Java HashSet contains returns false even with equals () and hashCode () overridden
I am initializing the HashSet like this:
private HashSet<Rule> ruleTable = new HashSet<Rule>();
Methods equals()
and hashCode()
my object TcpRule
(abstract class subclass Rule
) as follows:
@Override
public int hashCode() {
// Ignore source Port for now
return (this.getSrcPool() + ":" + this.getDstPool() + ":" + this.getProtocol() + ":" + this.dstTcp).hashCode();
}
@Override
public boolean equals(Object obj) {
if (!(obj instanceof TcpRule))
return false;
if (obj == this)
return true;
TcpRule r = (TcpRule) obj;
return (this.getSrcPool().equals(r.getSrcPool()) && this.getDstPool().equals(r.getDstPool()) && this.getProtocol().equals(r.getProtocol()) && this.getSrcTcp() == r.getSrcTcp() && this.getDstTcp() == r.getDstTcp());
}
I even wrote a simple unit test that doesn't give any error:
@Test
public void equalsTest() {
Pool srcPool = new Pool("PROXY");
Pool dstPool = new Pool("WEB");
int srcTcp = 54321;
int dstTcp = 80;
TcpRule r1 = new TcpRule(srcPool, dstPool, srcTcp, dstTcp);
TcpRule r2 = r1;
assert r1.equals(r2);
TcpRule r3 = new TcpRule(srcPool, dstPool, srcTcp, dstTcp);
TcpRule r4 = new TcpRule(srcPool, dstPool, srcTcp, dstTcp);
assert r3.equals(r4);
}
@Test
public void hashCodeTest() {
Pool srcPool = new Pool("PROXY");
Pool dstPool = new Pool("WEB");
int srcTcp = 54321;
int dstTcp = 80;
TcpRule r1 = new TcpRule(srcPool, dstPool, srcTcp, dstTcp);
TcpRule r2 = new TcpRule(srcPool, dstPool, srcTcp, dstTcp);
assert r1.hashCode() == r2.hashCode();
HashSet<Rule> rules = new HashSet<Rule>();
rules.add(r1);
assert rules.contains(r1);
assert rules.contains(r2);
}
In my application, I have a method add()
where I just add an object Rule
to HashSet
:
@Override
public void add(Rule rule) {
ruleTable.add(rule);
}
In another method, I check if a rule exists in HashSet
:
@Override
public boolean isPermittedTcp(IpAddress sourceAddress, IpAddress destinationAddress, short srcTcp, short dstTcp) {
Pool sourcePool = poolService.getPool(new Host(sourceAddress));
Pool destinationPool = poolService.getPool(new Host(destinationAddress));
Rule r = new TcpRule(sourcePool, destinationPool, srcTcp, dstTcp);
log.info("Checking: " + r.toString());
log.info("Hash-Code: " + r.hashCode());
log.info("Hashes in ruleTable:");
for(Rule rT : ruleTable) {
log.info("" + rT.hashCode());
}
if(ruleTable.contains(r)) {
log.info("Hash found!");
} else {
log.info("Hash not found!");
}
return ruleTable.contains(r);
}
The log messages show that the hash of the object Rule
( r.hashCode()
) is equal -1313430269
, and that one hash in HashSet
( rT.hashCode()
in the loop) also -1313430269
. But it ruleTable.contains(r)
always returns false
. What am I doing wrong?
I found similar questions on StackOverflow, but they mostly involve methods equals()
or methods hashCode()
that have not been (correctly) overridden. I think I have implemented these two methods correctly.
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You have an additional condition in equals this.getSrcTcp () == r.getSrcTcp () that is not part of the hashcode - it might be a problem, the hashcode is the same but false. Check if this field is different from the compared values.
Despite the comments, I think the reason this doesn't work is because the equals and hashCode implementations don't share the same fields.
Code to simulate the problem:
import java.util.HashSet;
/**
* @author u332046
*
*/
public class HashCodeCollisionTest {
public static class KeyDemo {
String id;
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ((id == null) ? 0 : id.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;
KeyDemo other = (KeyDemo) obj;
if (id == null) {
if (other.id != null)
return false;
} else if (!id.equals(other.id))
return false;
return true;*/
return false;
}
public KeyDemo(String id) {
super();
this.id = id;
}
}
static HashSet<KeyDemo> set = new HashSet<>();
public static void main(String[] args) {
set.add(new KeyDemo("hi"));
set.add(new KeyDemo("hello"));
System.out.println(set.contains(new KeyDemo("hi")));
}
}
Will print false
. Uncomment the equality code and typetrue
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