Can hashcode collision affect equals in Java? -


the hashcode() contract allows different objects have same hash code. document:

it not required if 2 objects unequal according equals(java.lang.object) method, calling hashcode method on each of 2 objects must produce distinct integer results.

at same time, in eclipse, if use function source->generate hashcode() , equals, thing this:

package test1;  public class j1 {     private int a;     private int b;      @override     public int hashcode() {         final int prime = 31;         int result = 1;         result = prime * result + a;         result = prime * result + b;         return result;     }      @override     public boolean equals(object obj) {         //compare hashcode         if (this == obj)             return true;         if (obj == null)             return false;         if (getclass() != obj.getclass())             return false;         j1 other = (j1) obj;         if (a != other.a)             return false;         if (b != other.b)             return false;         return true;     } }

in function equals(), first compare hashcode of this , obj, if have same hashcode, equals() returns true. document says 2 different objects may have different hashcode, affect correctness of equals(). can't figure out problem.

in function equals(), first compare hashcode of , obj, if have same hashcode, equals() returns true.

no, if (this == obj) does not compare hash code of 2 objects. checks whether this , obj referring same object, in case must equal (since object should equal itself), following logic of equals doesn't need executed in case.

on other hand, if this != obj, this , obj referring different objects, may still equal each other, depending on logic of equals. if logic of equals returns true, contract requires must have same hashcode().


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