方式1（推荐）
package singleton; public class Singletion { private static class InnerSingletion { private static Singletion single = new Singletion(); } public static Singletion getInstance(){ return InnerSingletion.single; } }方式2（double check）
package singleton; 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(); } }