246 lines
4.0 KiB
Markdown
246 lines
4.0 KiB
Markdown
---
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title: Strings
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localeTitle: 字符串
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---
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# 字符串
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字符串是编程语言中的基本数据类型。字符串由`String`类型表示。字符串是不可变的。 Kotlin有一个丰富的API来处理字符串。
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### 基本用法
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#### 宣言
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```kotlin
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// Explicit type declaration
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var firstName : String = "Elon"
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// or Implicit type declaration and will still compile
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val lastName = "Musk"
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```
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另外，请注意`val`变量类型的用法，以下是它的行为方式
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```kotlin
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firstName = "Mark" // can be changed
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lastName = "Zuckerberg" // cannot be changed
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lastName = 12 // Error: type mismatch
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```
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#### 字符串连接
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显示在代码片段中，就像Java一样，将`Int`追加到 `String`将导致`String`输出
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```kotlin
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var str = "abc" + 1
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println(str + "def")
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```
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输出：
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```shell
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abc1def
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```
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即使没有显式地将`Int`值1显式转换为`String`对象，结果输出仍然是`String` 。
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#### 具有多行的字符串
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程序员可以使用三引号而不是双引号来声明具有多行的`String`变量
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```kotlin
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var str = """
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This is line 1
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This is line 2
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This is line 3
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"""
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println(str)
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```
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输出：
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```shell
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This is line 1
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This is line 2
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This is line 3
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```
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或者使用`.trimIndent()`
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使用`trimIndent()`还可以通过消除每行上多余的和不必要的缩进来提供干净的输出格式。检查下面的代码段：
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```kotlin
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var str = """
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This is line 1
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This is line 2
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This is line 3
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""".trimIndent()
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println(str)
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```
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输出：
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```shell
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This is line 1
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This is line 2
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This is line 3
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```
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### 访问字符串的字符
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#### 索引访问
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程序员可以使用索引访问运算符访问字符串的元素（字符）：
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```kotlin
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var str = "Example"
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println(str[2])
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```
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输出：
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```shell
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a
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```
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就像从数组中访问元素一样，您得到：
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```kotlin
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var str = "Example"
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println(str[9]) // Error: index out of bounds
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```
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#### 通过String迭代
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字符串的元素是可以通过索引操作访问的字符： `s[i]` 。
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```kotlin
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var str = "Example"
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for (c in str) {
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println(c)
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}
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```
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输出：
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```shell
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E
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x
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a
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m
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p
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l
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e
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```
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### 字符串的不变性
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就像Java一样，您无法更改`String`各个元素
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```kotlin
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var str = "Example"
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str[2] = "b" // Error
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```
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#### 重新分配字符串值
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```kotlin
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var str = "Example"
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println(str)
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str = "Example was changed"
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println(str)
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```
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输出：
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```shell
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Example
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Example was changed
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```
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### 字符串属性
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#### 确定字符串的长度
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```kotlin
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var str = "Example"
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println(str.length)
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```
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输出：
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```shell
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7
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```
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### 字符串函数
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这些是当前Kotlin版本中可用的一些常见`String`函数
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### 相比于
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将此对象与指定的对象进行比较以获得顺序。如果此对象等于指定的其他对象，则返回零;如果小于其他对象，则返回负数;如果它大于其他对象，则返回正数。
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```kotlin
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var str = "Example"
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var str2 = "Example123"
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var str3 = "Example12345"
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println(str.compareTo(str2))
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println(str.compareTo(str3))
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println(str3.compareTo(str))
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println(str.compareTo("Example"))
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```
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输出：
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```shell
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-3
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-5
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5
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0 # Equal
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```
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### 等于
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指示`String`对象是否与另一个`String`对象完全相同
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```kotlin
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var str = "Example"
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var str2 = "Example2"
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println(str.equals("Example"))
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println(str2.equals("Example"))
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```
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输出：
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```shell
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true
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false
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```
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### 得到
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返回此字符序列中指定索引处的字符。
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\`\`\`kotlin var str =“示例” 的println（str.get（3））
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```
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Output:
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```
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贝壳 米
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```
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### toString
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Returns a string representation of the object.
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```
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科特林 println（9.toString（）+ 10） println（9 + 10）
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```
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Output:
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```
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贝壳 “910” 19 \`\`\`
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#### 资源
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* [Kotlin基本类型](https://kotlinlang.org/docs/reference/basic-types.html)
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* [Kotlin字符串参考](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin/-string/index.html) |