What Method should the Key Class of Hashmap Override

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The methods to override are equals() and hashCode().

For the HashMap class in Java, the key class should override the hashCode() and equals() methods. These methods are crucial for proper functioning of the HashMap as they determine how keys are stored and retrieved in the underlying data structure.

Here’s a brief explanation of each method:

  1. hashCode(): This method returns a hash code value for the object. The hash code is used by the HashMap to quickly locate the bucket where the corresponding key-value pair is stored. It’s important that if two objects are considered equal (according to the equals() method), their hash codes must be the same.
  2. equals(Object obj): This method is used to compare two objects for equality. In the context of HashMap, it is used to check if two keys are equal. If the equals() method returns true for two keys, then their corresponding values can be retrieved or updated interchangeably.

Here’s an example of how a custom key class might look like:

java
public class CustomKey {
private String keyData;// Constructors, getters, setters, etc.

@Override
public int hashCode() {
// Custom logic to generate hash code
return Objects.hash(keyData);
}

@Override
public boolean equals(Object obj) {
// Custom logic to compare two keys for equality
if (this == obj) return true;
if (obj == null || getClass() != obj.getClass()) return false;
CustomKey otherKey = (CustomKey) obj;
return Objects.equals(keyData, otherKey.keyData);
}
}

By providing a proper implementation of hashCode() and equals() in the key class, you ensure the correct behavior of HashMap when dealing with custom keys.