1 饿汉式单例类.在类初始化时，已经自行实例化
class EagerSingleton {
private static final EagerSingleton m_instance = new EagerSingleton();
/** * 私有的默认构造子 */
private EagerSingleton() {
}
/**
* * 静态工厂方法
*/
public static EagerSingleton getInstance() {
return m_instance;
}
}
