Sunday, March 08, 2009

String handling in Groovy

This blog post shows through a simple example, how to manage strings in Groovy. Here are a few things which are different in Groovy strings:
  • Groovy strings can be enclosed within

    • single quotes: 'this is a string'

    • double quotes: "this is a string"

    • triple (single or double) quotes: '''this is a string''' and """so is this"""

  • Groovy has something called GStrings which uses replacement variables
  • Groovy makes it easier to use strings in regular expressions

  • The == operator in Groovy actually invokes the equals() method

  • Groovy overloads the +, -, and * operators in Strings



With these concepts in mind the example below should be self explanatory. Try running this example yourself and see the output. After that change the source and see how it affects the output.


//Groovy allows single quoted strings
def string1 = 'hello world'
println string1

//Groovy allows double quoted strings (GStrings have to be double quoted)
def string2 = "Hello World"
println string2

//Groovy has something called GStrings which are regular strings which can
//contain replacement variables. These can be variables, or expressions.
//GStrings have to be double quoted
def gstring = "${string2} is so outdated now!"
println gstring

//GStrings can contain expressions and they are a separate datatype in Java
println "2 + 2 = ${2+2}"
println "GString is a separate datatype in Groovy: ${gstring.class.getName()}"

//multiline strings should be enclosed within triple (single or double) quotes
//Notice how the newline character and leading spaces in lines 2 and 3 are taken
//as part of the string
def multilineString1 = """This is a really long multiline String.
In Java we would have to break up such
String into multiple Strings"""

def multilineString2 = '''This is a really long multiline String.
In Java we would have to break up such
String into multiple Strings'''

println multilineString1
println multilineString2

//In Groovy Strings can also be enclosed within / /, These are used in regular
//expressions because the backslash character does not need to be escaped in
//such Strings
def slashyString1 = / This String does not need to escape the \ character. /
def slashyString2 = / Even \n does not represent a newline /
println slashyString1 + ' ' + slashyString2

//Use == for String comparisons. Also note that double quoted Strings can
//contain single quotes
println "Is '${string1}' == '${string2}' : " + (string1 == string2)

//Groovy supports operator overloading
println 'Hello ' + "World"

//* repeats the String n times
println 'Hello ' * 3 + 'World'

//- removes the specifies substring starting from the left
println string1 - 'world'
println string1 - 'hello'
def stringOps = 'hello ' * 3 + ' world'
println stringOps - 'hello'

//Thankfully the divide operator is not supported with Strings
//println stringOps / 'hello'

//String can be directlt tokenized. We get a List type as the return
def list = multilineString1.tokenize("\n")

//Even though we will learn about ranges and lists later, here is a small
//example which shows how we can treat Strings like ranges and lists

//A String can also be accessed like a list with the [] operator
println string1[0]

//Strings can also be treated as ranges
println string1[1..5]

//ranges can also accept negative values
println string1[-5..-1]

//Strings can be centered for printing
println "'" + string1.center(25) + "'"

//The String class overrides the << string3 =" string1">

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