Scala - Strings


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This chapter takes you through the Scala Strings. In Scala, as in Java, a string is an immutable object, that is, an object that cannot be modified. On the other hand, objects that can be modified, like arrays, are called mutable objects. Strings are very useful objects, in the rest of this section, we present important methods of java.lang.String class.

Creating a String

The following code can be used to create a String −

var greeting = "Hello world!";

or

var greeting:String = "Hello world!";

Whenever compiler encounters a string literal in the code, it creates a String object with its value, in this case, “Hello world!”. String keyword can also be given in alternate declaration as shown above.

Try the following example program.

Example

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

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

Save the above program in Demo.scala. The following commands are used to compile and execute this program.

Command

\>scalac Demo.scala
\>scala Demo

Output

Hello, world!

As mentioned earlier, String class is immutable. String object once created cannot be changed. If there is a necessity to make a lot of modifications to Strings of characters then use String Builder Class available in Scala!.

String Length

Methods used to obtain information about an object are known as accessor methods. One accessor method that can be used with strings is the length() method, which returns the number of characters contained in the string object.

Use the following code segment to find the length of a string −

Example

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

Save the above program in Demo.scala. The following commands are used to compile and execute this program.

Command

\>scalac Demo.scala
\>scala Demo

Output

String Length is : 17

Concatenating Strings

The String class includes a method for concatenating two strings −

string1.concat(string2);

This returns a new string that is string1 with string2 added to it at the end. You can also use the concat() method with string literals, as in −

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

Strings are more commonly concatenated with the + operator, as in −

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

Which results in −

"Hello, world!"

The following lines of code to find string length.

Example

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

Save the above program in Demo.scala. The following commands are used to compile and execute this program.

Command

\>scalac Demo.scala
\>scala Demo

Output

Dot Dot saw I was Tod

Creating Format Strings

You have printf() and format() methods to print output with formatted numbers. The String class has an equivalent class method, format(), that returns a String object rather than a PrintStream object.

Try the following example program, which makes use of printf() method −

Example

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)
   }
}

Save the above program in Demo.scala. The following commands are used to compile and execute this program.

command

\>scalac Demo.scala
\>scala Demo

Output

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

String Interpolation

String Interpolation is the new way to create Strings in Scala programming language. This feature supports the versions of Scala-2.10 and later. String Interpolation: The mechanism to embed variable references directly in process string literal.

There are three types (interpolators) of implementations in String Interpolation.

The ‘s’ String Interpolator

The literal ‘s’ allows the usage of variable directly in processing a string, when you prepend ‘s’ to it. Any String variable with in a scope that can be used with in a String. The following are the different usages of ‘s’ String interpolator.

The following example code snippet for the implementation of ‘s’ interpolator in appending String variable ($name) to a normal String (Hello) in println statement.

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

String interpolater can also process arbitrary expressions. The following code snippet for Processing a String (1 + 1) with arbitrary expression (${1 + 1}) using ‘s’ String interpolator. Any arbitrary expression can be embedded in ‘${}’.

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

Try the following example program of implementing ‘s’ interpolator.

Example

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

Save the above program in Demo.scala. The following commands are used to compile and execute this program.

Command

\>scalac Demo.scala
\>scala Demo

Output

Hello, James
1 + 1 = 2

The ‘ f ’ Interpolator

The literal ‘f’ interpolator allows to create a formatted String, similar to printf in C language. While using ‘f’ interpolator, all variable references should be followed by the printf style format specifiers such as %d, %i, %f, etc.

Let us take an example of append floating point value (height = 1.9d) and String variable (name = “James”) with normal string. The following code snippet of implementing ‘f’ Interpolator. Here $name%s to print (String variable) James and $height%2.2f to print (floating point value) 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

It is type safe (i.e.) the variable reference and following format specifier should match otherwise it is showing error. The ‘ f ’ interpolator makes use of the String format utilities (format specifiers) available in Java. By default means, there is no % character after variable reference. It will assume as %s (String).

‘raw’ Interpolator

The ‘raw’ interpolator is similar to ‘s’ interpolator except that it performs no escaping of literals within a string. The following code snippets in a table will differ the usage of ‘s’ and ‘raw’ interpolators. In outputs of ‘s’ usage ‘\n’ effects as new line and in output of ‘raw’ usage the ‘\n’ will not effect. It will print the complete string with escape letters.

‘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

String Methods

Following is the list of methods defined by java.lang.String class and can be used directly in your Scala programs −

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.



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