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.

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.

GroovyArrayDeclaration.groovy

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.

GroovyArrayAccessItem.groovy

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.

GroovyAddItemException.groovy

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.

GroovyArrayLength.groovy

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.

GroovyArrayMinMax.groovy

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.

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