Why we need @lazy property in Groovy, what's its advantages?

Question

One of the most confusing concepts when I've learnt Groovy is : lazy property. Can't find similarly anything from C/C++ Does anyone know why we need this stuff and how we can live without it, or alternative way to do. Appreciate any help :)

Answer 1

@Lazy annotation in groovy is normally used for a field within an object which is time or memory expensive to create. With this annotation the field value in the object is not calculated when you create an instance of the object, instead of is calculated when you make the first call to get it.

So i.e you create an instance of an object but you don't get the field with @Lazy annotation the field value is never calculated so you're saving time execution and memory resources. Look on the code sample (the sample has nonsense but I hope that can help to understand the explanation):

// without lazy annotation with this code token.length is calculated even
// is not used
class sample{
    String token
    Integer tokenSize = { token?.length() }()
}

def obj = new sample()
obj.token = 'aaaaaaaaaaaaaaaaaaaaaaaaaaaa'

// with Lazy annotation tokenSize is not calculated because the code
// is not getting the field.
class sample{
    String token
    @Lazy tokenSize = { token?.length() }()
}

def obj = new sample()
obj.token = 'aaaaaaaaaaaaaaaaaaaaaaaaaaaa'

Hope this helps,