Scala中的"null" 和“_”来初始化对象

Alternatives

Use null as a last resort. As already mentioned, Option replaces most usages of null. If you using null to implement deferred initialisation of a field with some expensive calculation, you should use a lazy val.

Canonical initialisation to null

That said, Scala does support null. I personally use it in combination with Spring Dependency Injection.

Your code is perfectly valid. However, I suggest that you use var t: T = _ to initialize t to it's default value. If T is a primitive, you get the default specific to the type. Otherwise you get null.

Not only is this more concise, but it is necessary when you don't know in advance what T will be:

scala> class A[T] { var t: T = _ }

defined class A

scala> new A[String].t

res0: String = null

scala> new A[Object].t

res1: java.lang.Object = null

scala> new A[Int].t

res2: Int = 0

scala> new A[Byte].t

res3: Byte = 0

scala> new A[Boolean].t

res4: Boolean = false

scala> new A[Any].t

res5: Any = null

Advanced

Using var t: T= null is a compile error if T is unbounded:

scala> class A[T] { var t: T = null }

<console>:5: error: type mismatch;

 found   : Null(null)

 required: T

       class A[T] { var t: T = null }

You can add an implicit parameter as evidence that T is nullable -- a subtype of AnyRef not a subtype of NotNull This isn't fully baked, even in Scala 2.8, so just consider it a curiousity for now.

scala> class A[T](implicit ev: Null <:< T) { var t: T = null }

defined class A

参考链接：

https://stackoverflow.com/questions/2440134/is-this-the-proper-way-to-initialize-null-references-in-scala

巴特西

Scala中的"null" 和“_”来初始化对象

Alternatives

Canonical initialisation to null

Advanced

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