unable to print multiple Boolean in Kotlin

Question

i'm beginning with kotlin language

fun main (args:Array<String>){


    var flag1:Boolean= true //Explicit declaration
    var flag2: =false //Implicit declaration

     println(flag2 + "and " + flag1)

     println(flag1)
     println(flag2)

}

in above code i have declared 2 type of boolean Explicit and Implicit declaration

for above code i would say expect following ouput :-

false and true 

true

false

but i'm getting following erroe :-

can anyone explain where did i go wrong ?

I'm pretty sure you must stringify your booleans explicitly. This is not PHP, you know :) — Sergio Tulentsev, Dec 25 '17 at 14:25
What the error message tells you, is kotlin failed to find such overload of operator `+` where left part is a boolean and right is a string. — Sergio Tulentsev, Dec 25 '17 at 14:26
also `var flag2: =false` is invalid code, this won't even compile. — Sergio Tulentsev, Dec 25 '17 at 14:28
In addition to the comments above, you should use string interpolation, not concatenation. — Sulthan, Dec 25 '17 at 14:28

Marko Devcic · Accepted Answer · 2017-12-25T14:46:12.360

For that compiler error, change this:

println(flag2 + "and " + flag1)

to this:

println("$flag2 and $flag1")

Kotlin is strongly typed language and you can't use plus operator on String and Boolean types.

But you can use string interpolation, with $ operator inside a string literal.

You could also make it compile with overloaded plus operator on the Boolean type by adding this:

operator fun Boolean.plus(s: String): String {
    return this.toString() + s
}

score 3 · Answer 2 · answered Dec 25 '17 at 14:43

In Java, it performs string conversion when you concatenate a string with any type of object. For example,

System.out.println(true + " and false");    //Output: true and false

In Kotlin, string conversion doesn't exist. Alternatively, you may use string templates for that.

println("$flag2 and $flag1")

Besides, since Kotlin's String class provide plus(Any?) function which receives any type as parameter, so the following line of code is still valid:

println("$flag2 and " + flag1)

Here is a discussion on this design.

Or `println("" + flag2 + " and " + flag1)` – voddan Dec 25 '17 at 15:25 — voddan, Dec 25 '17 at 15:25

unable to print multiple Boolean in Kotlin

2 Answers2