并发编程基础08-线程安全单例

版权声明：博观而约取，厚积而薄发。 https://blog.csdn.net/BruceLiu_code/article/details/88376169

  单例模式：最为常见的就是饿汉式和懒汉式。一个是直接实例化对象，一个是在调用的时候实例化对象。在多线程的模式中，往往要考虑到性能和线程安全的问题，我们一般选择两种比较经典的单例模式，在性能提高的同事，又能保证线程的安全。
静态内部类方式：

public class Singletion {
	
	private static class InnerSingletion {
		private static Singletion single = new Singletion();
	}
	
	public static Singletion getInstance(){
		return InnerSingletion.single;
	}
}

double check：

public class DubbleSingleton {

	private static DubbleSingleton ds;
	
	public  static DubbleSingleton getDs(){
		if(ds == null){
			try {
				//模拟初始化对象的准备时间...
				Thread.sleep(3000);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			synchronized (DubbleSingleton.class) {
				if(ds == null){
					ds = new DubbleSingleton();
				}
			}
		}
		return ds;
	}
	
	public static void main(String[] args) {
		Thread t1 = new Thread(new Runnable() {
			@Override
			public void run() {
				System.out.println(DubbleSingleton.getDs().hashCode());
			}
		},"t1");
		Thread t2 = new Thread(new Runnable() {
			@Override
			public void run() {
				System.out.println(DubbleSingleton.getDs().hashCode());
			}
		},"t2");
		Thread t3 = new Thread(new Runnable() {
			@Override
			public void run() {
				System.out.println(DubbleSingleton.getDs().hashCode());
			}
		},"t3");
		
		t1.start();
		t2.start();
		t3.start();
	}
	
}