string Kotlin - 如何正确连接字符串

Kotlin - How to correctly concatenate a String

提问by Daniele

A very basic question, what is the right way to concatenate a String in Kotlin?

一个非常基本的问题，在 Kotlin 中连接字符串的正确方法是什么？

In Java you would use the concat()method, e.g.

在 Java 中，您将使用该concat()方法，例如

String a = "Hello ";
String b = a.concat("World"); // b = Hello World

The concat()function isn't available for Kotlin though. Should I use the +sign?

但是，该concat()功能不适用于 Kotlin。我应该使用这个+标志吗？

回答by Avijit Karmakar

In Kotlin, you can concatenate using string interpolation / templates:

在 Kotlin 中，您可以使用字符串插值/模板进行连接：

val a = "Hello"
val b = "World"
val c = "$a $b"

The output will be: Hello World

输出将是： Hello World

Or you can concatenate using the +/ plus()operator:

或者您可以使用+/plus()运算符进行连接：

val a = "Hello"
val b = "World"
val c = a + b   // same as calling operator function a.plus(b)

print(c)

The output will be: HelloWorld

输出将是： HelloWorld

Or you can concatenate using the StringBuilder.

或者您可以使用StringBuilder.

val a = "Hello"
val b = "World"

val sb = StringBuilder()
sb.append(a).append(b)
val c = sb.toString()

print(c)

The output will be: HelloWorld

输出将是： HelloWorld

回答by Harald Gliebe

kotlin.Stringhas a plusmethod:

kotlin.String有一个plus方法：

a.plus(b)

See https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-string/plus.htmlfor details.

有关详细信息，请参阅https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-string/plus.html。

回答by Tushar

Yes, you can concatenate using a +sign. Kotlin has string templates, so it's better to use them like:

是的，您可以使用+符号进行连接。Kotlin 有字符串模板，所以最好像这样使用它们：

var fn = "Hello"
var ln = "World"

"$fn $ln"for concatenation.

"$fn $ln"用于串联。

You can even use String.plus()method.

你甚至可以使用String.plus()方法。

回答by Rhusfer

I agree with the accepted answer above but it is only good for known string values. For dynamic string values here is my suggestion.

我同意上面接受的答案，但它只适用于已知的字符串值。对于动态字符串值，这是我的建议。

// A list may come from an API JSON like
{
   "persons": {
      "Person 1",
      "Person 2",
      "Person 3",
         ...
      "Person N"
   }
}
var listOfNames = mutableListOf<String>() 

val stringOfNames = listOfNames.joinToString(", ") 
// ", " <- a separator for the strings, could be any string that you want

// Posible result
// Person 1, Person 2, Person 3, ..., Person N

This is useful for concatenating list of strings with separator.

这对于用分隔符连接字符串列表很有用。

回答by CoolMind

Similar to @Rhusfer answerI wrote this. In case you have a group of EditTexts and want to concatenate their values, you can write:

类似于@Rhusfer 的回答我写了这个。如果您有一组EditTexts 并且想要连接它们的值，您可以编写：

listOf(edit_1, edit_2, edit_3, edit_4).joinToString(separator = "") { it.text.toString() }

If you want to concatenate HashMap, use this:

如果要连接HashMap，请使用以下命令：

map.entries.joinToString(separator = ", ")
// Result:
// id=123, name=John, surname=Smith

回答by Licat Julius

Try this, I think this is a natively way to concatenate strings in Kotlin:

试试这个，我认为这是在 Kotlin 中连接字符串的本机方式：

val result = buildString{
    append("a")
    append("b")
}

println(result)

// you will see "ab" in console.

回答by Shradha Sangtani

There are various way to concatenate strings in kotlin Example -

在 kotlin 示例中有多种连接字符串的方法 -

a = "Hello" , b= "World"

1. Using + operator a+b

2. Using plus()operator

   a.plus(b)

1. 使用 + 运算符 a+b

2. 使用plus()运算符

   a.plus(b)

Note - + is internally converted to .plus() method only

注意 - + 仅在内部转换为 .plus() 方法

In above 2 methods, a new string object is created as strings are immutable. if we want to modify the existing string, we can use StringBuilder

在上述 2 种方法中，由于字符串是不可变的，因此创建了一个新的字符串对象。如果我们想修改现有的字符串，我们可以使用 StringBuilder

StringBuilder str = StringBuilder("Hello").append("World")

回答by Kanagalingam

yourString += "newString"

yourString += "newString"

This way you can concatenate a string

这样你就可以连接一个字符串