Scala 类中的 val 和 object? [英] val and object inside a scala class?
本文介绍了Scala 类中的 val 和 object?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
在 scala 类中将字段声明为 val
、lazy val
和 object
有什么区别,如下面的代码片段所示:
What is the difference between declaring a field as val
, lazy val
and object
inside a scala class, as in the following snippet:
class A
class B {
val a1 = new A { def foo = 1 }
object a2 extends A { def foo = 1 }
lazy val a3 = new A { def foo = 1 }
}
推荐答案
在前者中,任何包含的代码都会在创建类 B 后立即执行.然而,在后者中,在您实际使用该对象之前,它不会被实例化.
In the former, any code included is executed as soon as class B is created. In the latter, however, until you actually use the object, it won't be instantiated.
您可以在这里看到不同之处:
You can see the difference here:
class A { println("Creating a new A") }
class B {
val a1 = new A { println("a1"); def foo = 1 }
object a2 extends A { println("a2"); def foo = 1 }
}
scala> val b = new B
Creating a new A
a1
b: B = B@1176e8a
scala> b.a2.foo
Creating a new A
a2
res0: Int = 1
在创建的 .class 文件的名称等方面也存在隐藏的差异;当然,两者有不同的类型.
There are also hidden differences in what the created .class files are named and such; and of course the two have different types.
这篇关于Scala 类中的 val 和 object?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!
查看全文