试图了解Kotlin示例(Trying to understand Kotlin Example)

 我想学习Kotlin，并通过try.kotlinlang.org上的示例进行工作 
 
 我无法理解一些示例，特别是Lazy属性示例： https : //try.kotlinlang.org/#/Examples/Delegated%20properties/Lazy%20property/Lazy%20property.kt 
 
/**
 * Delegates.lazy() is a function that returns a delegate that implements a lazy property:
 * the first call to get() executes the lambda expression passed to lazy() as an argument
 * and remembers the result, subsequent calls to get() simply return the remembered result.
 * If you want thread safety, use blockingLazy() instead: it guarantees that the values will
 * be computed only in one thread, and that all threads will see the same value.
 */

class LazySample {
    val lazy: String by lazy {
        println("computed!")
        "my lazy"
    }
}

fun main(args: Array<String>) {
    val sample = LazySample()
    println("lazy = ${sample.lazy}")
    println("lazy = ${sample.lazy}")
}
 
 输出： 
 
computed!
lazy = my lazy
lazy = my lazy
 
 我不知道这里发生了什么。 （可能是因为我不熟悉lambda） 
 
 
 
 为什么println（）只执行一次？ 
 
 
 我也对“我懒”字符串没有分配给任何东西（String x =“my lazy”）或返回中使用（返回“我的懒惰”）这一行感到困惑。 
 
 
 有人可以解释吗？ :) 

I want to learn Kotlin and am working through the Examples on try.kotlinlang.org
 
I have trouble understanding some examples, particularly the Lazy property example: https://try.kotlinlang.org/#/Examples/Delegated%20properties/Lazy%20property/Lazy%20property.kt
 
/**
 * Delegates.lazy() is a function that returns a delegate that implements a lazy property:
 * the first call to get() executes the lambda expression passed to lazy() as an argument
 * and remembers the result, subsequent calls to get() simply return the remembered result.
 * If you want thread safety, use blockingLazy() instead: it guarantees that the values will
 * be computed only in one thread, and that all threads will see the same value.
 */

class LazySample {
    val lazy: String by lazy {
        println("computed!")
        "my lazy"
    }
}

fun main(args: Array<String>) {
    val sample = LazySample()
    println("lazy = ${sample.lazy}")
    println("lazy = ${sample.lazy}")
}
 
Output:
 
computed!
lazy = my lazy
lazy = my lazy
 
I don't get what is happening here. (probably because I am not really familiar with lambdas)
 
 
 
Why is the println() only executed once?
 
 
I am also confused about the line "my lazy" the String isn't assigned to anything (String x = "my lazy") or used in a return (return "my lazy)
 
 
Can someone explain please? :)

原文：https://stackoverflow.com/questions/46573364