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About Huseyin Babal

Huseyin Babal
Huseyin Babal has deep experience in Full Stack Development since 2007. He is mainly developing applications with JAVA, Spring, PHP, NodeJS, AngularJS. He is also interested in DevOps Engineering since 2013 and using AWS, Heroku for Cloud deployment and playing with Docker and Consul for implementing infinite scalable systems. He likes to share his experience in public conferences and perform advanced workshops about Full Stack Development and Devops. He is the author of NodeJS in Action course in Udemy.

Groovy Array Example

1. Introduction

In previous tutorials, we have mentioned about Groovy List and provided lots of examples. In this tutorial, I will show you how to use Groovy arrays. Even if array and list seems to be same, they have differences in common. For example, arrays have fixed size while lists have dynamic size that means you can add item as much as you can after initialization of the list. If you try to add item to array with a size bigger than initial size of the array after initialization, you will get MissingMethodException or ArrayIndexOutOfBoundsException. After some theory, let’s see some Groovy arrays in action.

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2. Array Declaration

In Groovy, you can declare array in Java style or Groovy style. Let’s have a look at following example for array declaration.


package com.javacodegeeks.groovy.array

class GroovyArrayDeclaration {

	static main(args) {
		def birds = new String[3]
		birds[0] = "Parrot"
		birds.putAt(1, "Cockatiel")
		birds[2] = "Pigeon"
		println birds // [Parrot, Cockatiel, Pigeon]
		def birdArr = ["Parrot", "Cockatiel", "Pigeon"] as String[] // You say that this is an array of Strings
		println birdArr // [Parrot, Cockatiel, Pigeon]


As you can see in the example, you can declare an array with a size, and then you can put elements in different ways in Java style. In second example, the array is directly declared with initial values. Also, it has been casted to the String that means this array has elements of type String.

3. Access Array Items

In Groovy, you can access array item by using square bracket with an index ([index]) or using getAt(index) function. Let’s have a look at following example to see what is going on.


package com.javacodegeeks.groovy.array

class GroovyArrayAccessItem {

	static main(args) {
		def birds = ["Parrot", "Cockatiel", "Pigeon"] as String[]
		println birds[0] // Parrot
		println birds[2] // Pigeon
		println birds.getAt(1) // Cockatiel
		println birds[-1] // Pigeon
		println birds[-3] // Parrot


As you may already know, it is easy to understand the case on line 09, line 10 and line 11. They are simple operations to get items on specific index. What about on line 13? Why we use negative index? It is simple, when you use negative index, it will be accessed from the end of the array with 1 based index. When you say -1 it means the first element from the end. And in same way, when you say -3, it means third element from the end.

4. Add Item Exception

As we said earlier, If you try to add items to an array with a bigger size than the fixed length, you will get an exception as in the example below.


package com.javacodegeeks.groovy.array

class GroovyAddItemException {

	static main(args) {
		def birds = ["Parrot", "Cockatiel", "Pigeon"] as String[]
		birds << "Eagle" // MissingMethodException
		birds.putAt(3, "Owl") // ArrayIndexOutOfBoundsException


On line 08, the method << belongs to list, that is why we got MissingMethodException. On line 10 we have exception due to overflow the size of the array wit a size 3.

5. Array Length

In Java, you can use size() method for the list, and length method for the arrays in order to get actual size of the object. In Groovy, it has been simplified and you can use size method for both arrays or lists. You can see simple example below.


package com.javacodegeeks.groovy.array

class GroovyArrayLength {

	static main(args) {
		def birds = ["Parrot", "Cockatiel", "Pigeon"] as String[]
		println birds.length // 3
		println birds.size() // 3


6. Array Min & Max Value

Let say that, you have array of numbers. You can easily find the minimum and maximum value by using the min() and max() functions over arrays as below.


package com.javacodegeeks.groovy.array

class GroovyArrayMinMax {

	static main(args) {
		def numbers = [32, 44, 12, 9, 100, 180]
		println numbers.max() // 180
		println numbers.min() // 9
		def birds = ["Parrot", "Cockatiel", "Pigeon"] as String[]
		println birds.max { it.size() } // Cockatiel
		println birds.min { it.size() } // Parrot


On line 09 and line 10 you can easily understand the case but, the trick on line 14 and line 15 is, the minimum and maximum value is determined by the length of the current string value. Let say that you are iterating to find minimum and maximum value, it means current value in the array.

7. Remove Item

Removing item here is not actually removing item from array. It is something like assign the array with one item removed version to another variable. Let see it in action.


package com.javacodegeeks.groovy.array

class GroovyArrayRemoveItem {

	static main(args) {
		def birds = ["Parrot", "Cockatiel", "Pigeon"] as String[]
		def birdsWithoutParrot = birds - "Parrot"
		println birds // [Parrot, Cockatiel, Pigeon]
		println birdsWithoutParrot // [Cockatiel, Pigeon]


As you can see on line 09, we are using subtracting method to remove one item and assign final version to another variable. It is not removed from the original array actually as you can see on line 11. However, you can see another array without “Parrot” on line 13.

8. Array Ordering

If you are interacting with collections, you may need to do ordering operations time to time. For example, you may want to reverse array, or sort the array items. You can see following example to see how it looks like.


package com.javacodegeeks.groovy.array

class GroovyArrayOrdering {

	static main(args) {
		def birds = ["Parrot", "Cockatiel", "Pigeon"] as String[]
		println birds.reverse() // [Pigeon, Cockatiel, Parrot]
		println birds.sort() // [Cockatiel, Parrot, Pigeon]


In above example, array is reversed and items printed on the screen in reverse way on line 09. Also, array sorted in alphabetical order by using sort() function. You can see it on line 11

9. Array Lookup

You can perform lookup operations on arrays. In following example we will reverse every item text and also we will find an item by matching a provided regex. Let’s do it.


package com.javacodegeeks.groovy.array

class GroovyArrayLookup {

	static main(args) {
		def birds = ["Parrot", "Cockatiel", "Pigeon"] as String[]
		def revertedBirds = birds.collect { it.reverse() }
		println revertedBirds // [torraP, leitakcoC, noegiP]
		def founded = birds.find { it =~ /Cockatiel/ }
		println founded // Cockatiel


On line 11, we have iterated by using collect function and reversed each item by using reverse() function. Again, it stands for the current item in the code. On line 13, we have used find function to find specific item by using regular expression.

10. Conversion

You can also convert array to list in Groovy easily. You can see following example for simple usage.


package com.javacodegeeks.groovy.array

class GroovyArrayConversion {

	static main(args) {
		def birds = ["Parrot", "Cockatiel", "Pigeon"] as String[]
		def birdList = birds.toList()
		println birdList.class.name // java.util.ArrayList
		def birdsAgain = birdList as String[]
		println birdsAgain.class.name // [Ljava.lang.String;


On line 09, we have used toList function to convert array to list. When you check the class name of birdList you will see it is instance of java.util.ArrayList. As you can guess, you can convert list to array. Check out line 13 and it is easily casted to array. You can check the class name on line 15, and you will see it is [Ljava.lang.String;

11. Conclusion

To sum up, array and list has same properties in common, but there are major differences between array and list. One of the well known difference is array has fixed size and list has dynamic size in usage. If you try to add more item bigger than the array size, you will get exception. Additionally, you can perform many operations on array like list.

You can download the full source code of the project here: GroovyArrayExample

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