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Scala | Trait App
  • Last Updated : 12 Apr, 2019

App is a trait which is utilized to rapidly change objects into feasible programs, which is carried out by applying DelayedInit function and the objects inheriting the trait App uses this function to execute the entire body of the program as a section of an inherited main method.
Note:

trait App extends DelayedInit
  • The Linear Super-types here are:
    DelayedInit, AnyRef, Any
  • The value members are:
    val executionStart: Long
    def main(args: Array[String]): Unit

    Now, lets see some examples.

    • Example :




      // Scala program of a trait
      // App
        
      // Applying the trait App
      object GfG extends App
      {
        
          // Displays output
          println("GeeksforGeeks")
        
      }
      Output:
      GeeksforGeeks
      

      Here, the object GfG inherits the main method of App and prints the output, and so we don’t need to create the main method manually.

    • Example:




      // Scala program of trait
      // App
      object GfG extends App 
      {
          // conditions stated
          if (args.length == 1)
          {
        
              // Displays this as output if 
              // the command line arguments
              // are equal to one
              println("Student: ${args(0)}")
          }
            
          else
          {
            
              // Displays this if no arguments 
              // are given in the command line
              println("There are no students.")
          }
      }
      Output:
      There are no students.
      

      Note: Here, args is utilized for command line arguments, which will return the instant command line arguments like an array.
      The output obtained here is the string stated above in the else part as no command line arguments are provided. If we provide the command line arguments like below then the output will be:

      // command line argument
      $ scala GfG Nidhi 
      
      // Output
      Student: Nidhi
      

      Here, one argument is given so only that is returned.




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