HashMap containsKey() returns false although hashCode() and equals() are true
I have a HashMap<Vertex, Integer>
called vertexIndexes
. If I iterate through it with this code:
public boolean search(String vertexName){
for (Vertex name: vertexIndexes.keySet()){
String key = name.toString();
String value = vertexIndexes.get(name).toString();
System.out.println(key + " " + value + " "+ (name.hashCode() == vertexName.hashCode()) + " " + name.equals(vertexName));
}
...
}
it produces this output:
Diessen 0 false false
Herrsching 5 false false
Schondorf 2 false false
Greifenberg 3 false false
Stegen 4 false false
Utting 1 false false
Andechs 6 false false
Fischen 7 true true
So you can see, that the Vertex Fischen
is present and the hashCode
and equals
methods work fine. But if I run
vertexIndexes.containsKey("Fischen")
it returns false
.
Why is that? I lose my mind over it.
java hashmap
|
show 1 more comment
I have a HashMap<Vertex, Integer>
called vertexIndexes
. If I iterate through it with this code:
public boolean search(String vertexName){
for (Vertex name: vertexIndexes.keySet()){
String key = name.toString();
String value = vertexIndexes.get(name).toString();
System.out.println(key + " " + value + " "+ (name.hashCode() == vertexName.hashCode()) + " " + name.equals(vertexName));
}
...
}
it produces this output:
Diessen 0 false false
Herrsching 5 false false
Schondorf 2 false false
Greifenberg 3 false false
Stegen 4 false false
Utting 1 false false
Andechs 6 false false
Fischen 7 true true
So you can see, that the Vertex Fischen
is present and the hashCode
and equals
methods work fine. But if I run
vertexIndexes.containsKey("Fischen")
it returns false
.
Why is that? I lose my mind over it.
java hashmap
13
So the keys are instances ofVertex
, not ofString
? But the key you are checking for is aString
. AString
will never be equal to anything but anotherString
.
– khelwood
2 days ago
As you can see in my output (..true true..): I implemented the toString() and equals method of Vertex to correctly compare it to a String.
– gutenmorgenuhu
2 days ago
9
toString()
is irrelevant, and even if yourVertex
instance claims to be equal to aString
, theString
instance will not say it is equal to aVertex
.
– khelwood
2 days ago
@khelwood unless in a very alternative implementation of an equals method :)
– Stultuske
2 days ago
1
Possible duplicate of What issues should be considered when overriding equals and hashCode in Java?
– Lino
2 days ago
|
show 1 more comment
I have a HashMap<Vertex, Integer>
called vertexIndexes
. If I iterate through it with this code:
public boolean search(String vertexName){
for (Vertex name: vertexIndexes.keySet()){
String key = name.toString();
String value = vertexIndexes.get(name).toString();
System.out.println(key + " " + value + " "+ (name.hashCode() == vertexName.hashCode()) + " " + name.equals(vertexName));
}
...
}
it produces this output:
Diessen 0 false false
Herrsching 5 false false
Schondorf 2 false false
Greifenberg 3 false false
Stegen 4 false false
Utting 1 false false
Andechs 6 false false
Fischen 7 true true
So you can see, that the Vertex Fischen
is present and the hashCode
and equals
methods work fine. But if I run
vertexIndexes.containsKey("Fischen")
it returns false
.
Why is that? I lose my mind over it.
java hashmap
I have a HashMap<Vertex, Integer>
called vertexIndexes
. If I iterate through it with this code:
public boolean search(String vertexName){
for (Vertex name: vertexIndexes.keySet()){
String key = name.toString();
String value = vertexIndexes.get(name).toString();
System.out.println(key + " " + value + " "+ (name.hashCode() == vertexName.hashCode()) + " " + name.equals(vertexName));
}
...
}
it produces this output:
Diessen 0 false false
Herrsching 5 false false
Schondorf 2 false false
Greifenberg 3 false false
Stegen 4 false false
Utting 1 false false
Andechs 6 false false
Fischen 7 true true
So you can see, that the Vertex Fischen
is present and the hashCode
and equals
methods work fine. But if I run
vertexIndexes.containsKey("Fischen")
it returns false
.
Why is that? I lose my mind over it.
java hashmap
java hashmap
edited 2 days ago
Eran
290k37479563
290k37479563
asked 2 days ago
gutenmorgenuhugutenmorgenuhu
1,67011229
1,67011229
13
So the keys are instances ofVertex
, not ofString
? But the key you are checking for is aString
. AString
will never be equal to anything but anotherString
.
– khelwood
2 days ago
As you can see in my output (..true true..): I implemented the toString() and equals method of Vertex to correctly compare it to a String.
– gutenmorgenuhu
2 days ago
9
toString()
is irrelevant, and even if yourVertex
instance claims to be equal to aString
, theString
instance will not say it is equal to aVertex
.
– khelwood
2 days ago
@khelwood unless in a very alternative implementation of an equals method :)
– Stultuske
2 days ago
1
Possible duplicate of What issues should be considered when overriding equals and hashCode in Java?
– Lino
2 days ago
|
show 1 more comment
13
So the keys are instances ofVertex
, not ofString
? But the key you are checking for is aString
. AString
will never be equal to anything but anotherString
.
– khelwood
2 days ago
As you can see in my output (..true true..): I implemented the toString() and equals method of Vertex to correctly compare it to a String.
– gutenmorgenuhu
2 days ago
9
toString()
is irrelevant, and even if yourVertex
instance claims to be equal to aString
, theString
instance will not say it is equal to aVertex
.
– khelwood
2 days ago
@khelwood unless in a very alternative implementation of an equals method :)
– Stultuske
2 days ago
1
Possible duplicate of What issues should be considered when overriding equals and hashCode in Java?
– Lino
2 days ago
13
13
So the keys are instances of
Vertex
, not of String
? But the key you are checking for is a String
. A String
will never be equal to anything but another String
.– khelwood
2 days ago
So the keys are instances of
Vertex
, not of String
? But the key you are checking for is a String
. A String
will never be equal to anything but another String
.– khelwood
2 days ago
As you can see in my output (..true true..): I implemented the toString() and equals method of Vertex to correctly compare it to a String.
– gutenmorgenuhu
2 days ago
As you can see in my output (..true true..): I implemented the toString() and equals method of Vertex to correctly compare it to a String.
– gutenmorgenuhu
2 days ago
9
9
toString()
is irrelevant, and even if your Vertex
instance claims to be equal to a String
, the String
instance will not say it is equal to a Vertex
.– khelwood
2 days ago
toString()
is irrelevant, and even if your Vertex
instance claims to be equal to a String
, the String
instance will not say it is equal to a Vertex
.– khelwood
2 days ago
@khelwood unless in a very alternative implementation of an equals method :)
– Stultuske
2 days ago
@khelwood unless in a very alternative implementation of an equals method :)
– Stultuske
2 days ago
1
1
Possible duplicate of What issues should be considered when overriding equals and hashCode in Java?
– Lino
2 days ago
Possible duplicate of What issues should be considered when overriding equals and hashCode in Java?
– Lino
2 days ago
|
show 1 more comment
1 Answer
1
active
oldest
votes
name.equals(vertexName)
compares a Vertex
to a String
. While your Vertex
class equals
method might return true
when you pass a String
to it, String
's equals
will never return true
when you pass a Vertex
to it.
HashMap
probably tests whether vertexName.equals(name)
, which returns false
.
Change
vertexIndexes.containsKey("Fischen")
to
vertexIndexes.containsKey(new Vertex("Fischen"))
or change the key of your Map
to String
.
BTW, you could have avoided that issue in the first place if you followed the contract of the equals
method that appears in the Javadoc of the Object
class:
• It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
Your equals
implementation is not symmetric.
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
name.equals(vertexName)
compares a Vertex
to a String
. While your Vertex
class equals
method might return true
when you pass a String
to it, String
's equals
will never return true
when you pass a Vertex
to it.
HashMap
probably tests whether vertexName.equals(name)
, which returns false
.
Change
vertexIndexes.containsKey("Fischen")
to
vertexIndexes.containsKey(new Vertex("Fischen"))
or change the key of your Map
to String
.
BTW, you could have avoided that issue in the first place if you followed the contract of the equals
method that appears in the Javadoc of the Object
class:
• It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
Your equals
implementation is not symmetric.
add a comment |
name.equals(vertexName)
compares a Vertex
to a String
. While your Vertex
class equals
method might return true
when you pass a String
to it, String
's equals
will never return true
when you pass a Vertex
to it.
HashMap
probably tests whether vertexName.equals(name)
, which returns false
.
Change
vertexIndexes.containsKey("Fischen")
to
vertexIndexes.containsKey(new Vertex("Fischen"))
or change the key of your Map
to String
.
BTW, you could have avoided that issue in the first place if you followed the contract of the equals
method that appears in the Javadoc of the Object
class:
• It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
Your equals
implementation is not symmetric.
add a comment |
name.equals(vertexName)
compares a Vertex
to a String
. While your Vertex
class equals
method might return true
when you pass a String
to it, String
's equals
will never return true
when you pass a Vertex
to it.
HashMap
probably tests whether vertexName.equals(name)
, which returns false
.
Change
vertexIndexes.containsKey("Fischen")
to
vertexIndexes.containsKey(new Vertex("Fischen"))
or change the key of your Map
to String
.
BTW, you could have avoided that issue in the first place if you followed the contract of the equals
method that appears in the Javadoc of the Object
class:
• It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
Your equals
implementation is not symmetric.
name.equals(vertexName)
compares a Vertex
to a String
. While your Vertex
class equals
method might return true
when you pass a String
to it, String
's equals
will never return true
when you pass a Vertex
to it.
HashMap
probably tests whether vertexName.equals(name)
, which returns false
.
Change
vertexIndexes.containsKey("Fischen")
to
vertexIndexes.containsKey(new Vertex("Fischen"))
or change the key of your Map
to String
.
BTW, you could have avoided that issue in the first place if you followed the contract of the equals
method that appears in the Javadoc of the Object
class:
• It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
Your equals
implementation is not symmetric.
edited 2 days ago
answered 2 days ago
EranEran
290k37479563
290k37479563
add a comment |
add a comment |
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13
So the keys are instances of
Vertex
, not ofString
? But the key you are checking for is aString
. AString
will never be equal to anything but anotherString
.– khelwood
2 days ago
As you can see in my output (..true true..): I implemented the toString() and equals method of Vertex to correctly compare it to a String.
– gutenmorgenuhu
2 days ago
9
toString()
is irrelevant, and even if yourVertex
instance claims to be equal to aString
, theString
instance will not say it is equal to aVertex
.– khelwood
2 days ago
@khelwood unless in a very alternative implementation of an equals method :)
– Stultuske
2 days ago
1
Possible duplicate of What issues should be considered when overriding equals and hashCode in Java?
– Lino
2 days ago