学习路径：https://coding.imooc.com/learn/list/270.html 特点：该模式下的类十分饥渴，JVM装载类的时候就实例化对象。
public class HungrySingleton { private final static HungrySingleton hungrySingleton = new HungrySingleton(); private HungrySingleton(){} public static HungrySingleton getInstance() { return hungrySingleton; } } 单例实例在类加载时创建 – 线程安全 类加载、初始化相关 /** * 类初始化时就被实例化，虽然开始赋值为null, 实质还是使用类时即存在单例对象 */ public class HungrySingleton { // 静态成员变量 private final static HungrySingleton hungrySingleton = null; // 静态代码块， 静态成员和代码块按代码编写顺序执行，new逻辑要放到第二步 static { HungrySingleton = new HungrySingleton() } // 私有构造方法 private HungrySingleton(){} public static HungrySingleton getInstance() { return hungrySingleton; } }对比懒汉式
https://blog.csdn.net/chenghan_yang/article/details/90447741
