Generating Proper equals() and hashCode() by @Equiv Annotations

We've released a small Groovy library named "kobo-commons" which has some convenience features for Groovy programming.

• http://github.com/kobo/kobo-commons

@Equiv annotation is one of the features.

If you annotate fields by @Equiv annotations, you can dynamically generate
proper equals() and hashCode() using specified fields.


If you wrote the following groovy code:

view plainprint?

1. class Sample {  
2.     @Equiv  
3.     String name  
4.   
5.     @Equiv  
6.     String value  
7.   
8.     String ignored  
9. }  

class Sample {
    @Equiv
    String name

    @Equiv
    String value

    String ignored
}

then you could use equals method and hashCode method:

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1. def s1 = new Sample(name:'John', value:'Good', ignored:'Garbage')  
2. def s2 = new Sample(name:'John', value:'Good', ignored:'Gold')  
3. def s3 = new Sample(name:'John', value:'Bad',  ignored:'Garbage')  
4. def s4 = new Sample(name:'Mike', value:'Good', ignored:'Garbage')  
5.       
6. assert s1 == s1  
7. assert s1 == s2  
8. assert s1 != s3  
9. assert s1 != s4  
10.       
11. assert s1.hashCode() == s1.hashCode()  
12. assert s1.hashCode() == s2.hashCode()  
13. assert s1.hashCode() != s3.hashCode()  
14. assert s1.hashCode() != s4.hashCode()  

def s1 = new Sample(name:'John', value:'Good', ignored:'Garbage')
def s2 = new Sample(name:'John', value:'Good', ignored:'Gold')
def s3 = new Sample(name:'John', value:'Bad',  ignored:'Garbage')
def s4 = new Sample(name:'Mike', value:'Good', ignored:'Garbage')
    
assert s1 == s1
assert s1 == s2
assert s1 != s3
assert s1 != s4
    
assert s1.hashCode() == s1.hashCode()
assert s1.hashCode() == s2.hashCode()
assert s1.hashCode() != s3.hashCode()
assert s1.hashCode() != s4.hashCode()

I think it's useful for entities, etc. You can keep your classes very simple.