Question

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How is hashCode() calculated in Java

I found there’s no implementation in hashCode(） method of root class Object in Java:

public native int hashCode(); 

If I have an Object a and an Object b, how can I know the a.hashCode() and b.hashCode() value without using System.out.println()? Just by the hashCode implementation.

I have try to new two ArrayList objects and to my big surprise the hashCode() values are the same: both of them are 1.

Answer 1

hashCode is a native method which means that a system library is called internally. See Java Native Interface for more details.

There is a question on SO Why hashCode() and getClass() are native methods? Might be interesting for you.