In hash base elements (hash map) when you make the equal check for two objects first their hashcode method is get called, if it return same value for both then only equals method is get called.
#OVERRIDING EQUALS METHOD MAP CODE#
2) Right click + insert code + Generate equals () and hashCode (). Override equals () and hashCode () In Eclipse and Netbeans In Netbeans 1) Write your Class. The reason behind is that in hash base elements two objects are equal if their equals method return true and their hashcode method return same integer value. The various methods to override hashCode () method are as follows. Yes it's correct when you override equals method you have to override hashcode method as well. Hope it was clear what is the disadvantage of overriding equals and not hashcode and vice versa?
Then when you call myMap.put(second,someOtherValue) it should replace first with second as per the Map Documentation because they are equal (according to the business requirement).īut the problem is that equals was not redefined, so when the map hashes second and iterates through the bucket looking if there is an object k such that second.equals(k) is true it won't find any as second.equals(first) will be false. If you only override hashCode then when you call myMap.put(first,someValue) it takes first, calculates its hashCode and stores it in a given bucket. So, although they are equal, as they don't hash to the same bucket, the map can't realize it and both of them stay in the map.Īlthough it is not necessary to override equals() if we override hashCode(), let's see what would happen in this particular case where we know that two objects of M圜lass are equal if their importantField is equal but we do not override equals(). If only equals is overriden, then when you call myMap.put(first,someValue) first will hash to some bucket and when you call myMap.put(second,someOtherValue) it will hash to some other bucket (as they have a different hashCode). Note: When you override the any super class method in scala. Therefore, the class may violate the invariant that equal objects must have equal hashcodes. M圜lass second = new M圜lass("a","second") Employee Class (Emploee.scala) The below Employee class, which is overriding the equals () method and returning boolean value based on the conditions. This class defines a hashCode() method but not an equals() method. Imagine you have this M圜lass first = new M圜lass("a","first")
Say we have a class like this and that two objects of M圜lass are equal if their importantField is equal (with hashCode() and equals() generated by eclipse) public class M圜lass else if (!importantField.equals(other.importantField)) Let's try to understand it with an example of what would happen if we override equals() without overriding hashCode() and attempt to use a Map. Failure to do so will result in a violation of the general contract for Object.hashCode(), which will prevent your class from functioning properly in conjunction with all hash-based collections, including HashMap, HashSet, and Hashtable. You must override hashCode() in every class that overrides equals(). Why do I need to override the equals and hashCode methods in Java?
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