Java中静态内部类怎么利用单例模式实现

package com.study.dp.singleton;  public class TraditionalSingletion {   // 单实例   private static TraditionalSingletion instance;      // 不让new   private TraditionalSingletion() {     System.out.println("private TraditionalSingletion()");   }      public synchronized static TraditionalSingletion getInstance() {     System.out.println("TraditionalSingletion getInstance()");     if(instance == null) {       System.out.println("instance = new TraditionalSingletion()");       instance = new TraditionalSingletion();     }     return instance;   }      public static void main(String[] args) {     TraditionalSingletion instance = TraditionalSingletion.getInstance();     System.out.println("========================================");     TraditionalSingletion instance01 = TraditionalSingletion.getInstance();     System.out.println("========================================");     TraditionalSingletion instance02 = TraditionalSingletion.getInstance();   } }