Utilize Control Flow in Kotlin

May 22 2024 · Kotlin 1.9.23, Android 14, Kotlin Playground

Lesson 02: Leverage When Expressions

Demo

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    when {
      grade == 'A' -> println("Your grade is excellent")
      grade == 'B' -> println("You are very good")
      else -> {
        println("Your grade is lower than very good")
        println("Keep learning and improving!")
      }
    }

    when (grade) {
      'A' -> println("Your grade is excellent")
    }

    when (grade) {
      'A' -> println("Your grade is excellent")
      'B' -> println("You are very good")
      'C' -> println("Your grade is Good")
      'D' -> println("Your grade is Acceptable")
      'F' -> println("You failed")
    }

  else -> System.err.println("Unrecognized grade: $grade. Valid grades are A, B, C, D, and F.")

    when (val grade = args.firstOrNull()?.firstOrNull()) {
      'A' -> println("Your grade is excellent")
      'B' -> println("You are very good")
      'C' -> println("Your grade is Good")
      'D' -> println("Your grade is Acceptable")
      'F' -> println("You failed")
      else -> System.err.println("Unrecognized grade: $grade. Valid grades are A, B, C, D, and F.")
    }

    val result = when {
      grade == 'A' -> println("Your grade is excellent")
      grade == 'B' -> println("You are very good")
      else -> {
        println("Your grade is lower than very good")
        println("Keep learning and improving!")
      }
    }
    println(result)

    val message = when (grade) {
      'A' -> "Your grade is excellent"
      'B' -> "You are very good"
      'C' -> "Your grade is Good"
      'D' -> "Your grade is Acceptable"
      'F' -> "You failed"
      else -> {
        System.err.println("Unrecognized grade: $grade. Valid grades are A, B, C, D, and F.")
        "Your grade is unknown"
      }
    }
    println(message)

    val message = when (grade) {
      'A', 'B', 'C', 'D' -> "Your passed"
      'F' -> "You failed"
      else -> {
        System.err.println("Unrecognized grade: $grade. Valid grades are A, B, C, D, and F.")
        "Your grade is unknown"
      }
    }
    println(message)

    when {
      grade?.isLetter() == false -> System.err.println("Invalid grade: $grade")
      grade == 'A' -> println("Your grade is excellent")
    }

    val validGrades = setOf('A', 'B', 'C', 'D', 'F')
    when {
      grade in validGrades -> println("Your grade is valid")
    }

    val result = when {
      grade !in validGrades -> throw IllegalArgumentException("Invalid grade: $grade")
      grade == 'A' -> "Your grade is excellent"
      else -> "Your grade is valid"
    }
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