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equals and hashcode

 
Ranch Hand
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Hi
This is a question from PGJC exam.
class ValuePair {
public int a, b;
public boolean equals(Object other) {
try {
ValuePair o = (ValuePair) other;
return (a == o.a && b == o.b)
|| (a == o.b && b == o.a);
} catch (ClassCastException cce) {
return false;
}
}
public int hashCode() {
// Provide implementation here.
}
}
1.return 0
2. return a
3. return a+b
4.return a-b;
5. return a^b
6. return (a16)|b
I selected the options 3,4,5 but not sure.
-Sanjana
 
Greenhorn
Posts: 3
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I believe 1, 3, 5 are the options. Not quite sure about 6. If it is a | b then it should be the answer.
 
sanjana narayanan
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Hi Sam Chen,
why is that a-b cannot be one of the option. Any reasons?
-Sanjana
 
Wanderer
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Sam is correct that 1, 3, and 5 are the answers. 6 is nonsense as written - surely PGJC wrote something else here?
why is that a-b cannot be one of the option. Any reasons?
Yes. Consider two objects:
Given the definition of equals(), these two objects are equal. Therefore, their hashCode() methods must return the same values. But they don't. Answers 2 and 4 are incorrect because they would both return unequal hash codes for equal objects.
 
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