package com.study.dp.singleton; 
/** 
 * 传统方式实现单例模式 
 * @author CrazyPig 
 * 
 */ 
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(); 
  } 
}

package com.study.dp.singleton;  
/** 
 * 静态内部类实现单例模式 
 * @author CrazyPig 
 * 
 */ 
public class SpecialSingleton {    
  // 静态内部类 
  private static class NestClass { 
    private static SpecialSingleton instance; 
    static { 
      System.out.println("instance = new SingletonTest()"); 
      instance = new SpecialSingleton(); 
    } 
  }    
  // 不能直接new 
  private SpecialSingleton() { 
    System.out.println("private SingletonTest()"); 
  } 
  public static SpecialSingleton getInstance() { 
    System.out.println("SingletonTest getInstance()"); 
    return NestClass.instance; 
  } 
  public static void main(String[] args) { 
    SpecialSingleton instance = SpecialSingleton.getInstance(); 
    System.out.println("========================================"); 
    SpecialSingleton instance01 = SpecialSingleton.getInstance(); 
    System.out.println("========================================"); 
    SpecialSingleton instance02 = SpecialSingleton.getInstance(); 
  } 
}