How to set non-null string variable's value to empty if null value passed

Question

How can I achieve this java code's analog in Kotlin?

class Item {
    private String text = "";

    public String getText() {
        return text;
    }

    public void setText(String str) {
        if(str == null){
            text = "";
        } else {
            text = str;
        }
    }

}

So whenever I set null value for text, it's value replaced with empty string. I want exactly the same behavior but in Kotlin, because I'm working with Java classes in Kotlin code, which may return some null values. Checking for nullability everytime before setting fields value is not a good idea, because it can be forgotten by accident, and give an exception at runtime.

Hit Ctrl-shift-A (or Cmd-shift-A on Mac), then type "convert java file to Kotlin". — JB Nizet
– JB Nizet, Commented Apr 22, 2019 at 21:27
What's wrong with an exception at runtime? If you're testing your code thoroughly, it's a lot easier to debug an exception than to debug silently transformed data. — Louis Wasserman
– Louis Wasserman, Commented Apr 22, 2019 at 22:03

Community · Accepted Answer · 2020-06-20 09:12:55Z

7

The simplest way is `text.orEmpty()`

text.orEmpty() for a String? will return "" if null, or the original string

The best alternate option is text ?: ""

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Dec 23, 2019 at 20:23

Gibolt

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Comments

Gustavo Pagani · Accepted Answer · 2019-04-22 22:05:21Z

0

class Item {
    private var text: String = ""

    fun getText() = text

    fun setText(str: String?) {
        text = str ?: ""
    }
}

edited Apr 22, 2019 at 22:05

answered Apr 22, 2019 at 21:41

Gustavo Pagani

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2 Comments

Louis Wasserman Over a year ago

this.text = str ?: "" ?

Alexey Romanov Over a year ago

Make the getter public with private setter instead of getText().

gidds · Accepted Answer · 2019-04-23 11:02:39Z

0

The Java code in the question implements a property whose value can't be null, but whose setter allows null (converting it to a default value). (Java doesn't have direct support for properties, so you have to code the field, getter, and setter by hand.)

This doesn't really have an idiomatic Kotlin equivalent. The direct translation would be:

class Item {
    var text: String = ""
        set(value) { field = value ?: "" }
}

This declares a non-nullable property with a default value. (Like all Kotlin properties, its field is private; it also has a getter method and — because it's a var — a setter method, both of which are public because the no other visibility was specified.) And it overrides the setter to substitute the default value if null is passed.

If called from Java code, then I think the above would handle it as expected. (I haven't tested it.)

But because the Kotlin compiler knows that the field is not nullable, it wouldn't allow you to call the setter with a null value in the first place; this is where it differs from the Java version.

So if it were called only from other Kotlin code, the ?: "" would never be used, and so the setter wouldn't need to be overridden. The most natural Kotlin translation would be simply:

class Item {
    var text: String = ""
}

answered Apr 23, 2019 at 11:02

gidds

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2 Comments

Nur4I Over a year ago

You exactly described my problem. Setter is called only from kotlin code, but the value is taken from Java library, which may return null. So I was searching for elegant way to easily overcome these null values and set empty strings if null passed

gidds Over a year ago

If the setter is called only from Kotlin, then I'd suggest using a simple non-nullable property (as per my last example), and fixing nulls when you call the setter, e.g. myItem.text = someValueFromJava ?: "". (That's concise, and keeps the null handling nearer the Java.) Or, if that happens a lot, perhaps adding a separate method to Item e.g. fun setTextHandlingNull(value: String?) { text = value ?: "" }. (That makes it more obvious to the caller what's happening.)

John De la cruz · Accepted Answer · 2021-04-16 10:02:45Z

0

Some times the IDE will tell you that is unnecesary, so I made function and named ifNull then I passed the value.

    private fun ifNull(value: String?): String {

    return value ?: " "
}

Now, use it like this.

TextView.text = ifNull(name)

answered Apr 16, 2021 at 10:02

John De la cruz

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How to set non-null string variable's value to empty if null value passed

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The simplest way is `text.orEmpty()`

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The simplest way is text.orEmpty()

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The simplest way is `text.orEmpty()`