1、使用内部类，而且它是线程安全的，而且只创建一次：
/**
Prof Bill Pugh, University of Maryland, was the main force behind java memory
model changes. His principle Initialization-on-demand holder idiom also uses
static block but in different way. It suggest to use static inner class.
*/
public class Singleton {
/**
* Returns Singleton instance
* @return Singleton
*/
public static Singleton getInstance() {
return InstanceHolder.INSTANCE;
}
// private constructor prevents instantiation from other classes
private Singleton () {
}
// Maintains single instance of class
private static class InstanceHolder {
private static final Singleton INSTANCE = new Singleton();
}
}
Read more: http://javarevisited.blogspot.com/2014/05/double-checked-locking-on-singleton-in-java.html#ixzz3uvGIuYWT
2、使用enum，因为它是线程安全的，而且只创建一次
/**
* 枚举单例
* @author Administrator
*
*/
public enum EnumSingleton {
INSTANCE;
/**
* 私有构造方法
*/
private EnumSingleton(){
System.out.println("-----构造方法");
}
/**
* 实现函数
* @param i
*/
public void say(int i){
System.out.println("i :" + i);
}
/**
* 测试
* @param args
*/
public static void main(String[] args) {
EnumSingleton.INSTANCE.say(1);
EnumSingleton.INSTANCE.say(2);
EnumSingleton.INSTANCE.say(3);
}
}