test 是匿名对象 AbstractTest 的具体子类（请注意，它实现了 AbstractTest 的所有抽象方法），这就是为什么该子类

test is an object of an anonymous concrete sub-class of AbstractTest (note that it implements all the abstract methods of AbstractTest), which is why this sub-class can be instantiated.

另一方面，

AbstractTest test = new AbstractTest();

不会通过编译，因为那是实例化抽象类的尝试。

wouldn't pass compilation, since that would be an attempt to instantiate an abstract class.