What is the difference between hashCode and equals method in Java?

What is hashCode and equals method in Java?

A hashcode is an integer value associated with every object in Java, facilitating the hashing in hash tables. … The hashcode() method returns the same hash value when called on two objects, which are equal according to the equals() method. And if the objects are unequal, it usually returns different hash values.

What is relation between hashCode and equals method?

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 is equals () and hashCode () contract in Java?

Contract between hashCode() and equals() … 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.

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What happens if we don’t override hashCode method?

If you don’t override hashcode() then the default implementation in Object class will be used by collections. This implementation gives different values for different objects, even if they are equal according to the equals() method.

What is hashCode used for?

hashCode() is used for bucketing in Hash implementations like HashMap , HashTable , HashSet , etc. The value received from hashCode() is used as the bucket number for storing elements of the set/map. This bucket number is the address of the element inside the set/map.

Can 2 objects have same hashCode?

It is perfectly legal for two objects to have the same hashcode. If two objects are equal (using the equals() method) then they have the same hashcode.

Is equal method in Java?

Java String equals() Method

The equals() method compares two strings, and returns true if the strings are equal, and false if not. Tip: Use the compareTo() method to compare two strings lexicographically.

What is hashCode and how it works?

Simply put, hashCode() returns an integer value, generated by a hashing algorithm. Objects that are equal (according to their equals()) must return the same hash code. Different objects do not need to return different hash codes.

How do you write a good hashCode method?

When implementing hashCode :

  1. Use a the same fields that are used in equals (or a subset thereof).
  2. Better not include mutable fields.
  3. Consider not calling hashCode on collections.
  4. Use a common algorithm unless patterns in input data counteract them.

What happens if we override equals method and override hashCode method?

Overriding only equals() method without overriding hashCode() causes the two equal instances to have unequal hash codes, which violates the hashCode contract (mentioned in Javadoc) that clearly says, if two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two

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