Interview: hashcode() and equals()

Q：hashCode() What's the usage? ？
hashCode() yes Object Class , Returns the hash value of the object , Used to determine the index position of the object in the hash table .
Q：hashCode() How to use it? ？
When inserting data into a hash table , The hash value of the object will be calculated first to determine the insertion location , If the position is without elements , Then the direct insertion succeeds . If there are elements , Hash table will utilize equals() Method to compare with the element at that location . If the element to be inserted is related to equals() return true, So insert failed , If you return false, Then the hash table will hash it to other locations or use the zipper method to add it .
Q： Why? java To provide these two methods ？
Because of the hashcode(), It is more efficient to judge whether the elements are equal .
Q： Why rewrite equals() To rewrite hashcode()？
Guarantee equals() return True when hashcode() Also equal . If you do not override , There may be a equals() return true, But two objects hashcode() Unequal .