Singleton mode, to ensure that a class has only one instance, and to provide a global access point to access it
The hungry Chinese singleton instantiates an object and gives it a reference when the singleton class is loaded;
The lazy singleton will only instantiate an object and give it its own reference only when it is actually used.
/*
*饿汉式单例
*我们知道，类加载的方式是按需加载，且加载一次。因此，在上述单例类被加载时，
*就会实例化一个对象并交给自己的引用，供系统使用；而且，由于这个类在整个
*生命周期中只会被加载一次，因此只会创建一个实例，即能够充分保证单例
*/
public class Singleton1 {
private static Singleton1 singleton1 = new Singleton1();//创建自己的静态对象
private Singleton1(){
private构造方法，堵死了外界利用new创建此类实例的可能
}
// 以自己实例为返回值的静态的公有方法
public static Singleton1 getSingleton1(){
return singleton1;
}
}
/*
*懒汉式单例单例实例被延迟加载，即只有在真正使用的时候才会实例化
*一个对象并交给自己的引用
*/
public class Singleton2 {
private static Singleton2 singleton2;
private Singleton2(){
}
// 以自己实例为返回值的静态的公有方法，静态工厂方法
public synchronized static Singleton2 getSingleton2(){
// 被动创建，在真正需要使用时才去创建
if (singleton2 == null) {
singleton2 = new Singleton2();
}
return singleton2;
}
}
From the perspective of speed and response time, the hungry style (also known as immediate loading) is better; in terms of resource utilization efficiency, the lazy style (also known as lazy loading) is better.