Kotlin program control

Kotlin Program control mind map

Catalog

if sentence

Branch judgment

Ternary expression

Block structure

for sentence

Incremental loop

Decreasing cycle

Combined with interval operator

Use with serialized objects

when sentence

Realization switch The function of

Realization if Select branch effect

And in or is Use a combination of

while sentence

do...while sentence

Jump statements

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if sentence

Branch judgment

    Kotlin Medium if One of the functions is Realization and Java in if Exactly the same Branch selection structure

    There are two commonly used forms if (condition) { } else { } 

                                  if (condition) { } else if(condition){ } else{ }

    var x:Int
    val num=50
    val input=Scanner(System.`in`)
    x=input.nextInt()
    if (x>num){
        println(" The input number is larger ")
    }else if (x<num){
        println(" The input number is small ")
    }else{
        println(" Input correct ")
    }

Ternary expression

  Java of use ? : To implement ternary expressions , But this grammar has not been JetBrains Accepted

  Kotlin It's using if ... else ... To realize the ternary expression

  grammar ：if (condition) value 1 else value 2

    var a:Int
    var b:Int
    val input=Scanner(System.`in`)
    a=input.nextInt()
    b=input.nextInt()
    println("$a"+" and "+"$b"+" The smaller one is : "+ if (a<b) a else b)

Block structure

  Kotlin in if It can also represent a multi branch block structure and return the value of the last statement in the corresponding block

    var a:Int
    var b:Int
    val input=Scanner(System.`in`)
    a=input.nextInt()
    b=input.nextInt()
    val x=if (a>b){
        println("$a > $b")
    }else if (a==b){
        println("$a = $b")
    }else{
        println("$a < $b")
    }
    println(x) // Output Unit, No return value 
    var x1=if (a>b){
        println("$a > $b")
        a-b
    }else if (a==b){
        println("$a = $b")
        0
    }else{
        println("$a < $b")
        b-a
    }
    println(x1) //Int A value of type 

for sentence

    Kotlin I've given up Java in for Of ( initial value ; Judge ; iteration ) Structure

Incremental loop

    Kotlin of use in and until Realized incremental cycle , You can use step Specify step size （ The default step size is 1）

    Kotlin The incremental loop implemented is [ a , b )

    var sum=0
    for (i in 1 until 9)
        sum+=i
    println(sum) // Realization 1~8 Sum of  36
    sum=0
    for (i in 1 until 10 step 2)
        sum+=i
    println(sum) //  Realization 1~9 Sum of odd numbers  25

Decreasing cycle

    Kotlin of use in and downTo The decreasing cycle is realized ,step The function of is consistent with the increasing cycle

    Kotlin The decreasing cycle realized is [ a , b ]

    var sum=0
    for (i in 9 downTo  1)
        sum+=i
    println(sum) // Realization 1~9 Sum of  45
    sum=0
    for (i in 8 downTo  0 step 2)
        sum+=i
    println(sum) //  Realization 0~8 Even sum of  20

Combined with interval operator

   in and Interval operator .. When used together, it can achieve similar until step by 1 The effect of , however The interval is double closed

    var sum=0
    for (i in 1..8)
        sum+=i
    println(sum) // 1~8 Sum up  36 
    //  use until Express   yes  1 until 9

Use with serialized objects

  in It can be used with serialized objects such as strings 、 Arrays combine , Directly implement the traversal of elements in the string and array

    var str="123456aurora"
    var arr= arrayOf(9,8,7,6,5)
    for (i in str)
        print("$i ") //1 2 3 4 5 6 a u r o r a
    println()
    for (i in arr)
        print("$i ")//9 8 7 6 5

when sentence

Realization switch The function of

  Kotlin of use when Instead of Java in switch The function of

  grammar when (condition) { case1->{ } case2->{ } case3,case4,case5->{ } else->{ }}

  The general use is shown in the uplink ：, amount to switch No break Of case, But it's a little different , stay Java in , these case Different blocks can be executed , but Kotlin The same block is executed in ;else amount to switch Medium defalut block

    var day:String
    val input=Scanner(System.`in`)
    day=input.next()
    when(day){
        "SunDay"->{
            println(" Today is Sunday ")
        }
        "MonDay"->{
            println(" Today is Monday ")
        }
        "TuesDay","SaturDay"->{
            println(" Today is Tuesday or Saturday ")
        }else->{
            println(" Today is Wednesday 、 Friday or Thursday ")
        }
    }

Realization if Select branch effect

   when It can also be realized if else Branch selection effect , It can also be nested if{ } else if{ } else{ } The selection effect of

    grammar ：when(condition){ true->{ } else->{ } }

              when(condition){ true->{ } else->{ when(condition){true->{} else->{ } } }

    var x:Int
    val num=50
    val input= Scanner(System.`in`)
    x=input.nextInt()
    when (x>num){
        true->{
            println("bigger")
        }
        else->{
            when(x==num){
                true->{
                    println("equal")
                }
                else->{
                    println("smaller")
                }
            }
        }
    }

And in or is Use a combination of

  And in or is Can also be used in combination with if Realization

  in It mainly determines whether the element is in the serialized object

  is It mainly determines whether the variable is of a certain type

    var arr= arrayOf(1,3,5,7,9)
    when(3){
        in arr->{
            println("is exit")
        }
        else->{
            println("no")
        }
    }
    if (3 in arr){
        println("is exit")
    }else{
        println("no")
    }
    when(arr){
        is Array<Int>->{ // Useless inspection 
            println("Yes")
        }else->{
            println("No")
        }
    }
    if (arr is Array<Int>){ // Useless inspection 
        println("Yes")
    }else{
        println("No")
    }

while sentence

  Kotlin in while Use of statements And Java Consistent with the use of

  while (condition) { }

do...while sentence

  Kotlin in do ... while Use of statements And Java Consistent with the use of

  do {   }while(condition)

Jump statements

    The jump statement has break ,continue ,return Three , Its use is also related to Java In the agreement

   break Indicates that subsequent statements will not be executed , Jump straight out of the loop

   continue Indicates that subsequent statements will not be executed , Execute next cycle

   return It is mainly used for the return value of functions , See blog for specific use Kotlin Basic functions