Scala-字符串 - 芒果文档

📌 相关文章

📜 Scala-字符串

📅 最后修改于: 2020-11-02 04:46:21 🧑 作者: Mango

本章将带您了解Scala字符串。与Java中一样，在Scala中，字符串是不可变的对象，即无法修改的对象。另一方面，可以修改的对象(例如数组)称为可变对象。字符串是非常有用的对象，在本节的其余部分中，我们介绍java.lang.String类的重要方法。

创建一个字符串

以下代码可用于创建字符串-

var greeting = "Hello world!";

or

var greeting:String = "Hello world!";

每当编译器在代码中遇到字符串字面量，编译器都会使用其值(在本例中为“ Hello world！”)创建一个String对象。字符串关键字也可以在替代声明中给出，如上所示。

请尝试以下示例程序。

例

object Demo {
   val greeting: String = "Hello, world!"

   def main(args: Array[String]) {
      println( greeting )
   }
}

将以上程序保存在Demo.scala中。以下命令用于编译和执行该程序。

命令

\>scalac Demo.scala
\>scala Demo

输出

Hello, world!

如前所述，String类是不可变的。字符串对象一旦创建就无法更改。如果有必要做出了很多修改的字符的字符串，然后使用字符串构建类提供斯卡拉！

弦长

用于获取有关对象的信息的方法称为访问器方法。可以与字符串一起使用的一种访问器方法是length()方法，该方法返回字符串对象中包含的字符数。

使用以下代码段查找字符串的长度-

例

object Demo {
   def main(args: Array[String]) {
      var palindrome = "Dot saw I was Tod";
      var len = palindrome.length();
      
      println( "String Length is : " + len );
   }
}

将以上程序保存在Demo.scala中。以下命令用于编译和执行该程序。

命令

\>scalac Demo.scala
\>scala Demo

输出

String Length is : 17

连接字符串

String类包含用于连接两个字符串的方法-

string1.concat(string2);

这将返回一个新的字符串，该字符串为string1，最后添加了string2。您还可以将concat()方法与字符串字面量，如-

"My name is ".concat("Zara");

字符串通常与＆plus;连接在一起。运算符，如-

"Hello," + " world" + "!"

这导致-

"Hello, world!"

以下代码行可查找字符串长度。

例

object Demo {
   def main(args: Array[String]) {
      var str1 = "Dot saw I was ";
      var str2 =  "Tod";
      
      println("Dot " + str1 + str2);
   }
}

将以上程序保存在Demo.scala中。以下命令用于编译和执行该程序。

命令

\>scalac Demo.scala
\>scala Demo

输出

Dot Dot saw I was Tod

创建格式字符串

您可以使用printf()和format()方法来打印带有格式化数字的输出。 String类具有等效的类方法format()，该方法返回String对象而不是PrintStream对象。

尝试以下示例程序，该示例程序使用printf()方法-

例

object Demo {
   def main(args: Array[String]) {
      var floatVar = 12.456
      var intVar = 2000
      var stringVar = "Hello, Scala!"
      
      var fs = printf("The value of the float variable is " + "%f, while the value of the integer " + "variable is %d, and the string" + "is %s", floatVar, intVar, stringVar);
      
      println(fs)
   }
}

将以上程序保存在Demo.scala中。以下命令用于编译和执行该程序。

命令

\>scalac Demo.scala
\>scala Demo

输出

The value of the float variable is 12.456000, 
while the value of the integer variable is 2000, 
and the string is Hello, Scala!()

字符串插值

字符串插值是使用Scala编程语言创建字符串的新方法。此功能支持Scala-2.10及更高版本。字符串插值：将变量引用直接嵌入过程字符串字面量。

字符串插值中有三种实现类型(插值器)。

‘s’字符串内插器

字面量“ s”允许在将“ s”添加到字符串直接在处理字符串时使用变量。具有可以在String中使用的作用域的任何String变量。以下是’s’字符串插值器的不同用法。

以下示例代码片段用于在将字符串变量($ name)附加到println语句中的普通字符串(Hello)时，实现’s’插值器。

val name = “James”
println(s “Hello, $name”) //output: Hello, James

字符串插值器也可以处理任意表达式。以下代码段用于使用’s’字符串插值器处理具有任意表达式($ {1 + 1})的字符串(1 + 1)。任何任意表达式都可以嵌入到’$ {}’中。

println(s “1 + 1 = ${1 + 1}”) //output: 1 + 1 = 2

尝试使用以下示例程序来实现’s’插值器。

例

object Demo {
   def main(args: Array[String]) {
      val name = "James"
      
      println(s"Hello, $name")
      println(s"1 + 1 = ${1 + 1}")
   }
}

将以上程序保存在Demo.scala中。以下命令用于编译和执行该程序。

命令

\>scalac Demo.scala
\>scala Demo

输出

Hello, James
1 + 1 = 2

插值器

字面量“ f”插补器允许创建格式化的字符串，类似于C语言中的printf。使用’f’插值器时，所有变量引用后均应带有printf样式格式说明符，例如％d，％i，％f等。

让我们举一个示例，将浮点值(高度= 1.9d)和字符串变量(名称=“ James”)附加到普通字符串。以下实现“ f”插值器的代码段。这里打印$ name％s(字符串变量)James，打印$ height％2.2f(浮点值)1.90。

val height = 1.9d
val name = "James"
println(f"$name%s is $height%2.2f meters tall") //James is 1.90 meters tall

类型安全(即)变量引用和以下格式说明符应匹配，否则将显示错误。 ‘f’插值器利用Java中可用的String格式实用程序(格式说明符)。默认情况下，变量引用后没有％字符。它将假定为％s(字符串)。

原始插值器

‘原始’插值器与”插值器类似，不同之处在于它不对字符串内的字面量进行转义。下表中的以下代码片段将不同“ s”和“ raw”插值器的用法。在’s’用法的输出中，\ n作为新行起作用，而在’raw’用法的输出中，’\ n’不起作用。它将打印带有转义字母的完整字符串。

‘s’ interpolator usage	‘raw’ interpolator usage
Program − object Demo { def main(args: Array[String]) { println(s"Result = \n a \n b") } }	Program − object Demo { def main(args: Array[String]) { println(raw"Result = \n a \n b") } }
Output − Result = a b	Output − Result = \n a \n b

‘s’ interpolator usage

‘raw’ interpolator usage

Program −

object Demo {
   def main(args: Array[String]) {
      println(s"Result = \n a \n b")
   }
}

Program −

object Demo {
   def main(args: Array[String]) {
      println(raw"Result = \n a \n b")
   }
}

Output −

Result =
a
b

Output −

Result = \n a \n b

字符串方法

以下是java.lang.String类定义的方法列表，可以在您的Scala程序中直接使用-

Sr.No	Methods with Description
1	char charAt(int index) Returns the character at the specified index.
2	int compareTo(Object o) Compares this String to another Object.
3	int compareTo(String anotherString) Compares two strings lexicographically.
4	int compareToIgnoreCase(String str) Compares two strings lexicographically, ignoring case differences.
5	String concat(String str) Concatenates the specified string to the end of this string.
6	boolean contentEquals(StringBuffer sb) Returns true if and only if this String represents the same sequence of characters as the specified StringBuffer.
7	static String copyValueOf(char[] data) Returns a String that represents the character sequence in the array specified.
8	static String copyValueOf(char[] data, int offset, int count) Returns a String that represents the character sequence in the array specified.
9	boolean endsWith(String suffix) Tests if this string ends with the specified suffix.
10	boolean equals(Object anObject) Compares this string to the specified object.
11	boolean equalsIgnoreCase(String anotherString) Compares this String to another String, ignoring case considerations.
12	byte getBytes() Encodes this String into a sequence of bytes using the platform’s default charset, storing the result into a new byte array.
13	byte[] getBytes(String charsetName) Encodes this String into a sequence of bytes using the named charset, storing the result into a new byte array.
14	void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) Copies characters from this string into the destination character array.
15	int hashCode() Returns a hash code for this string.
16	int indexOf(int ch) Returns the index within this string of the first occurrence of the specified character.
17	int indexOf(int ch, int fromIndex) Returns the index within this string of the first occurrence of the specified character, starting the search at the specified index.
18	int indexOf(String str) Returns the index within this string of the first occurrence of the specified substring.
19	int indexOf(String str, int fromIndex) Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.
20	String intern() Returns a canonical representation for the string object.
21	int lastIndexOf(int ch) Returns the index within this string of the last occurrence of the specified character.
22	int lastIndexOf(int ch, int fromIndex) Returns the index within this string of the last occurrence of the specified character, searching backward starting at the specified index.
23	int lastIndexOf(String str) Returns the index within this string of the rightmost occurrence of the specified substring.
24	int lastIndexOf(String str, int fromIndex) Returns the index within this string of the last occurrence of the specified substring, searching backward starting at the specified index.
25	int length() Returns the length of this string.
26	boolean matches(String regex) Tells whether or not this string matches the given regular expression.
27	boolean regionMatches(boolean ignoreCase, int toffset, String other, int offset, int len) Tests if two string regions are equal.
28	boolean regionMatches(int toffset, String other, int offset, int len) Tests if two string regions are equal.
29	*String replace(char oldChar, char newChar)* Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.
30	String replaceAll(String regex, String replacement Replaces each substring of this string that matches the given regular expression with the given replacement.
31	String replaceFirst(String regex, String replacement) Replaces the first substring of this string that matches the given regular expression with the given replacement.
32	String[] split(String regex) Splits this string around matches of the given regular expression.
33	String[] split(String regex, int limit) Splits this string around matches of the given regular expression.
34	boolean startsWith(String prefix) Tests if this string starts with the specified prefix.
35	boolean startsWith(String prefix, int toffset) Tests if this string starts with the specified prefix beginning a specified index.
36	CharSequence subSequence(int beginIndex, int endIndex) Returns a new character sequence that is a subsequence of this sequence.
37	String substring(int beginIndex) Returns a new string that is a substring of this string.
38	String substring(int beginIndex, int endIndex) Returns a new string that is a substring of this string.
39	char[] toCharArray() Converts this string to a new character array.
40	String toLowerCase() Converts all of the characters in this String to lower case using the rules of the default locale.
41	String toLowerCase(Locale locale) Converts all of the characters in this String to lower case using the rules of the given Locale.
42	String toString() This object (which is already a string!) is itself returned.
43	String toUpperCase() Converts all of the characters in this String to upper case using the rules of the default locale.
44	String toUpperCase(Locale locale) Converts all of the characters in this String to upper case using the rules of the given Locale.
45	String trim() Returns a copy of the string, with leading and trailing whitespace omitted.
46	static String valueOf(primitive data type x) Returns the string representation of the passed data type argument.