在多线程模式中，考虑到性能和线程安全问题，一般选择两种比较经典的单例模式，既能提高性能，也能保证线程安全 1、double check instance 双重检查锁定 原理参考链接：双重检查锁定原理链接
public class DubbleSingleton { private volatile 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(); } }2. static inner class 静态内部类模式
public class InnerSingleton { private static class Singletion { private static Singletion single = new Singletion(); } public static Singletion getInstance(){ return Singletion.single; } }