val和对象在一个scala类中？ [英] val and object inside a scala class?

问题描述

声明一个字段为 val ， lazy val 和对象在一个scala类中，如下面的代码片段所示：

  class A 
 
 class B {
 val a1 = new A {def foo = 1} 
对象a2 extends A {def foo = 1} 
 lazy val a3 = new A {def foo = 1} 
} 
  

解决方案

包括在创建B类时立即执行。然而，在后者中，直到你实际使用对象，它不会被实例化。

你可以看到区别：

class A {println（Creating a new A）}
class B {
val a1 = new A {println ）; def foo = 1}
对象a2 extends A {println（a2）; def foo = 1}
}

scala> val b = new B
创建一个新的A
a1
b：B = B @ 1176e8a

scala> b.a2.foo
创建新的A
a2
res0：Int = 1


b $ b

在创建的.class文件被命名等方面也有隐藏的差异;当然两者有不同的类型。

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 }
}

解决方案

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.

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

There are also hidden differences in what the created .class files are named and such; and of course the two have different types.

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