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在Scala中，提供了lazy值的特性，也就是说，如果将一个变量声明为lazy，则只有在第一次使用该变量时，变量对应的表达式才会发生计算。这种特性对于特别耗时的计算操作特别有用，比如打开文件进行IO，进行网络IO等。
scala> import scala.io.Source._
import scala.io.Source._
scala> lazy val lines = fromFile("C:\\Users\\Administrator\\Desktop\\test.txt").mkString
lines: String = <lazy>
scala> println(lines)
def sayHello(name:String,age:Int)={
if(age >18){
printf("Hi , %s , you are big boy !!!",name)
age
}else{
printf("Hi , %s , you are little boy !!!",name)
age
}
}
scala> lazy val lines = fromFile("C:\\Users\\Administrator\\Desktop\\test2222.txt").mkString
lines: String = <lazy>
scala> println(lines)
java.io.FileNotFoundException: C:\Users\Administrator\Desktop\test2222.txt (系统找不到指定的文件。)
at java.io.FileInputStream.open0(Native Method)
at java.io.FileInputStream.open(FileInputStream.java:195)
at java.io.FileInputStream.<init>(FileInputStream.java:138)
at scala.io.Source$.fromFile(Source.scala:91)
at scala.io.Source$.fromFile(Source.scala:76)
at scala.io.Source$.fromFile(Source.scala:54)
at .lines$lzycompute(<console>:16)
at .lines(<console>:16)
... 33 elided
scala> val lines = fromFile("C:\\Users\\Administrator\\Desktop\\test2222.txt").mkString
java.io.FileNotFoundException: C:\Users\Administrator\Desktop\test2222.txt (系统找不到指定的文件。)
at java.io.FileInputStream.open0(Native Method)
at java.io.FileInputStream.open(FileInputStream.java:195)
at java.io.FileInputStream.<init>(FileInputStream.java:138)
at scala.io.Source$.fromFile(Source.scala:91)
at scala.io.Source$.fromFile(Source.scala:76)
at scala.io.Source$.fromFile(Source.scala:54)
... 33 elided
scala>
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原文地址：http://www.cnblogs.com/thinkpad/p/5628465.html
