只有一个构造函数.默认值保留在人"随行对象中.呼叫 new Person(年龄= 10)会变成类似 new Person(Person.< init> $ default $ 1()，10).

There is only one constructor. The default values are kept in the Person companion object. A call new Person(age = 10) is turned into something like new Person(Person.<init>$default$1(), 10).