本文参考IcyFenix在javaeye的博客http://icyfenix.javaeye.com/blog/575052讲述的内容
向IcyFenix致敬！
// 1、饿汉式
/**
* 饿汉式单例
*
* @author Lrwin
*
*/
public class HungrySingleton {
/** jvm保证instance只被初始化一次 */
private static HungrySingleton instance = new HungrySingleton();
/** 阻止外部使用new实例化对象 */
private HungrySingleton() {
}
/**
* 获取实例
*
* @return 唯一的instance
*/
public static HungrySingleton getInstance() {
return instance;
}
}
// 2、懒汉式
/**
* 懒汉式单例
*
* @author Lrwin
*
*/
public class LazySingleton {
/**
* 阻止外界使用new实例化对象
*/
private LazySingleton() {
}
/**
* 只有在调用getInstance()时此类才会被装载 在SingletonKerriganF.java中说明了加载顺序
*/
private static class SingletonHolder {
/**
* 对象实例,jvm保证只初始化一次
*/
static final LazySingleton INSTANCE = new LazySingleton();
}
/**
* 获取实例
*
* @return 返回唯一实例
*/
public LazySingleton getInstance() {
return SingletonHolder.INSTANCE;
}
}
// 3、懒汉式单例内部类加载顺序 （来自http://www.javaeye.com/topic/575052）
/**
* 实现单例访问Kerrigan的第六次尝试
*
* @author IcyFenix
* @see http://www.javaeye.com/topic/575052
*/
public class SingletonKerriganF {
private static String arg = null;
private static class SingletonHolder {
/**
* 单例对象实例
*/
static final SingletonKerriganF INSTANCE = new SingletonKerriganF();
}
public static SingletonKerriganF getInstance() {
return SingletonHolder.INSTANCE;
}
public SingletonKerriganF() {
System.out.println("Kerrigan get arg:" + getArg());
System.out.println("Kerrigan created!");
}
public static String getArg() {
return arg;
}
public static void setArg(String arg) {
SingletonKerriganF.arg = arg;
}
public static void main(String[] args) {
System.out
.println("SingletonKerriganF was loaded,but SingletonKerriganF$SingletonHolder don't");
SingletonKerriganF.setArg("this maybe some config files etc....");
SingletonKerriganF.getInstance();
}
}