String

Strings are a fundamental type in any programming language, including Groovy, where they are used extensively for storing and manipulating textual data. This tutorial will help non-programmers understand how to work with strings in Groovy, covering basic concepts, operations, and common methods.

What is a String?

A string in programming is essentially a sequence of characters. In Groovy, like many other languages, strings are enclosed in quotes. You can use either single quotes (') or double quotes ("), but double quotes allow for string interpolation (inserting variable values directly into the string).

Creating Strings

Here’s how you can create a string in Groovy:

def singleQuoteString = 'Hello, world!'
def doubleQuoteString = "Hello, world!"

String Interpolation

One of the powerful features of Groovy is string interpolation, which is the ability to embed expressions within string literals directly. You use ${expression} or just $variableName inside double-quoted strings:

def name = "Alice"
def greeting = "Hello, $name!"
println(greeting)  // Outputs: Hello, Alice!

Common String Methods

Groovy strings have methods that perform various operations, such as changing case, finding substrings, or replacing parts of the string. Here are a few useful methods:

• Length of a string: Returns the number of characters in the string.

  def message = "Hello, world!"
  println(message.length())  // Outputs: 13

• Convert to upper case:

  println(message.toUpperCase())  // Outputs: HELLO, WORLD!

• Convert to lower case:

  println(message.toLowerCase())  // Outputs: hello, world!

• Replace parts of the string:

  println(message.replace("Hello", "Goodbye"))  // Outputs: Goodbye, world!

• Substring: Extracting parts of the string.

  println(message.substring(7))  // Outputs: world!

Concatenation

You can combine strings using the + operator or the string interpolation feature:

def firstName = "John"
def lastName = "Doe"
def fullName = firstName + " " + lastName
println(fullName)  // Outputs: John Doe

Multiline Strings

Groovy also supports multiline strings, which are great for including formatted text without needing to insert newline characters manually:

def lyrics = """Line 1
Line 2
Line 3"""
println(lyrics)

Useful Groovy String Functions

• Trim: Removes whitespace from both ends of a string.

  def extraSpace = "  Hello, world!  "
  println(extraSpace.trim())  // Outputs: Hello, world!

• Starts with and Ends with: Checks if the string starts or ends with a substring.

  println("Groovy".startsWith("Gro"))  // Outputs: true
  println("Groovy".endsWith("vy"))  // Outputs: true

• Contains: Checks if the string contains a certain sequence of characters.

  println("Groovy".contains("oo"))  // Outputs: true

Exercises

Exercise 1: Reverse a String

Task: Write a Groovy script that reverses a string. For example, if the input is "hello", the output should be "olleh".

Exercise 2: Palindrome Checker

Task: Create a function in Groovy that checks whether a string is a palindrome (reads the same backward as forward). For example, "radar" should return true, while "hello" should return false.

Exercise 3: Count Vowels

Task: Write a script that counts the number of vowels in a given string. For instance, in the string "hello world", the output should be 3.

Exercise 4: Concatenate and Capitalize

Task: Given two strings, concatenate them and then convert the entire resulting string to uppercase. For example, "hello" and "world" should become "HELLO WORLD".

Exercise 5: Find and Replace

Task: Create a function that takes a string and replaces all occurrences of the word "Java" with "Groovy". For instance, transforming the string "I love Java" should result in "I love Groovy".

Solutions

Solution to Exercise 1: Reverse a String

def reverseString(String str) {
    return str.reverse()
}

println(reverseString("hello"))  // Outputs: olleh

Solution to Exercise 2: Palindrome Checker

def isPalindrome(String str) {
    return str == str.reverse()
}

println(isPalindrome("radar"))  // Outputs: true
println(isPalindrome("hello"))  // Outputs: false

Solution to Exercise 3: Count Vowels

def countVowels(String str) {
    def vowels = ['a', 'e', 'i', 'o', 'u']
    int count = 0
    str.toLowerCase().each { char ->
        if (char in vowels) {
            count++
        }
    }
    return count
}

println(countVowels("hello world"))  // Outputs: 3

Solution to Exercise 4: Concatenate and Capitalize

def concatenateAndCapitalize(String str1, String str2) {
    return (str1 + " " + str2).toUpperCase()
}

println(concatenateAndCapitalize("hello", "world"))  // Outputs: HELLO WORLD

Solution to Exercise 5: Find and Replace

def replaceJavaWithGroovy(String str) {
    return str.replaceAll("Java", "Groovy")
}

println(replaceJavaWithGroovy("I love Java"))  // Outputs: I love Groovy