Can some explain this code to me please?

Question

class Animal {
String name;
Animal(String n) {
name = n;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((name == null) ? 0 : name.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
Ani

Answer 1

Yes, hashCode belongs to object class, and equals too. Is recommended to overwrite them if you gonna use it.

hasCode is used to generate key values for hash data structures, like a hash table. It must return different values for each object with different attribute values.

equals is used to know if two objects have the same attribute values. If you use '==', it just compare object references.

Hope this make sense for you. ;)

Answer 2

The explanation is added as comments. I hope it can be at least a little bit useful:

class Animal {

String name;

/*
simple constructor ~ assigning of name value (object of String)
*/
Animal(String n) {
name = n;
}

@Override
public int hashCode() {
final int prime = 31;
int result = 1;
/*
basically if the name is null (no object of string class is assigned to name) it counts result as :
prime*result (because result is 1 it can even be just prime)

is the name is not null it counts hash (result) as sum of prime*result + name.hashCode () (hashCode of name added with prime)

here the ternary operator is used instead of if statement (https://en.m.wikipedia.org/wiki/%3F:)

*/
result = prime * result + ((name == null) ? 0 : name.hashCode());
return result;
}

/*

here the function returns true, when object to be compared is the same ( it is the same instance of class)

when the object to compare is null (actually nothing) or is not of the same class, it returns false

( there is the case, when the object is of same class but not the exactly same instance, which is not considered )

*/
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;

Answer 3

is the name.Hashcode() a built in function belong to the object class?

Answer 4

thanks guys