Programming for beginners: range operator

You should perform two steps to make the range operator available to custom type.

a. Custom type must implement next and previous methods.

b. Custom type must implement Comparable interface

For example, I had written an EvenNumber class that prints even numbers.

HelloWorld.groovy

class EvenNumber implements Comparable<EvenNumber>{
 int num
 int current
 
 public EvenNumber(int num){
  if(num % 2 != 0){
   this.num = num + 1
   return
  }
  this.num = num
  this.current = this.num
 }

 EvenNumber next(){
  current = current + 2
  return new EvenNumber(current)
 }
 
 EvenNumber previous(){
  current = current - 2
  return new EvenNumber(current)
 }
 
 int compareTo(EvenNumber other){
  return this.num <=> other.num
 }
 
 String toString(){
  return num + ""
 }
}

EvenNumber first = new EvenNumber(10)
EvenNumber last = new EvenNumber(25)

def range = first..last

for(i in range){
 print i.toString() + " "
}

Output

10 12 14 16 18 20 22 24 26

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Range operator (..) is used to create range of objects. Range elements are represented as list internally.

Example

range = 0..10

Above statement defines a range of integers from 0 to 10. Ranges usually has a lower left bound and higher right bound.

HelloWorld.groovy

def range = 0..10                                   

if(range instanceof List){
 println "Range is an instance of list"
 println range
}

Output

Range is an instance of list

0..10

Get number of elements in the range

Use the 'size' method to get the number of elements in the range.

HelloWorld.groovy

def range = 0..10                                   

if(range instanceof List){
 println "Range is an instance of list"
 println range
 println "Number of Elements in the range ${range.size()}"
}

Output

Range is an instance of list

0..10

Number of Elements in the range 11

..< operator

It specifies that the value on the right side is not part of the range.

HelloWorld.groovy

def range = 0..<10

for (i in range){
 println i
}

Output

As you see the output, ..< operator is not included 10 in the range.

You can apply ranges to other types like character and dates etc.,

HelloWorld.groovy

def range = 'a'..'z'

for (i in range){
 print " " + i
}

println ""

def today = new Date()
def tenDaysBefore = today-10
def tenDays = tenDaysBefore..today

for (i in tenDays){
 print " " + i
}

Output

a b c d e f g h i j k l m n o p q r s t u v w x y z

Sat Nov 10 20:28:09 IST 2018 Sun Nov 11 20:28:09 IST 2018 Mon Nov 12 20:28:09 IST 2018 Tue Nov 13 20:28:09 IST 2018 Wed Nov 14 20:28:09 IST 2018 Thu Nov 15 20:28:09 IST 2018 Fri Nov 16 20:28:09 IST 2018 Sat Nov 17 20:28:09 IST 2018 Sun Nov 18 20:28:09 IST 2018 Mon Nov 19 20:28:09 IST 2018 Tue Nov 20 20:28:09 IST 2018

Reverse Range

Reverse ranges also possible in Groovy

HelloWorld.groovy

def range = 10..1

for (i in range){
 print i + " "
}

Output

10 9 8 7 6 5 4 3 2 1

Iterate over range elements

By using 'each' method (or) for-in loop you can iterate over the elements of the range.

HelloWorld.groovy

def range = 10..1

for (element in range){
 print element + " "
}

println ""

range.each{ element -> print element + " "}

Output

10 9 8 7 6 5 4 3 2 1

You can even use, ranges in switch case like below.

HelloWorld.groovy

int marks = 65

switch(marks){
 case 0..34 : println "failed"; break
 case 35..59 : println "Second Class"; break
 case 60..69 : println "First Class"; break
 case 70..100 : println "Distinction"; break
 default : println "invalid value"
}

Output

First Class

You can even grep the range of elements from a collection.

HelloWorld.groovy

def primes = [2, 3, 5, 7, 11, 13, 17, 23, 29, 31, 37, 41, 43, 47]

def range = 15..40

def primesBeetween = primes.grep(range)

println primesBeetween

Output

[17, 23, 29, 31, 37]

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Programming for beginners

Thursday, 17 January 2019

Groovy: Specify ranges to custom types

Groovy: Range (..) operator