HashMap containsKey() returns false although hashCode() and equals() are true
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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
edited Mar 26 at 10:12
Eran
292k37481564
asked Mar 26 at 10:01
gutenmorgenuhugutenmorgenuhu
1,69911229
|
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
edited Mar 26 at 10:12
Eran
292k37481564
asked Mar 26 at 10:01
gutenmorgenuhugutenmorgenuhu
1,69911229
13
So the keys are instances ofVertex, not ofString? But the key you are checking for is aString. AStringwill never be equal to anything but anotherString.
– khelwood
Mar 26 at 10:03
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
Mar 26 at 10:05
9
toString()is irrelevant, and even if yourVertexinstance claims to be equal to aString, theStringinstance will not say it is equal to aVertex.
– khelwood
Mar 26 at 10:06
@khelwood unless in a very alternative implementation of an equals method :)
– Stultuske
Mar 26 at 10:08
1
Possible duplicate of What issues should be considered when overriding equals and hashCode in Java?
– Lino
Mar 26 at 10:10
|
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
edited Mar 26 at 10:12
Eran
292k37481564
asked Mar 26 at 10:01
gutenmorgenuhugutenmorgenuhu
1,69911229
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 Mar 26 at 10:12
Eran
292k37481564
asked Mar 26 at 10:01
gutenmorgenuhugutenmorgenuhu
1,69911229
edited Mar 26 at 10:12
Eran
292k37481564
asked Mar 26 at 10:01
gutenmorgenuhugutenmorgenuhu
1,69911229
edited Mar 26 at 10:12
Eran
292k37481564
edited Mar 26 at 10:12
Eran
292k37481564
edited Mar 26 at 10:12
Eran
292k37481564
292k37481564
asked Mar 26 at 10:01
gutenmorgenuhugutenmorgenuhu
1,69911229
asked Mar 26 at 10:01
gutenmorgenuhugutenmorgenuhu
1,69911229
asked Mar 26 at 10:01
gutenmorgenuhugutenmorgenuhu
1,69911229
1,69911229
13
So the keys are instances ofVertex, not ofString? But the key you are checking for is aString. AStringwill never be equal to anything but anotherString.
– khelwood
Mar 26 at 10:03
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
Mar 26 at 10:05
9
toString()is irrelevant, and even if yourVertexinstance claims to be equal to aString, theStringinstance will not say it is equal to aVertex.
– khelwood
Mar 26 at 10:06
@khelwood unless in a very alternative implementation of an equals method :)
– Stultuske
Mar 26 at 10:08
1
Possible duplicate of What issues should be considered when overriding equals and hashCode in Java?
– Lino
Mar 26 at 10:10
|
show 1 more comment
13
So the keys are instances ofVertex, not ofString? But the key you are checking for is aString. AStringwill never be equal to anything but anotherString.
– khelwood
Mar 26 at 10:03
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
Mar 26 at 10:05
9
toString()is irrelevant, and even if yourVertexinstance claims to be equal to aString, theStringinstance will not say it is equal to aVertex.
– khelwood
Mar 26 at 10:06
@khelwood unless in a very alternative implementation of an equals method :)
– Stultuske
Mar 26 at 10:08
1
Possible duplicate of What issues should be considered when overriding equals and hashCode in Java?
– Lino
Mar 26 at 10:10
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
Mar 26 at 10:03
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
Mar 26 at 10:03
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
Mar 26 at 10:05
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
Mar 26 at 10:05
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
Mar 26 at 10:06
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
Mar 26 at 10:06
@khelwood unless in a very alternative implementation of an equals method :)
– Stultuske
Mar 26 at 10:08
@khelwood unless in a very alternative implementation of an equals method :)
– Stultuske
Mar 26 at 10:08
1
1
Possible duplicate of What issues should be considered when overriding equals and hashCode in Java?
– Lino
Mar 26 at 10:10
Possible duplicate of What issues should be considered when overriding equals and hashCode in Java?
– Lino
Mar 26 at 10:10
|
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.
answered Mar 26 at 10:05
EranEran
292k37481564
add a comment |
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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.
answered Mar 26 at 10:05
EranEran
292k37481564
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.
answered Mar 26 at 10:05
EranEran
292k37481564
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.
answered Mar 26 at 10:05
EranEran
292k37481564
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.
answered Mar 26 at 10:05
EranEran
292k37481564
edited Mar 26 at 10:24
answered Mar 26 at 10:05
EranEran
292k37481564
answered Mar 26 at 10:05
EranEran
292k37481564
answered Mar 26 at 10:05
EranEran
292k37481564
292k37481564
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. AStringwill never be equal to anything but anotherString.– khelwood
Mar 26 at 10:03
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
Mar 26 at 10:05
9
toString()is irrelevant, and even if yourVertexinstance claims to be equal to aString, theStringinstance will not say it is equal to aVertex.– khelwood
Mar 26 at 10:06
@khelwood unless in a very alternative implementation of an equals method :)
– Stultuske
Mar 26 at 10:08
1
Possible duplicate of What issues should be considered when overriding equals and hashCode in Java?
– Lino
Mar 26 at 10:10