单例模式6种实现方式_写一个单例模式的例子,用代码实现

一：饿汉式

public class MyObject {
 
	// 立即加载方式==饿汉模式
	private static MyObject myObject = new MyObject();
 
	private MyObject() {
	}
 
	public static MyObject getInstance() {
		// 此代码版本为立即加载
		// 此版本代码的缺点是不能有其它实例变量
		// 因为getInstance()方法没有同步
		// 所以有可能出现非线程安全问题
		return myObject;
	}
}

public class MyThread extends Thread {
 
	@Override
	public void run() {
		System.out.println(MyObject.getInstance().hashCode());
	}
}

public static void main(String[] args) {
		MyThread t1 = new MyThread();
		MyThread t2 = new MyThread();
		MyThread t3 = new MyThread();
 
		t1.start();
		t2.start();
		t3.start();
 
	}

多线程获取单例，打印的hashcode是同一个值，说明对象是同一个 

二：懒汉式（1）

public class MyObject {
 
	private static MyObject myObject;
 
	private MyObject() {
	}
 
	// 设置同步方法效率太低了
	// 整个方法被上锁
	synchronized public static MyObject getInstance() {
		try {
			if (myObject != null) {
			} else {
				// 模拟在创建对象之前做一些准备性的工作
				Thread.sleep(3000);
				myObject = new MyObject();
			}
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		return myObject;
	}
 
}

public class MyThread extends Thread {
 
	@Override
	public void run() {
		System.out.println(MyObject.getInstance().hashCode());
	}
 
}

public static void main(String[] args) {
		MyThread t1 = new MyThread();
		MyThread t2 = new MyThread();
		MyThread t3 = new MyThread();
 
		t1.start();
		t2.start();
		t3.start();
 
	}

二：懒汉式（2）

public class MyThread extends Thread {
 
	@Override
	public void run() {
		System.out.println(MyObject.getInstance().hashCode());
	}
 
}

public class MyObject {
 
	private volatile static MyObject myObject;
 
	private MyObject() {
	}
 
	// 使用双检测机制来解决问题
	// 即保证了不需要同步代码的异步
	// 又保证了单例的效果
	public static MyObject getInstance() {
		try {
			if (myObject != null) {
			} else {
				// 模拟在创建对象之前做一些准备性的工作
				Thread.sleep(3000);
				synchronized (MyObject.class) {
					if (myObject == null) {
						myObject = new MyObject();
					}
				}
			}
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		return myObject;
	}
	// 此版本的代码称为：
	// 双重检查Double-Check Locking
 
}

public static void main(String[] args) {
		
		
		MyThread t1 = new MyThread();
		MyThread t2 = new MyThread();
		MyThread t3 = new MyThread();
 
		t1.start();
		t2.start();
		t3.start();
 
	}

三：使用静态内置类实现单例模式

public class MyObject {
 
	// 内部类方式
	private static class MyObjectHandler {
		private static MyObject myObject = new MyObject();
	}
 
	private MyObject() {
	}
 
	public static MyObject getInstance() {
		return MyObjectHandler.myObject;
	}
 
}

public class MyThread extends Thread {
 
	@Override
	public void run() {
		System.out.println(MyObject.getInstance().hashCode());
	}
 
}

public static void main(String[] args) {
		MyThread t1 = new MyThread();
		MyThread t2 = new MyThread();
		MyThread t3 = new MyThread();
 
		t1.start();
		t2.start();
		t3.start();
 
	}

四：使用静态代码块实现单例模式

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

public class MyThread extends Thread {
 
	@Override
	public void run() {
		for (int i = 0; i < 5; i++) {
			System.out.println(MyObject.getInstance().hashCode());
		}
	}
}

public static void main(String[] args) {
		MyThread t1 = new MyThread();
		MyThread t2 = new MyThread();
		MyThread t3 = new MyThread();
 
		t1.start();
		t2.start();
		t3.start();
 
	}

五：使用枚举实现单例模式

public enum MyObject {
	connectionFactory;
 
	private Connection connection;
 
	private MyObject() {
		try {
			System.out.println("调用了MyObject的构造");
			String url = "jdbc:sqlserver://localhost:1079;databaseName=ghydb";
			String username = "sa";
			String password = "";
			String driverName = "com.microsoft.sqlserver.jdbc.SQLServerDriver";
			Class.forName(driverName);
			connection = DriverManager.getConnection(url, username, password);
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		} catch (SQLException e) {
			e.printStackTrace();
		}
	}
 
	public Connection getConnection() {
		return connection;
	}
}

public class MyThread extends Thread {
 
	@Override
	public void run() {
		for (int i = 0; i < 5; i++) {
			System.out.println(MyObject.connectionFactory.getConnection()
					.hashCode());
		}
	}
}

public static void main(String[] args) {
		MyThread t1 = new MyThread();
		MyThread t2 = new MyThread();
		MyThread t3 = new MyThread();
 
		t1.start();
		t2.start();
		t3.start();
 
	}

六：序列化与反序列化的单例模式实现

public class MyObject implements Serializable {
 
	private static final long serialVersionUID = 888L;
 
	// 内部类方式
	private static class MyObjectHandler {
		private static final MyObject myObject = new MyObject();
	}
 
	private MyObject() {
	}
 
	public static MyObject getInstance() {
		return MyObjectHandler.myObject;
	}
 
	protected Object readResolve() throws ObjectStreamException {
		System.out.println("调用了readResolve方法！");
		return MyObjectHandler.myObject;
	}
 
}

public class SaveAndRead {
 
	public static void main(String[] args) {
		try {
			MyObject myObject = MyObject.getInstance();
			
			FileOutputStream fosRef = new FileOutputStream(new File(
					"myObjectFile.txt"));
			ObjectOutputStream oosRef = new ObjectOutputStream(fosRef);
			oosRef.writeObject(myObject);
			oosRef.close();
			fosRef.close();
			System.out.println(myObject.hashCode());
		} catch (FileNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
 
		try {
			FileInputStream fisRef = new FileInputStream(new File(
					"myObjectFile.txt"));
			ObjectInputStream iosRef = new ObjectInputStream(fisRef);
			MyObject myObject = (MyObject) iosRef.readObject();
			iosRef.close();
			fisRef.close();
			System.out.println(myObject.hashCode());
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		}
 
	}
 
}