To assure that the Key
class works correctly as a key in a java.util.HashMap
, two methods should be overridden: hashCode()
and equals(Object o)
.
A. public int hashCode()
- This method needs to be overridden to provide a unique hash code for each Key
object. The HashMap
uses the hash code to determine the bucket location for storing and retrieving objects.
D. public boolean equals(Object o)
- This method needs to be overridden to define the equality comparison for Key
objects. The HashMap
uses the equals()
method to check if two keys are equal or not.
Options B, C, and E are incorrect:
B. public boolean equals(Key k)
- This method is not the correct signature for the equals()
method. The equals()
method should take an Object
parameter, not a specific type.
C. public int compareTo(Object o)
- This method is not necessary for the Key
class to work as a key in a HashMap
. The compareTo()
method is used for sorting objects and is not relevant to the HashMap
implementation.
E. public boolean compareTo(Key k)
- This method is not the correct signature for the compareTo()
method. The compareTo()
method should take an Object
parameter, not a specific type.
Therefore, the correct answer is options A and D.