Kotlin Program Entry Point
An entry point of a Kotlin application is the main() function. A function can be defined as a block of code designed to perform a particular task.
Let”s start with a basic Kotlin program to print “Hello, World!” on the standard output:
fun main() { var string: String = "Hello, World!" println("$string") }
When you run the above Kotlin program, it will generate the following output:
Hello, World!
Entry Point with Parameters
Another form of main() function accepts a variable number of String arguments as follows:
fun main(args: Array<String>){ println("Hello, world!") }
When you run the above Kotlin program, it will generate the following output:
Hello, World!
If you have observed, its clear that both the programs generate same output, so it is very much optional to pass a parameter in main() function starting from Kotlin version 1.3.
print() vs println()
The print() is a function in Kotlin which prints its argument to the standard output, similar way the println() is another function which prints its argument on the standard output but it also adds a line break in the output.
Let”s try the following program to understand the difference between these two important functions:
fun main(args: Array<String>){ println("Hello,") println(" world!") print("Hello,") print(" world!") }
When you run the above Kotlin program, it will generate the following output:
Hello, world! Hello, world!
Both the functions (print() and println()) can be used to print numbers as well as strings and at the same time to perform any mathematical calculations as below:
fun main(args: Array<String>){ println( 200 ) println( "200" ) println( 2 + 2 ) print(4*3) }
When you run the above Kotlin program, it will generate the following output:
200 200 4 12
Semicolon (;) in Kotlin
Kotlin code statements do not require a semicolon (;) to end the statement like many other programming languages, such as Java, C++, C#, etc. do need it.
Though you can compile and run a Kotlin program with and without semicolon successfully as follows:
fun main() { println("I''m without semi-colon") println("I''m with semi-colon"); }
When you run the above Kotlin program, it will generate the following output:
I''m without semi-colon I''m with semi-colon
So as a good programming practice, it is not recommended to add a semicolon in the end of a Kotlin statement.
Packages in Kotlin
Kotlin code is usually defined in packages though package specification is optional. If you don”t specify a package in a source file, its content goes to the default package.
If we specify a package in Kotlin program then it is specified at the top of the file as follows:
package org.tutorialspoint.com fun main() { println("Hello, World!") }
When you run the above Kotlin program, it will generate the following output:
Hello, World!
Quiz Time (Interview & Exams Preparation)
Q 1 – Kotlin main() function should have a mandatory parameter to compile the code successfully:
Answer : B
Explanation
No it is not mandatory that Kotlin main() function should always have a parameter. If you need to pass multiple arguments through an array of string then you can use the paremeter like main(args: Array<String>), otherwise it is not required.
Q 2 – What will be the output of the following Kotlin program
fun main() { println("1"); println("2") }
Answer : C
Explanation
Though Kotlin does not recommend using a semicolon in the end of the statement, still if you want to separate two statements in a single line then you can separate them using a semicolon otherwise you will get compile time error.
Q 3 – Which of the following statement is correct in Kotlin
Answer : A
Explanation
Only A statement is correct here, because we can not run a Kotlin program without main() function, which is called an entry point for Kotlin program. It does not matter if you use print() or println() functions within a Kotlin program.
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