How to run code if object is null?

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In Kotlin, I can run code if an object is not null like this:

data?.let {
    ... // execute this block if not null
}

but how can I execute a block of code if the object is null?

Just use a normal if:

if (data == null) {
  // Do something
}

Java: How to check if object is null?, In case the image cannot be retrieved another local image should be used. While trying to execute the following lines: Drawable drawable =  How to run code if object is null? Ask Question Asked 2 years, 9 months ago. Active 7 months ago. In Kotlin, I can run code if an object is not null like this:

How to Check for null in JavaScript, Because of a historical bug, typeof null in JavaScript returns "object" that will notify us when the page is ready, and then running the script. I'm pretty sure this doesn't work with the type's own methods, so I doubt it would work with extension methods either. I believe the best way to check if an object is null is obj is null. Unfortunately, to check if an object is not not null requires wrapping in parentheses, which is unfortunate. – natiiix Jun 24 '19 at 12:13

You can create an infix function like this:

infix fun Any?.ifNull(block: () -> Unit) { 
  if (this == null) block()
}

Then you can do this:

data ifNull {
  // Do something
}

?.let vs if not null, There is an simple if (variable != null) statement inside? :smiley: I just made They are logic inference rules dressed up as Kotlin-like code. The problem with The actual difference is whether the receiver object is copied or not. “?.let” copies​  Well, first we have to check if the movie object is null, and if it is, return a not found. And the problem is, by the signature of the method alone you can't tell. But go ahead and read the last phrase of the documentation in the above image. See, there's some documentation to tell you that it may return a null value.

Here's a concise syntax using the Elvis operator. Recall the Elvis operator only executes the right side if the left side evaluates to null.

data ?: doSomething()

Idioms, A collection of random and frequently used idioms in Kotlin. If you have a execute this block if not null This can be effectively combined with other idioms, leading to shorter code. Calling multiple methods on an object instance ( with ). There is another possible scenario I have just come across. I did an ajax call and got data back as null, in a string format. I had to check it like this:

You can use below code

myNullable?.let {

} ?: { 
    // do something
}()

also you can omit fun()

myNullable?.let {

} ?: fun() { 
    // do something
}()

or you can call invoke() instead of ()

myNullable?.let {

} ?: fun() { 
    // do something
}.invoke()

Note that returning value differs like below.

val res0 = myNullable?.let {
} ?: () {

}()
val res1 = myNullable?.let {
} ?: fun() {
    "result"    
}()
val res2 = myNullable?.let {
} ?: () {
    "result"    
}()


println("res0:$res0")
println("res1:$res1")
println("res2:$res2")

RESULT:

res0:kotlin.Unit // () {} with empty
res1:kotlin.Unit // fun() {}
res2:result      // () {} with return

Avoid Check for Null Statement in Java, An aggressively safe strategy could be to check null for every object. This, however, causes a lot of redundant null checks and makes our code  a second If statement was created off the object =If(not(isnull(class1));class1) and this was saved as a detail and linked back to its parent query, and saved as say Classification 1

Better null-checking in Java, Java runs some of the largest sites and platforms in the world but I've the JVM attempts to dereference a variable and finds null instead of an object. If there were other code that used the out variable later, it would have to  The best approach here would be to add an interface for the object forcing the implementation of a null check method. Inside of the implemented null check method you would then add your logic to see if the item properties are null or not.

Null Object Pattern in Java, The null object design pattern describes the uses of null objects and ifPresent() : This enables us to run code on the wrapped value if it is  The name null object may be a bit misleading – the AnonymousUser object is very much an object and not “null”. However, when we define the user by default as AnonymousUser, instead of the value null, it represents the same thing.

is_null - Manual, is_null — Finds whether a variable is NULL Returns TRUE if var is null, FALSE otherwise. is_object() - Finds whether a variable is an object; is_array() - Finds whether a variable is an array People usually write very bad and slow code.

Comments
  • Be careful, if let {} returns null, both blocks would run!
  • apply {} would be safer.
  • @SillyFreak yes it is, i have a logic problem because of this
  • This would run ifNull { } only if data is null?
  • I like this when all you really want to do is test for null and do something then exit.
  • Be careful with this approach, because something.ifNull{} will work, whilst something?.ifNull{} is not gonnna be called!