Scala Programming Projects

lazy val

When we use the lazy prefix in front of val or var (as shown in the following code), it is evaluated only when needed:

class LazyDemo {
  lazy val lazyVal = {
    println("Evaluating lazyVal")
    "Hello"
  }
}
val lazyDemo = new LazyDemo
//lazyDemo: LazyDemo = LazyDemo@13ca84d5

When we instantiate the class, the block at the right side of the assignment is not evaluated. It will only get evaluated when we use the variable, as shown in the following code:

lazyDemo.lazyVal + " World"
//Evaluating lazyVal
//res0: String = Hello World

This mechanism allows you to defer the evaluation of computationally expensive operations. For instance, you could use it to start an application quickly and run the initialization code only when the first user ...