Groovy - Spaceship Operator

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Spaceship operator is used to compare objects and is denoted by <=> operator. Spaceship operator works perfectly for objects which implement Comparable Interface correctly.

Spaceship Operator Functionality

obj1 <=> obj2

Here obj1 and obj2 are compared and spaceship operator returns.

• -1 − if obj1 is less than obj2

• 0 − if obj1 is same as obj2

• 1 − if obj1 is more than obj2

Usage of Spaceship Operator

We can use spaceship operator to compare numbers, strings, dates and custom objects which implements Comparable interface. Let's compare each type using spaceship operator in below examples.

Example - Compare Numbers

Example.groovy

class Example { 
   static void main(String[] args) { 
      // prints 1 as 5 is greater than 1
      println 5 <=> 1  
      // prints 0 as 3 is equal to 3
      println 3 <=> 3   
      // prints -1 as 2 is less than 7
      println 2 <=> 7   
   } 
} 

Output

When we run the above program, we will get the following result.

1
0
-1

Example - Compare Strings

Example.groovy

class Example { 
   static void main(String[] args) { 
      // prints 1 as apple comes before banana lexicographically
      println "apple" <=> "banana"  
      // prints 0 as as cat is same as cat
      println "cat" <=> "cat"   
      // prints -1 as as zebar comes after horse lexicographically
      println "zebra" <=> "horse"   
   } 
} 

Output

When we run the above program, we will get the following result.

1
0
-1

Example - Compare Dates

Example.groovy

class Example { 
   static void main(String[] args) { 
      def date1 = new Date(125, 0, 1) // January 1, 2025
      def date2 = new Date(125, 0, 15) // January 15, 2025    
      def date3 = new Date(125, 0, 1) // January 1, 2025   
   
      // prints -1 as date1 comes before date2
      println date1 <=> date2
      // prints 0 as as date1 is same as date3
      println date1 <=> date3
      // prints 1 as as date2 comes after date1
      println date2 <=> date1   
   } 
} 

Output

When we run the above program, we will get the following result.

-1
0
1

Example - Compare Custom Objects

Example.groovy

class Example { 
   static void main(String[] args) { 
      def v101 = new Version(1, 0, 1)
      def v102 = new Version(1, 0, 2)
   
      // prints -1 as v101 comes before v102
      println v101 <=> v102
      // prints 0 as as v101 is same as new Version(1, 0, 1)
      println v101 <=> new Version(1, 0, 1)
      // prints 1 as as v102 comes after v101
      println v102 <=> v101   
   } 
} 
class Version implements Comparable<Version> {
   int major;
   int minor;
   int patch;

   Version(int major, int minor, int patch) {
      this.major = major;
      this.minor = minor;
      this.patch = patch;
   }

   @Override
   int compareTo(Version other) {
      if (major != other.major) {
         return major <=> other.major; 
      }
      if (minor != other.minor) {
         return minor <=> other.minor;
      }
      return patch <=> other.patch;
   }
   
   Version next() {
      return new Version(major, minor, patch + 1);
   }   
   
   String toString() {
      return "${major}.${minor}.${patch}";
   }
}

Output

When we run the above program, we will get the following result.

-1
0
1