Use of Boolean? in if expression

Question

If I have a nullable Boolean b, I can do the following comparison in Java:

Boolean b = ...;
if (b != null && b) {
   /* Do something */
         


        

Answer 1

In case if you want to perform operations alike contain on a String you could use equality check like below -

if (url?.contains("xxx") == true){
  return false;
}

Answer 2

If you want to cleanly check whether a Boolean? is true or false you can do:

when(b) {
    true -> {}
    false -> {}
}

If you want to check if it's null you can add that (or else) as a value in the when:

when(b) {
    true -> {}
    false -> {}
    null -> {}
}

when(b) {
    true -> {}
    false -> {}
    else-> {}
}

Answer 3

In Kotlin, you can do like this:

val b: Boolean? = true
if (b == true) { // if b is null, this should be null == true
    /* Do something */
} else {
    /* Do something else */
}

Answer 4

You can do with safe Operator "let"

val b: Boolean? = null
b?.let { flag ->
    if(flag){
        // true Block
    } else {
        // false Block
    }
}

Answer 5

Kotlin will statically analyze your null checks. This is fine:

val b: Boolean? = null
if (b != null && b) {
    println(b)
}

Even though this fails with type error:

val b: Boolean? = null
if (b == null && b) {
    println(b)
}

For more see: http://kotlinlang.org/docs/reference/null-safety.html

You can also use "null coalescing operator" (which will work for mutable variables):

val b: Boolean? = null
if (b ?: false) {
    println(b)
}

Answer 6

You can compare nullable boolean with true, false or null using equality operator:

var b: Boolean? = null
if (b == true) {
    // b was not null and equal true
} 
if (b == false) {
   // b is false 
}
if (b != true) { 
   // b is null or false 
}