter03;

public class MyObject {
    //内部类实现
    private static class MyObjectHandler{
        private static MyObject myobejct = new MyObject();
    }
    
    public MyObject() {
        
    }
    
    public static MyObject getInstance() {
        return MyObjectHandler.myobejct;
    }
}

package chapter03;

public class MyThread extends Thread {

    @Override
    public void run() {
        // TODO Auto-generated method stub
        System.out.println(MyObject.getInstance().hashCode());
    }

    
}

package chapter03;


public class Run {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        MyThread t1 = new MyThread();
        MyThread t2 = new MyThread();
        t1.start();
        t2.start();
    }

}

使用static代码块实现单例模式

package chapter04;

public class MyObject {
    private static MyObject instance = null;
    
    private MyObject() {
        
    }
    
    static {
        instance = new MyObject();
    }
    
    public static MyObject getInstance() {
        return instance;
    }
    
}

package chapter04;

public class MyThread extends Thread {

    @Override
    public void run() {
        // TODO Auto-generated method stub
        for (int i = 0; i < 5; i++) {
            System.out.println(MyObject.getInstance().hashCode());
        }
    }
    
}

package chapter04;

public class Run {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        MyThread t1 = new MyThread();
        MyThread t2 = new MyThread();
        
        t1.start();
        t2.start();
    }

}

使用enum枚举数据类型实现单例模式

package chapter05;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class MyObject {
    public enum MyEnumSingleton{
        connectionFactory;
        private Connection connection;
        private MyEnumSingleton() {
            try {
                System.out.println("创建MyObject对象");
                String url = "jdbc:sqlserver://localhost:1079;databaseName=y2";
                String username = "sa";
                String password = "";
                String drivename = "com.microsoft.sqlserver.jdbc.SQLServerDriver";
                Class.forName(drivename);
                connection = DriverManager.getConnection(url, username, password);
                
                
            } catch (ClassNotFoundException e) {
                // TODO: handle exception
                e.printStackTrace();
            } catch (SQLException e) {
                // TODO: handle exception
                e.printStackTrace();
            }
        }
        
        public Connection getConnection() {
            return connection;
        }
    }
    
    public static Connection getConnection() {
        return MyEnumSingleton.connectionFactory.getConnection();
    }
}

package chapter05;

public class MyThread extends Thread {

    @Override
    public void run() {
        // TODO Auto-generated method stub
        for (int i = 0; i < 5; i++) {
            System.out.println(MyObject.getConnection().hashCode());
        }
    }
    
}