Basic examples

The Unit return type declaration is optional for functions. The following codes are equivalent.

fun printHello(name: String?): Unit {
    if (name != null)
        println("Hello ${name}")
}

fun printHello(name: String?) {
    ...
}

Single-Expression functions:When a function returns a single expression, the curly braces can be omitted and the body is specified after = symbol

fun double(x: Int): Int = x * 2

Explicitly declaring the return type is optional when this can be inferred by the compiler

fun double(x: Int) = x * 2

String interpolation: Using string values is easy.

In java:
    int num=10
    String s  = "i =" + i;

In Kotlin
    val num = 10
    val s = "i = $num"

In Kotlin, the type system distinguishes between references that can hold null (nullable references) and those that can not (non-null references). For example, a regular variable of type String can not hold null:

var a: String = "abc"
a = null // compilation error

To allow nulls, we can declare a variable as nullable string, written String?:

var b: String? = "abc"
b = null // ok

In Kotlin,== actually checks for equality of values.By convention, an expression like a == b is translated to

a?.equals(b) ?: (b === null)