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

• In Java, a HashMap uses the hashCode and equals methods to determine the index of the key-value pair and to detect duplicates.
• More specifically, the hashCodemethod is used in order to determine where the specified key will be stored. 
• Since different keys may produce the same hash value, the equals method is used, in order to determine whether the specified key actually exists in the collection or not.
• Therefore, the implementation of both methods is crucial to the accuracy and efficiency of the HashMap.