What happens if you override equals but not hashCode?

31 Answers. You must override hashCode() in every class that overrides equals(). 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.

Is it necessary to override hashCode and equals method?

If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result. It is not required that if two objects are unequal according to the equals(java. lang.

Can hashCode method be overridden?

Whenever you override equals method, hashcode should be overridden to be in compliance with equals hashcode contract. 2. hashCode() is declared in Object class and return type of hashcode method is int and not long.

Which class does override the equals () and hashCode () methods?

The Team class overrides only equals(), but it still implicitly uses the default implementation of hashCode() as defined in the Object class. And this returns a different hashCode() for every instance of the class.

What happens if you don’t override?

Put differently: If you don’t override equals any two objects will be considered non-equal. Since Object. hashCode ensures that all objects are distributed as evenly as possible in a hash based collection Object. hashCode is optimal, and overriding it with anything else will worsen the performance.

What is the importance of hashCode () and equals () methods?

The equals() and hashcode() are the two important methods provided by the Object class for comparing objects. Since the Object class is the parent class for all Java objects, hence all objects inherit the default implementation of these two methods.

What happens if we override hashCode only?

Only Override HashCode, Use the default Equals: Only the references to the same object will return true. In other words, those objects you expected to be equal will not be equal by calling the equals method.

What is the relation between hashCode and equals?

The hashCode() method should return the same integer value for the same object for each calling of this method unless the value stored in the object is modified. If two objects are equal(according to equals() method) then the hashCode() method should return the same integer value for both the objects.

What happens if hashCode () method always return same value?

When two key return same hashcode, they end up in the same bucket. Now, in order to find the correct value, you used keys. equals() method to compare with key stored in each Entry of linked list there. You can also see here for full list of interview question on Java HashMap.

How to override equals and hashCode method in Java?

Since HashMap and Hashtable in Java relies on equals () and hashCode () method for comparing keys and values. Java provides following rules to override equals method Java: Reflexive: Object must be equal to itself. Symmetric: If a.equals (b) is true then b.equals (a) must be true.

When do you call hashCode on two objects?

If two objects are equal according to the equals (Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.

Do you have to use the same field in equals and hashCode?

equals and hashCode must depend on the same set of significant fields. You must use the same set of fields in both of these methods. You are not required to use all fields. For example, a calculated field that depends on others should very likely be omitted from equals and hashCode.

Can you generate equals hashCode and compareTo in Eclipse?

Though modern IDE like Eclipse, IntelliJ or Netbeans allows you to generate equals, hashCode and compareTo methods for your value classes, it’s equally important, you know how to do that by hand.