blocks|key|108004|text|在Kotlin中，if语句是表达式。因此，以下代码是等效的：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|108005|if+(a)+b+else+c|code-block|syntax|javascript|108006|表达式和语句之间的区别在这里很重要。在Java/C#/JavaScript中，if形成一个语句，这意味着它不会解析为一个值。更具体地说，您不能将其赋值给变量。|108007|//+Valid+Kotlin,+but+invalid+Java/C#/JavaScript
var+v+=+if+(a)+b+else+c|108008|如果您来自一种使用if作为语句的语言，这可能看起来不自然，但这种感觉很快就会平息下来。|108009|entityMap^0|9|2|0|0|13|2|0|0|9|2|0^^$0|@$1|2|3|4|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@]|E|$]]|$1|M|3|N|5|H|7|Z|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|13|8|@]|D|@]|E|$]]]|R|$]]

In Kotlin, <code>if</code> statements are expressions. So the following code is equivalent:

<pre><code>if (a) b else c
</code></pre>

The distinction between expression and statement is important here. In Java/C#/JavaScript, <code>if</code> forms a statement, meaning that it does not resolve to a value. More concretely, you can't assign it to a variable.

<pre><code>// Valid Kotlin, but invalid Java/C#/JavaScript
var v = if (a) b else c
</code></pre>

If you're coming from a language where <code>if</code> is a statement, this might seem unnatural but that feeling should soon subside.

blocks|key|325246|text|对于我自己，我使用以下扩展函数：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|325247|fun+T?.or<T>(default:+T):+T+=+if+(this+==+null)+default+else+this+
fun+T?.or<T>(compute:+()+->+T):+T+=+if+(this+==+null)+compute()+else+this|code-block|syntax|javascript|325248|第一个函数将在object等于null的情况下返回所提供的默认值。Second将在相同的情况下计算lambda中提供的表达式。|325249|用法：|325250|1)+e?.getMessage().or("unknown")
2)+obj?.lastMessage?.timestamp.or+{+Date()+}|325251|就我个人而言，上面的代码比if构造内联更具可读性|offset|length|style|CODE|325252|entityMap^0|0|0|0|0|0|D|2|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|X|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|Z|8|@$O|10|P|11|Q|R]]|9|@]|A|$]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

For myself I use following extension functions:

<pre><code>fun T?.or&lt;T&gt;(default: T): T = if (this == null) default else this 
fun T?.or&lt;T&gt;(compute: () -&gt; T): T = if (this == null) compute() else this
</code></pre>

First one will return provided default value in case object equals null. Second will evaluate expression provided in lambda in the same case.

Usage:

<pre><code>1) e?.getMessage().or("unknown")
2) obj?.lastMessage?.timestamp.or { Date() }
</code></pre>

Personally for me code above more readable than <code>if</code> construction inlining

blocks|key|325466|text|一些在其他答案中没有提到的角落案例。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|325467|由于takeIf出现在Kotlin+1.1中，因此三元运算符a+?+b+:+c也可以表示为：|offset|length|style|CODE|325468|b.takeIf+{+a+}+?:+c|code-block|syntax|javascript|325469|如果c为null，则会变得更短。|325470|b.takeIf+{+a+}|325471|还要注意，在Java语言世界中，通常情况下，像value+!=+null+?+value+:+defaultValue这样的null检查只会将in+Kotlin中的null转换为value+?:+defaultValue。|325472|可以将类似的a+!=+null+?+b+:+c转换为a?.let+{+b+}+?:+c。|325473|entityMap|0|LINK|mutability|MUTABLE|url|https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/take-if.html|1|https://kotlinlang.org/docs/reference/whatsnew11.html#also-takeif-and-takeunless^0|0|U|9|2|6|0|B|A|1|0|0|4|4|0|0|N|10|2H|L|0|6|H|Q|H|0^^$0|@$1|2|3|4|5|6|7|14|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|15|8|@$D|16|E|17|F|G]]|9|@$D|18|E|19|1|1A]|$D|1B|E|1C|1|1D]]|A|$]]|$1|H|3|I|5|J|7|1E|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|1F|8|@$D|1G|E|1H|F|G]]|9|@]|A|$]]|$1|O|3|P|5|J|7|1I|8|@]|9|@]|A|$K|L]]|$1|Q|3|R|5|6|7|1J|8|@$D|1K|E|1L|F|G]|$D|1M|E|1N|F|G]]|9|@]|A|$]]|$1|S|3|T|5|6|7|1O|8|@$D|1P|E|1Q|F|G]|$D|1R|E|1S|F|G]]|9|@]|A|$]]|$1|U|3|-4|5|6|7|1T|8|@]|9|@]|A|$]]]|V|$W|$5|X|Y|Z|A|$10|11]]|12|$5|X|Y|Z|A|$10|13]]]]

Some corner cases not mentioned in other answers.

Since appearance of <a href="https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/take-if.html" rel="noreferrer">takeIf</a> in <a href="https://kotlinlang.org/docs/reference/whatsnew11.html#also-takeif-and-takeunless" rel="noreferrer">Kotlin 1.1</a> the ternary operator <code>a ? b : c</code> can also be expressed like this:

<pre><code>b.takeIf { a } ?: c
</code></pre>

This becomes even shorter in case c is <code>null</code>:

<pre><code>b.takeIf { a }
</code></pre>

Also note that typical in Java world null checks like <code>value != null ? value : defaultValue</code> translate in ideomatic Kotlin to just <code>value ?: defaultValue</code>.

Similar <code>a != null ? b : c</code> can be translated to <code>a?.let { b } ?: c</code>.

blocks|key|325531|text|另一种有趣的方法是使用when|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|325532|when(a)+{
++true+->+b
++false+->+c
}|code-block|syntax|javascript|325533|在一些更复杂的场景中可能非常方便。老实说，它比if+...+else+...对我来说更具可读性|325534|entityMap^0|B|4|0|0|N|F|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@$9|T|A|U|B|C]]|D|@]|E|$]]|$1|M|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|N|$]]

Another interesting approach would be to use <code>when</code>:
<pre><code>when(a) {
 true -&gt; b
 false -&gt; c
}
</code></pre>
Can be quite handy in some more complex scenarios. And honestly, it's more readable for me than <code>if ... else ...</code>

blocks|key|325485|text|Java|type|unstyled|depth|inlineStyleRanges|entityRanges|data|325486|int+temp+=+a+?+b+:+c;|code-block|syntax|javascript|325487|相当于Kotlin：|325488|var+temp+=+if+(a)+b+else+c|325489|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Java 

<pre><code>int temp = a ? b : c;
</code></pre>

Equivalent to Kotlin：

<pre><code>var temp = if (a) b else c
</code></pre>

blocks|key|108134|text|替换类C语言的开关运算符。在最简单的形式中，它如下所示|type|unstyled|depth|inlineStyleRanges|entityRanges|data|108135|when+(x)+{
++++1+->+print("x+==+1")
++++2+->+print("x+==+2")
++++else+->+{
++++++++print("x+is+neither+1+nor+2")
++++}
}|code-block|syntax|javascript|108136|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

when replaces the switch operator of C-like languages. In the simplest form it looks like this

<pre><code>when (x) {
 1 -&gt; print("x == 1")
 2 -&gt; print("x == 2")
 else -&gt; {
 print("x is neither 1 nor 2")
 }
}
</code></pre>

blocks|key|108262|text|在Kotlin中没有三元运算符。乍一看，这似乎是个问题。但我认为我们可以使用内联if+else语句来实现，因为这里是表达式。我们要做的就是-|type|unstyled|depth|inlineStyleRanges|entityRanges|data|108263|var+number+=+if(n>0)+"Positive"+else+"Negetive"|code-block|syntax|javascript|108264|在这里，我们可以根据需要阻塞更多的if。就像-|108265|var+number+=+if(n>0)+"Positive"+else+if(n<0)+"Negative"+else+"Zero"|108266|所以这行代码非常简单，而且比三元运算符更具可读性。当我们在java中使用多个三元运算符时，这似乎很可怕。但是这里我们有一个清晰的语法。甚至我们也可以把它写成多行。|108267|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

There is no ternary operator in Kotlin. It seems problematic at the first glance. But think we can do it with inline if else statement because this is expression here. Simply we have to do -

<pre><code>var number = if(n&gt;0) "Positive" else "Negetive"
</code></pre>

Here we can else if block too as many as we need. Like-

<pre><code>var number = if(n&gt;0) "Positive" else if(n&lt;0) "Negative" else "Zero"
</code></pre>

So this line is so simple and much readable than ternary operator. when we use more than one ternary operator in java it seems horrible. But here we have a clear syntax. even we can write it in multiple line too.

blocks|key|108737|text|Kotlin没有三元运算符。您可以使用正则if表达式，如下所示：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|108738|if+(condition)+exp1+else+exp2|108739|此外，除了Kotlin中的if不是语句而是表达式(即它的计算结果是一个值)这一事实之外，在if分支的主体(或else或else+if的主体)中有多个语句的情况下，块的最后一行就是该分支的值。例如：|108740|if+(a>b)+{
++++println("a+is+greater+than+b")
++++a+//+value+of+this+if
}+else+{
++++println("b+is+greater+than+a")
++++b+//+value+of+else
}|code-block|syntax|javascript|108741|entityMap^0|L|2|0|0|T|0|D|2|19|2|1I|4|1N|7|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@$9|U|A|V|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]]|D|@]|E|$]]|$1|J|3|K|5|L|7|15|8|@]|D|@]|E|$M|N]]|$1|O|3|-4|5|6|7|16|8|@]|D|@]|E|$]]]|P|$]]

Kotlin doesn't have a ternary operator. You can use the regular <code>if</code> expression as shown below:
<code>if (condition) exp1 else exp2</code>
Also in addition to the fact that <code>if</code> in Kotlin is not a statement but an expression (i.e. it evaluates to a value), in the case where you have multiple statements inside the body of an <code>if</code> branch (or the body of <code>else</code> or <code>else if</code>), the last line of the block is the value of that branch. For example:
<pre><code>if (a&gt;b) {
 println(&quot;a is greater than b&quot;)
 a // value of this if
} else {
 println(&quot;b is greater than a&quot;)
 b // value of else
}
</code></pre>

blocks|key|108652|text|您可以使用var+a=+if+(a)+b+else+c代替三元运算符。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|108653|kotlin的另一个很好的概念是Elvis+operater。您不需要每次都检查null。|108654|val+l+=+b?.length+?:+-1|code-block|syntax|javascript|108655|如果b不为空，这将返回长度，否则将执行右侧语句。|108656|entityMap^0|5|M|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|U|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|V|8|@]|D|@]|E|$]]|$1|O|3|-4|5|6|7|W|8|@]|D|@]|E|$]]]|P|$]]

You can use <code>var a= if (a) b else c</code> in place of the ternary operator.

Another good concept of kotlin is Elvis operater. You don't need to check null every time.

<pre><code>val l = b?.length ?: -1
</code></pre>

This will return length if b is not null otherwise it executes right side statement.

blocks|key|325377|text|正如Drew+Noake所引用的，kotlin使用if语句作为表达式，因此不再需要三元条件运算符，|type|unstyled|depth|inlineStyleRanges|entityRanges|data|325378|但是使用扩展函数和中缀重载，您可以自己实现它，下面是一个示例|325379|infix+fun+<T>+Boolean.then(value:+T?)+=+TernaryExpression(this,+value)

class+TernaryExpression<out+T>(val+flag:+Boolean,+val+truly:+T?)+{
++++infix+fun+<T>+or(falsy:+T?)+=+if+(flag)+truly+else+falsy
}|code-block|syntax|javascript|325380|然后像这样使用它|325381|val+grade+=+90
val+clazz+=+(grade+>+80)+then+"A"+or+"B"|325382|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

as Drew Noakes quoted, kotlin use if statement as expression, 
so Ternary Conditional Operator is not necessary anymore,

but with the extension function and infix overloading, you could implement that yourself, here is an example

<pre><code>infix fun &lt;T&gt; Boolean.then(value: T?) = TernaryExpression(this, value)

class TernaryExpression&lt;out T&gt;(val flag: Boolean, val truly: T?) {
 infix fun &lt;T&gt; or(falsy: T?) = if (flag) truly else falsy
}
</code></pre>

then use it like this

<pre><code>val grade = 90
val clazz = (grade &gt; 80) then "A" or "B"
</code></pre>

blocks|key|325782|text|在Kotlin中没有三元运算，但有一些有趣的方法来解决这一问题。正如其他人所指出的，直接翻译成Kotlin应该是这样的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|325783|val+x+=+if+(condition)+result1+else+result2|code-block|syntax|javascript|325784|但是，就我个人而言，我认为这可能会变得有点混乱和难以阅读。库中还内置了一些其他选项。您可以将takeIf+{}与elvis运算符一起使用：|325785|val+x+=+result1.takeIf+{+condition+}+?:+result2|325786|这里发生的情况是，takeIf+{}命令返回result1或null，elvis操作符处理null选项。还有一些额外的选项，例如takeUnless+{+}：|325787|val+x+=+result1.takeUnless+{+condition+}+?:+result2|325788|语言很清楚，你知道它在做什么。|325789|如果这是一个常用的条件，你也可以做一些有趣的事情，比如使用内联扩展方法。例如，假设我们想要跟踪一个Int类型的游戏分数，并且如果不满足给定的条件，我们希望总是返回0：|325790|inline+fun+Int.zeroIfFalse(func:+()+->+Boolean)+:+Int+=+if+(!func.invoke())+0+else+this+++++|325791|好吧，这看起来很丑陋。但考虑一下它在使用时的外观：|325792|var+score+=+0
val+twoPointer+=+2
val+threePointer+=+3

score+%2B=+twoPointer.zeroIfFalse+{+scoreCondition+}+
score+%2B=+threePointer.zeroIfFalse+{+scoreCondition+}+|325793|正如您所看到的，Kotlin为您选择如何表达代码提供了很大的灵活性。我的例子有无数的变体，可能我甚至还没有发现一些方法。我希望这能帮到你!|325794|entityMap^0|0|0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|14|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|15|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|16|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|17|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|18|8|@]|9|@]|A|$]]|$1|Q|3|R|5|6|7|19|8|@]|9|@]|A|$]]|$1|S|3|T|5|D|7|1A|8|@]|9|@]|A|$E|F]]|$1|U|3|V|5|6|7|1B|8|@]|9|@]|A|$]]|$1|W|3|X|5|D|7|1C|8|@]|9|@]|A|$E|F]]|$1|Y|3|Z|5|6|7|1D|8|@]|9|@]|A|$]]|$1|10|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]]|11|$]]

There is no ternary operation in Kotlin, but there are some fun ways to work around that. As others have pointed out, a direct translation into Kotlin would look like this:

<pre><code>val x = if (condition) result1 else result2
</code></pre>

But, personally, I think that can get a bit cluttered and hard to read. There are some other options built into the library. You can use takeIf {} with an elvis operator:

<pre><code>val x = result1.takeIf { condition } ?: result2
</code></pre>

What is happening there is that the takeIf { } command returns either your result1 or null, and the elvis operator handles the null option. There are some additional options, takeUnless { }, for example:

<pre><code>val x = result1.takeUnless { condition } ?: result2
</code></pre>

The language is clear, you know what that's doing. 

If it's a commonly used condition, you could also do something fun like use an inline extension method. Let's assume we want to track a game score as an Int, for example, and we want to always return 0 if a given condition is not met:

<pre><code>inline fun Int.zeroIfFalse(func: () -&gt; Boolean) : Int = if (!func.invoke()) 0 else this 
</code></pre>

Ok, that seems ugly. But consider how it looks when it is used:

<pre><code>var score = 0
val twoPointer = 2
val threePointer = 3

score += twoPointer.zeroIfFalse { scoreCondition } 
score += threePointer.zeroIfFalse { scoreCondition } 
</code></pre>

As you can see, Kotlin offers a lot of flexibility in how you choose to express your code. There are countless variations of my examples and probably ways I haven't even discovered yet. I hope this helps!

blocks|key|325948|text|你可以这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|325949|val+ans+=+(exp1+==+exp2)+then+"yes"+?:+"no"|code-block|syntax|javascript|325950|通过使用此扩展：|325951|infix+fun<T>+Boolean.then(first:+T):+T?+=+if+(this)+first+else+null|325952|附言:不要修改上面的中缀函数来接受first:+T?，表达式在逻辑上会变得不正确。例如:如果你修改它以接受可以为空的first:+T?，那么val+ans+=+(true+==+true)+then+null+?:+"abcd"，ans将是"abcd"，这是不正确的。|offset|length|style|CODE|325953|entityMap^0|0|0|0|0|H|9|1M|9|1Y|18|37|3|3C|6|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]|$M|Z|N|10|O|P]|$M|11|N|12|O|P]|$M|13|N|14|O|P]|$M|15|N|16|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|17|8|@]|9|@]|A|$]]]|R|$]]

You can do something like this:
<pre><code>val ans = (exp1 == exp2) then &quot;yes&quot; ?: &quot;no&quot;
</code></pre>
by using this extension:
<pre><code>infix fun&lt;T&gt; Boolean.then(first: T): T? = if (this) first else null
</code></pre>
P.S: Dont modify above infix function to accept <code>first: T?</code>, the expression will become logically incorrect. Eg: If you modify it to accept nullable <code>first: T?</code>, then <code>val ans = (true == true) then null ?: &quot;abcd&quot;</code>, <code>ans</code> will be <code>&quot;abcd&quot;</code>, which would not be correct.

blocks|key|325865|text|如果您不知道如何使用标准表示法，您也可以使用infix创建/模拟它，如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|325866|创建一个类来保存你的目标和结果：|325867|data+class+Ternary<T>(val+target:+T,+val+result:+Boolean)|code-block|syntax|javascript|325868|创建一些infix函数来模拟三元运算|325869|infix+fun+<T>+Boolean.then(target:+T):+Ternary<T>+{
++++return+Ternary(target,+this)
}

infix+fun+<T>+Ternary<T>.or(target:+T):+T+{
++++return+if+(this.result)+this.target+else+target
}|325870|然后你就可以像这样使用它：|325871|val+collection:+List<Int>+=+mutableListOf(1,+2,+3,+4)

var+exampleOne+=+collection.isEmpty()+then+"yes"+or+"no"
var+exampleTwo+=+(collection.isNotEmpty()+&&+collection.contains(2))+then+"yes"+or+"no"
var+exampleThree+=+collection.contains(1)+then+"yes"+or+"no"|325872|entityMap|0|LINK|mutability|MUTABLE|url|https://kotlinlang.org/docs/reference/functions.html^0|M|5|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@$A|11|B|12|1|13]]|C|$]]|$1|D|3|E|5|6|7|14|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|15|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|16|8|@]|9|@]|C|$]]|$1|M|3|N|5|H|7|17|8|@]|9|@]|C|$I|J]]|$1|O|3|P|5|6|7|18|8|@]|9|@]|C|$]]|$1|Q|3|R|5|H|7|19|8|@]|9|@]|C|$I|J]]|$1|S|3|-4|5|6|7|1A|8|@]|9|@]|C|$]]]|T|$U|$5|V|W|X|C|$Y|Z]]]]

If you do not what to use the standard notation you can also create/simulate it using <a href="https://kotlinlang.org/docs/reference/functions.html" rel="noreferrer">infix</a> with something like this:

create a class to hold your target and result:

<pre><code>data class Ternary&lt;T&gt;(val target: T, val result: Boolean)
</code></pre>

create some infix functions to simulate a ternary operation

<pre><code>infix fun &lt;T&gt; Boolean.then(target: T): Ternary&lt;T&gt; {
 return Ternary(target, this)
}

infix fun &lt;T&gt; Ternary&lt;T&gt;.or(target: T): T {
 return if (this.result) this.target else target
}
</code></pre>

Then you will be able to use it like this: 

<pre><code>val collection: List&lt;Int&gt; = mutableListOf(1, 2, 3, 4)

var exampleOne = collection.isEmpty() then "yes" or "no"
var exampleTwo = (collection.isNotEmpty() &amp;&amp; collection.contains(2)) then "yes" or "no"
var exampleThree = collection.contains(1) then "yes" or "no"
</code></pre>

blocks|key|108509|text|您可以在Kotlin中使用if表达式。在Kotlin中，if是一个带有结果值的表达式。所以在Kotlin中我们可以写|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|108510|fun+max(a:+Int,+b:+Int)+=+if+(a+>+b)+a+else+b|code-block|syntax|javascript|108511|在Java中，我们可以使用更大的代码来实现相同的功能|108512|int+max(int+a,+int+b)+{
return+a+>+b+?+a+:+b
}|108513|entityMap^0|D|2|S|2|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@$9|R|A|S|B|C]|$9|T|A|U|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|V|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|W|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|X|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|P|$]]

You can use <code>if</code> expression for this in Kotlin. In Kotlin <code>if</code> is an expression with a result value. So in Kotlin we can write

<pre><code>fun max(a: Int, b: Int) = if (a &gt; b) a else b
</code></pre>

and in Java we can achieve the same but with larger code

<pre><code>int max(int a, int b) {
return a &gt; b ? a : b
}
</code></pre>

blocks|key|325556|text|另一种简短的使用方法|type|unstyled|depth|inlineStyleRanges|entityRanges|data|325557|val+value+:+String+=+"Kotlin"

value+?:+""|code-block|syntax|javascript|325558|在这里，kotlin自己检查null值，如果是null，则传递空字符串值。|325559|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

Another short approach to use 

<pre><code>val value : String = "Kotlin"

value ?: ""
</code></pre>

Here kotlin itself checks null value and if it is null then it passes empty string value.

blocks|key|325737|text|在使用apply()时，let在处理三元运算时似乎非常方便，因为它更优雅，并为您提供了空间|type|unstyled|depth|inlineStyleRanges|entityRanges|data|325738|val+columns:+List<String>+=+...
val+band+=+Band().apply+{
++++name+=+columns[0]
++++album+=+columns[1]
++++year+=+columns[2].takeIf+{+it.isNotEmpty()+}?.let+{+it.toInt()+}+?:+0
}|code-block|syntax|javascript|325739|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

When working with apply(), let seems very handy when dealing with ternary operations, as it is more elegant and give you room

<pre><code>val columns: List&lt;String&gt; = ...
val band = Band().apply {
 name = columns[0]
 album = columns[1]
 year = columns[2].takeIf { it.isNotEmpty() }?.let { it.toInt() } ?: 0
}
</code></pre>

blocks|key|108622|text|为什么要用这样的东西：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|108623|when(a)+{
++true+->+b
++false+->+b
}|code-block|syntax|javascript|108624|当您可以实际使用这样的内容时(在本例中，a是布尔值)：|offset|length|style|CODE|108625|when+{
++a+->+b
++else+->+b
}|108626|entityMap^0|0|0|K|1|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@$I|T|J|U|K|L]]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

Why would one use something like this:

<pre><code>when(a) {
 true -&gt; b
 false -&gt; b
}
</code></pre>

when you can actually use something like this (<code>a</code> is boolean in this case):

<pre><code>when {
 a -&gt; b
 else -&gt; b
}
</code></pre>

blocks|key|325888|text|在Kotlin中，您可以像这样使用三元运算：val+x+=+if(a)+"add+b"+else+"add+c"|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|325889|entityMap^0|M|Y|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

In Kotlin you can use ternary operation like this: <code>val x = if(a) "add b" else "add c"</code>

blocks|key|325651|text|使用以下infix函数，我可以涵盖许多常见的用例，几乎与在Python中一样：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|325652|class+TestKotlinTernaryConditionalOperator+{

++++@Test
++++fun+testAndOrInfixFunctions()+{
++++++++Assertions.assertThat(true+and+"yes"+or+"no").isEqualTo("yes")
++++++++Assertions.assertThat(false+and+"yes"+or+"no").isEqualTo("no")

++++++++Assertions.assertThat("A"+and+"yes"+or+"no").isEqualTo("yes")
++++++++Assertions.assertThat(""+and+"yes"+or+"no").isEqualTo("no")

++++++++Assertions.assertThat(1+and+"yes"+or+"no").isEqualTo("yes")
++++++++Assertions.assertThat(0+and+"yes"+or+"no").isEqualTo("no")

++++++++Assertions.assertThat(Date()+and+"yes"+or+"no").isEqualTo("yes")
++++++++@Suppress("CAST_NEVER_SUCCEEDS")
++++++++Assertions.assertThat(null+as+Date?+and+"yes"+or+"no").isEqualTo("no")
++++}
}

infix+fun+<E>+Boolean?.and(other:+E?):+E?+=+if+(this+==+true)+other+else+null
infix+fun+<E>+CharSequence?.and(other:+E?):+E?+=+if+(!(this+?:+"").isEmpty())+other+else+null
infix+fun+<E>+Number?.and(other:+E?):+E?+=+if+(this?.toInt()+?:+0+!=+0)+other+else+null
infix+fun+<E>+Any?.and(other:+E?):+E?+=+if+(this+!=+null)+other+else+null
infix+fun+<E>+E?.or(other:+E?):+E?+=+this+?:+other|code-block|syntax|javascript|325653|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

With the following infix functions I can cover many common use cases pretty much the same way it can be done in Python : 

<pre><code>class TestKotlinTernaryConditionalOperator {

 @Test
 fun testAndOrInfixFunctions() {
 Assertions.assertThat(true and "yes" or "no").isEqualTo("yes")
 Assertions.assertThat(false and "yes" or "no").isEqualTo("no")

 Assertions.assertThat("A" and "yes" or "no").isEqualTo("yes")
 Assertions.assertThat("" and "yes" or "no").isEqualTo("no")

 Assertions.assertThat(1 and "yes" or "no").isEqualTo("yes")
 Assertions.assertThat(0 and "yes" or "no").isEqualTo("no")

 Assertions.assertThat(Date() and "yes" or "no").isEqualTo("yes")
 @Suppress("CAST_NEVER_SUCCEEDS")
 Assertions.assertThat(null as Date? and "yes" or "no").isEqualTo("no")
 }
}

infix fun &lt;E&gt; Boolean?.and(other: E?): E? = if (this == true) other else null
infix fun &lt;E&gt; CharSequence?.and(other: E?): E? = if (!(this ?: "").isEmpty()) other else null
infix fun &lt;E&gt; Number?.and(other: E?): E? = if (this?.toInt() ?: 0 != 0) other else null
infix fun &lt;E&gt; Any?.and(other: E?): E? = if (this != null) other else null
infix fun &lt;E&gt; E?.or(other: E?): E? = this ?: other
</code></pre>

blocks|key|108773|text|在Java中，if是一个语句，但在Kotlin中，if是一个表达式。它被称为表达式，因为它比较a和b的值并返回最大值。因此，在Kotlin中没有三元运算符(a>b)-A:B，因为它被if表达式替换。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|108774|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

In Java, if is a statement but, in Kotlin if is an expression. It is called an expression because it compares the values of a and b and returns the maximum value. Therfore, in Kotlin there is no ternary operator (a&gt;b)?a:b because it is replaced by the if expression.

blocks|key|108715|text|如果有人需要隐式类型转换的三元运算符：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|108716|/**'[_t]'+for+ternary+operator*/
@Suppress("FunctionName")
@OptIn(ExperimentalContracts::class)
fun+<T>+_t(bool:+Boolean,+onTrue:+T,+onFalse:+T):+T
{
++++contract+{+returns()+implies+bool+}
++++return+if+(bool)+onTrue+else+onFalse
}|code-block|syntax|javascript|108717|尽管不确定这有多有用|108718|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

In case someone needs ternary operator with implicit casting:
<pre><code>/**'[_t]' for ternary operator*/
@Suppress(&quot;FunctionName&quot;)
@OptIn(ExperimentalContracts::class)
fun &lt;T&gt; _t(bool: Boolean, onTrue: T, onFalse: T): T
{
 contract { returns() implies bool }
 return if (bool) onTrue else onFalse
}
</code></pre>
Although not sure how useful this is

What is the equivalent of this expression in Kotlin?

<pre><code>a ? b : c
</code></pre>

This is not valid code in Kotlin.

Kotlin Ternary Conditional Operator

Python

Kotlin

Java

在Kotlin中，这个表达式的等价物是什么？a ? b : c这不是Kotlin中的有效代码。

问Kotlin三元条件运算符
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回答 21

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