常见的创建线程安全单例模式的方法

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/x4609883/article/details/79669960

1，同步代码块结合双检查锁机制实现单例

package com.thread;

public class Singleton {
	private static Singleton instance = null;

	/**
	 * 同步代码块结合双检查锁机制实现单例
	 * 
	 * @return
	 */
	public static Singleton getInstance() {
		try {
			if (instance == null) {
				synchronized (Singleton.class) {
					if (instance == null) {
						// 创建实例之前可能会有一些准备性的耗时工作
						Thread.sleep(300);
						instance = new Singleton();
					}
				}
			}
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		return instance;
	}
}

package com.thread;
public class Singleton {
	private static Singleton instance = null;

	/**
	 * 同步代码块结合双检查锁机制实现单例
	 * 
	 * @return
	 */
	public static Singleton getInstance() {
		try {
			if (instance == null) {
				synchronized (Singleton.class) {
					if (instance == null) {
						// 创建实例之前可能会有一些准备性的耗时工作
						Thread.sleep(300);
						instance = new Singleton();
					}
				}
			}
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		return instance;
	}
}

package com.thread;

public class Test_1 implements Runnable {

	@Override
	public void run() {
		System.out.println(Singleton.getInstance().hashCode());
	}

	public static void main(String[] args) {
		for(int i=0;i<10;i++) {
			Thread t = new Thread(new Test_1());
			t.start();
		}
	}

} 

测试结果，说明是同一个对象

2，同步方法实现单例

package com.thread;
public class Singleton_2 {
	private static Singleton_2 instance = null;

	/**
	 * 同步方法实现线程安全的单例
	 * 
	 * @return
	 */
	public static synchronized Singleton_2 getInstance() {
		try {
			if (instance == null) {
				Thread.sleep(300);
				instance = new Singleton_2();
			}
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		return instance;
	}
}

package com.thread;

public class Test_1 implements Runnable {

	@Override
	public void run() {
		System.out.println(Singleton_2.getInstance().hashCode());
	}

	public static void main(String[] args) {
		for(int i=0;i<10;i++) {
			Thread t = new Thread(new Test_1());
			t.start();
		}
	}

}

测试结果，线程安全

3，静态代码块

package com.thread;

public class Singleton_3 {
	private static Singleton_3 instance = null;
	static {
		instance = new Singleton_3();
	}
	
	public static Singleton_3 getInstance() {
		return instance;
	}
}

package com.thread;

public class Test_1 implements Runnable {

	@Override
	public void run() {
		System.out.println(Singleton_3.getInstance().hashCode());
	}

	public static void main(String[] args) {
		for(int i=0;i<10;i++) {
			Thread t = new Thread(new Test_1());
			t.start();
		}
	}

}

4，静态内部类

package com.thread;

public class Singleton_4 {
	private static class SingletonHandle{
		private static Singleton_4 instance = new Singleton_4();
	}
	
	public static Singleton_4 getInstance() {
		return SingletonHandle.instance;
	}
}

package com.thread;

public class Test_1 implements Runnable {

	@Override
	public void run() {
		System.out.println(Singleton_4.getInstance().hashCode());
	}

	public static void main(String[] args) {
		for(int i=0;i<10;i++) {
			Thread t = new Thread(new Test_1());
			t.start();
		}
	}

}

测试结果