Android question mark after variable [duplicate]

-2

This question already has an answer here:

In Kotlin, what is the idiomatic way to deal with nullable values, referencing or converting them

2 answers

I sometimes see statements like somevariable.value?.add() What purpose does the question mark serve?
(Sorry, at the time of post I had no idea this was Kotlin, I thought it was java)

edited Nov 29 '18 at 20:57

asked Nov 23 '18 at 21:31

lostScriptie

457

marked as duplicate by Jayson Minard kotlin
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Nov 25 '18 at 14:36

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

1

This is not Java code. It's Kotlin.

– forpas
Nov 23 '18 at 21:34

kotlinlang.org/docs/reference/null-safety.html

– Zoe
Nov 24 '18 at 8:36

You said in another comment " I haven't delved into Kotlin yet even though I know I should be so" ... Therefore you asked this question before you took the time to look it up. Please do the opposite and try to resolve things on your own with reasonable effort before asking.

– Jayson Minard
Nov 25 '18 at 14:33

add a comment |

-2

This question already has an answer here:

In Kotlin, what is the idiomatic way to deal with nullable values, referencing or converting them

2 answers

I sometimes see statements like somevariable.value?.add() What purpose does the question mark serve?
(Sorry, at the time of post I had no idea this was Kotlin, I thought it was java)

edited Nov 29 '18 at 20:57

asked Nov 23 '18 at 21:31

lostScriptie

457

marked as duplicate by Jayson Minard kotlin
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Nov 25 '18 at 14:36

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

1

This is not Java code. It's Kotlin.

– forpas
Nov 23 '18 at 21:34

kotlinlang.org/docs/reference/null-safety.html

– Zoe
Nov 24 '18 at 8:36

You said in another comment " I haven't delved into Kotlin yet even though I know I should be so" ... Therefore you asked this question before you took the time to look it up. Please do the opposite and try to resolve things on your own with reasonable effort before asking.

– Jayson Minard
Nov 25 '18 at 14:33

add a comment |

-2

This question already has an answer here:

In Kotlin, what is the idiomatic way to deal with nullable values, referencing or converting them

2 answers

I sometimes see statements like somevariable.value?.add() What purpose does the question mark serve?
(Sorry, at the time of post I had no idea this was Kotlin, I thought it was java)

edited Nov 29 '18 at 20:57

asked Nov 23 '18 at 21:31

lostScriptie

457

This question already has an answer here:

In Kotlin, what is the idiomatic way to deal with nullable values, referencing or converting them

2 answers

I sometimes see statements like somevariable.value?.add() What purpose does the question mark serve?
(Sorry, at the time of post I had no idea this was Kotlin, I thought it was java)

This question already has an answer here:

In Kotlin, what is the idiomatic way to deal with nullable values, referencing or converting them

2 answers

kotlin

edited Nov 29 '18 at 20:57

asked Nov 23 '18 at 21:31

lostScriptie

457

edited Nov 29 '18 at 20:57

asked Nov 23 '18 at 21:31

lostScriptie

457

edited Nov 29 '18 at 20:57

asked Nov 23 '18 at 21:31

lostScriptie

457

asked Nov 23 '18 at 21:31

lostScriptie

457

asked Nov 23 '18 at 21:31

lostScriptie

457

marked as duplicate by Jayson Minard kotlin
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Nov 25 '18 at 14:36

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Nov 25 '18 at 14:36

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

1

This is not Java code. It's Kotlin.

– forpas
Nov 23 '18 at 21:34

kotlinlang.org/docs/reference/null-safety.html

– Zoe
Nov 24 '18 at 8:36

You said in another comment " I haven't delved into Kotlin yet even though I know I should be so" ... Therefore you asked this question before you took the time to look it up. Please do the opposite and try to resolve things on your own with reasonable effort before asking.

– Jayson Minard
Nov 25 '18 at 14:33

add a comment |

1

This is not Java code. It's Kotlin.

– forpas
Nov 23 '18 at 21:34

kotlinlang.org/docs/reference/null-safety.html

– Zoe
Nov 24 '18 at 8:36

You said in another comment " I haven't delved into Kotlin yet even though I know I should be so" ... Therefore you asked this question before you took the time to look it up. Please do the opposite and try to resolve things on your own with reasonable effort before asking.

– Jayson Minard
Nov 25 '18 at 14:33

This is not Java code. It's Kotlin.

– forpas
Nov 23 '18 at 21:34

kotlinlang.org/docs/reference/null-safety.html

– Zoe
Nov 24 '18 at 8:36

You said in another comment " I haven't delved into Kotlin yet even though I know I should be so" ... Therefore you asked this question before you took the time to look it up. Please do the opposite and try to resolve things on your own with reasonable effort before asking.

– Jayson Minard
Nov 25 '18 at 14:33

add a comment |

1 Answer
1

active

oldest

votes

Kotlin treats null as something more than the source of null-pointer exceptions.

In your code snippet, somevariable.value is of a "nullable type", such as MutableList? or Axolotl?. A MutableList cannot be null, but a MutableList? might be null.

Normally, to call a function on an object, you use a ..

One option for calling a function on a variable, parameter, or property that is
of a nullable type is to use ?.. Then, one of two things will happen:

If the value is null, your function call is ignored, and null is the
result

If the value is not null, your function call is made as normal

So, in your case:

If somevariable.value is null, the add() call is skipped

If somevariable.value is not null, the add() call is made on whatever somevariable.value is

answered Nov 23 '18 at 21:45

CommonsWare

773k13918891936

one possibly should also take !! for @NonNull into account.

– Martin Zeitler
Nov 23 '18 at 22:32

there is a book, already: kotlinlang.org/docs/reference/null-safety.html

– Martin Zeitler
Nov 23 '18 at 22:38

Thank you - I haven't delved into Kotlin yet even though I know I should be so this check threw me off. I can clearly see the value of Kotlin.

– lostScriptie
Nov 24 '18 at 17:07

add a comment |

1 Answer
1

active

oldest

votes

1 Answer
1

active

oldest

votes

Kotlin treats null as something more than the source of null-pointer exceptions.

In your code snippet, somevariable.value is of a "nullable type", such as MutableList? or Axolotl?. A MutableList cannot be null, but a MutableList? might be null.

Normally, to call a function on an object, you use a ..

One option for calling a function on a variable, parameter, or property that is
of a nullable type is to use ?.. Then, one of two things will happen:

If the value is null, your function call is ignored, and null is the
result

If the value is not null, your function call is made as normal

So, in your case:

If somevariable.value is null, the add() call is skipped

If somevariable.value is not null, the add() call is made on whatever somevariable.value is

answered Nov 23 '18 at 21:45

CommonsWare

773k13918891936

one possibly should also take !! for @NonNull into account.

– Martin Zeitler
Nov 23 '18 at 22:32

there is a book, already: kotlinlang.org/docs/reference/null-safety.html

– Martin Zeitler
Nov 23 '18 at 22:38

Thank you - I haven't delved into Kotlin yet even though I know I should be so this check threw me off. I can clearly see the value of Kotlin.

– lostScriptie
Nov 24 '18 at 17:07

add a comment |

Kotlin treats null as something more than the source of null-pointer exceptions.

In your code snippet, somevariable.value is of a "nullable type", such as MutableList? or Axolotl?. A MutableList cannot be null, but a MutableList? might be null.

Normally, to call a function on an object, you use a ..

One option for calling a function on a variable, parameter, or property that is
of a nullable type is to use ?.. Then, one of two things will happen:

If the value is null, your function call is ignored, and null is the
result

If the value is not null, your function call is made as normal

So, in your case:

If somevariable.value is null, the add() call is skipped

If somevariable.value is not null, the add() call is made on whatever somevariable.value is

answered Nov 23 '18 at 21:45

CommonsWare

773k13918891936

one possibly should also take !! for @NonNull into account.

– Martin Zeitler
Nov 23 '18 at 22:32

there is a book, already: kotlinlang.org/docs/reference/null-safety.html

– Martin Zeitler
Nov 23 '18 at 22:38

Thank you - I haven't delved into Kotlin yet even though I know I should be so this check threw me off. I can clearly see the value of Kotlin.

– lostScriptie
Nov 24 '18 at 17:07

add a comment |

Kotlin treats null as something more than the source of null-pointer exceptions.

In your code snippet, somevariable.value is of a "nullable type", such as MutableList? or Axolotl?. A MutableList cannot be null, but a MutableList? might be null.

Normally, to call a function on an object, you use a ..

One option for calling a function on a variable, parameter, or property that is
of a nullable type is to use ?.. Then, one of two things will happen:

If the value is null, your function call is ignored, and null is the
result

If the value is not null, your function call is made as normal

So, in your case:

If somevariable.value is null, the add() call is skipped

If somevariable.value is not null, the add() call is made on whatever somevariable.value is

answered Nov 23 '18 at 21:45

CommonsWare

773k13918891936

Kotlin treats null as something more than the source of null-pointer exceptions.

In your code snippet, somevariable.value is of a "nullable type", such as MutableList? or Axolotl?. A MutableList cannot be null, but a MutableList? might be null.

Normally, to call a function on an object, you use a ..

One option for calling a function on a variable, parameter, or property that is
of a nullable type is to use ?.. Then, one of two things will happen:

If the value is null, your function call is ignored, and null is the
result

If the value is not null, your function call is made as normal

So, in your case:

If somevariable.value is null, the add() call is skipped

If somevariable.value is not null, the add() call is made on whatever somevariable.value is

answered Nov 23 '18 at 21:45

CommonsWare

773k13918891936

answered Nov 23 '18 at 21:45

CommonsWare

773k13918891936

answered Nov 23 '18 at 21:45

CommonsWare

773k13918891936

answered Nov 23 '18 at 21:45

CommonsWare

773k13918891936

one possibly should also take !! for @NonNull into account.

– Martin Zeitler
Nov 23 '18 at 22:32

there is a book, already: kotlinlang.org/docs/reference/null-safety.html

– Martin Zeitler
Nov 23 '18 at 22:38

Thank you - I haven't delved into Kotlin yet even though I know I should be so this check threw me off. I can clearly see the value of Kotlin.

– lostScriptie
Nov 24 '18 at 17:07

add a comment |

one possibly should also take !! for @NonNull into account.

– Martin Zeitler
Nov 23 '18 at 22:32

there is a book, already: kotlinlang.org/docs/reference/null-safety.html

– Martin Zeitler
Nov 23 '18 at 22:38

Thank you - I haven't delved into Kotlin yet even though I know I should be so this check threw me off. I can clearly see the value of Kotlin.

– lostScriptie
Nov 24 '18 at 17:07

one possibly should also take !! for @NonNull into account.

– Martin Zeitler
Nov 23 '18 at 22:32

there is a book, already: kotlinlang.org/docs/reference/null-safety.html

– Martin Zeitler
Nov 23 '18 at 22:38

Thank you - I haven't delved into Kotlin yet even though I know I should be so this check threw me off. I can clearly see the value of Kotlin.

– lostScriptie
Nov 24 '18 at 17:07

add a comment |

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