public class Singleton {
private static volatile Singleton singleton;
private Singleton() {
}
/**
* 分配内存空间
* 初始化内存空间
* 将引用指向内存空间
*
* 由于重排序,可能出现 1 -> 3 -> 2
* @return
*/
public static Singleton getSingleton() {
if (singleton == null) {
synchronized (Singleton.class) {
if (singleton == null) {
singleton = new Singleton();
}
}
}
return singleton;
}
public static void main(String[] args) {
for (int i = 0; i <= 50; i ++) {
new Thread(() -> {
System.out.println(Singleton.getSingleton());
}).start();
}
}
}