包对象何时初始化? [英] When are package objects initialized?

问题描述

如果我定义了包对象

package com.something.else

package object more {
    val time = System.currentTimeMillis
    // ... other stuff ...
}

，然后将其导入源代码中的某个位置.

which is then imported somewhere in the source code.

import com.something.else.more

此对象(及其成员)何时初始化/构造?

When is this object (and its members) initialized/constructed?

换句话说，什么决定了more.time的值?
程序首次启动时是否进行评估?还是第一次访问它?还是第一次访问more?

In other words, what determines the value of more.time?
Is it evaluated when the program first starts? Or the first time it is accessed? Or the first time more is accessed?

推荐答案

很容易检查:

package something

package object more {
  val time = System.currentTimeMillis
}

// in separate file:
package something.more

object Test extends App {
  val now = System.currentTimeMillis

  Thread.sleep(1000)

  println(now)
  println(time)
}

给予:

1339394348495
1339394349496

第二次是大约1000毫秒之后，所以这是第一次访问包对象，就像处理其他任何对象一样.

The second time is ~1000 ms later, so it's when the package object is first accessed, as it would be with any other object.

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