Correctly implement hashcode for matrix java
0
I have a Java class containing a 2D int array. I want to implement the hashCode() method so that different objects can be compared using their attributes and not reference. This is what I tried:
public int hashCode() {
int hash = 0;
for(int i=0; i<getMatrix().length; i++) {
hash =+ Arrays.hashCode(getMatrix()[i]);
}
return hash;
}
I also tried using deepHashCode() but didn't work. My problem is that when the get() method of a HashMap object is used, even though both the object have the same matrix, the get() method does not work properly.
EDIT:
Implementation of equals method
public boolean equals(Object o) {
boolean sameBoard = false;
if(o != null && o instanceof Node) {
Node node = (Node) o;
int board1 = this.getMatrix();
int board2 = node.getMatrix();
return Arrays.deepEquals(board1, board2);
}
return sameBoard;
}
java
asked Nov 12 '18 at 20:45
Sebastian Ampuero MorisakiSebastian Ampuero Morisaki
929
|
show 1 more comment
0
I have a Java class containing a 2D int array. I want to implement the hashCode() method so that different objects can be compared using their attributes and not reference. This is what I tried:
public int hashCode() {
int hash = 0;
for(int i=0; i<getMatrix().length; i++) {
hash =+ Arrays.hashCode(getMatrix()[i]);
}
return hash;
}
I also tried using deepHashCode() but didn't work. My problem is that when the get() method of a HashMap object is used, even though both the object have the same matrix, the get() method does not work properly.
EDIT:
Implementation of equals method
public boolean equals(Object o) {
boolean sameBoard = false;
if(o != null && o instanceof Node) {
Node node = (Node) o;
int board1 = this.getMatrix();
int board2 = node.getMatrix();
return Arrays.deepEquals(board1, board2);
}
return sameBoard;
}
java
asked Nov 12 '18 at 20:45
Sebastian Ampuero MorisakiSebastian Ampuero Morisaki
929
1
Did you also implementequals? If so, can you also post your implementation of it as an edit to your post?
– Andrey Akhmetov
Nov 12 '18 at 20:47
@AndreyAkhmetov i posted it
– Sebastian Ampuero Morisaki
Nov 12 '18 at 20:51
2
Post a complete minimal example reproducing the problem. We must be able to copy and paste your code in our IDE, compile and run it. My guess is that you modify the matrix after you've stored it in the map.
– JB Nizet
Nov 12 '18 at 20:54
3
Do you mean+=, rather than=+? As it stands, your hash will simply be the hash of the last... row?
– Andy Turner
Nov 12 '18 at 21:00
1
Good catch @AndyTurner! That said, that should still work: it's just a weaker hashCode.
– JB Nizet
Nov 12 '18 at 21:03
|
show 1 more comment
0
0
0
I have a Java class containing a 2D int array. I want to implement the hashCode() method so that different objects can be compared using their attributes and not reference. This is what I tried:
public int hashCode() {
int hash = 0;
for(int i=0; i<getMatrix().length; i++) {
hash =+ Arrays.hashCode(getMatrix()[i]);
}
return hash;
}
I also tried using deepHashCode() but didn't work. My problem is that when the get() method of a HashMap object is used, even though both the object have the same matrix, the get() method does not work properly.
EDIT:
Implementation of equals method
public boolean equals(Object o) {
boolean sameBoard = false;
if(o != null && o instanceof Node) {
Node node = (Node) o;
int board1 = this.getMatrix();
int board2 = node.getMatrix();
return Arrays.deepEquals(board1, board2);
}
return sameBoard;
}
java
asked Nov 12 '18 at 20:45
Sebastian Ampuero MorisakiSebastian Ampuero Morisaki
929
I have a Java class containing a 2D int array. I want to implement the hashCode() method so that different objects can be compared using their attributes and not reference. This is what I tried:
public int hashCode() {
int hash = 0;
for(int i=0; i<getMatrix().length; i++) {
hash =+ Arrays.hashCode(getMatrix()[i]);
}
return hash;
}
I also tried using deepHashCode() but didn't work. My problem is that when the get() method of a HashMap object is used, even though both the object have the same matrix, the get() method does not work properly.
EDIT:
Implementation of equals method
public boolean equals(Object o) {
boolean sameBoard = false;
if(o != null && o instanceof Node) {
Node node = (Node) o;
int board1 = this.getMatrix();
int board2 = node.getMatrix();
return Arrays.deepEquals(board1, board2);
}
return sameBoard;
}
java
java
asked Nov 12 '18 at 20:45
Sebastian Ampuero MorisakiSebastian Ampuero Morisaki
929
asked Nov 12 '18 at 20:45
Sebastian Ampuero MorisakiSebastian Ampuero Morisaki
929
edited Nov 12 '18 at 20:51
Sebastian Ampuero Morisaki
asked Nov 12 '18 at 20:45
Sebastian Ampuero MorisakiSebastian Ampuero Morisaki
929
asked Nov 12 '18 at 20:45
Sebastian Ampuero MorisakiSebastian Ampuero Morisaki
929
asked Nov 12 '18 at 20:45
Sebastian Ampuero MorisakiSebastian Ampuero Morisaki
929
929
1
Did you also implementequals? If so, can you also post your implementation of it as an edit to your post?
– Andrey Akhmetov
Nov 12 '18 at 20:47
@AndreyAkhmetov i posted it
– Sebastian Ampuero Morisaki
Nov 12 '18 at 20:51
2
Post a complete minimal example reproducing the problem. We must be able to copy and paste your code in our IDE, compile and run it. My guess is that you modify the matrix after you've stored it in the map.
– JB Nizet
Nov 12 '18 at 20:54
3
Do you mean+=, rather than=+? As it stands, your hash will simply be the hash of the last... row?
– Andy Turner
Nov 12 '18 at 21:00
1
Good catch @AndyTurner! That said, that should still work: it's just a weaker hashCode.
– JB Nizet
Nov 12 '18 at 21:03
|
show 1 more comment
1
Did you also implementequals? If so, can you also post your implementation of it as an edit to your post?
– Andrey Akhmetov
Nov 12 '18 at 20:47
@AndreyAkhmetov i posted it
– Sebastian Ampuero Morisaki
Nov 12 '18 at 20:51
2
Post a complete minimal example reproducing the problem. We must be able to copy and paste your code in our IDE, compile and run it. My guess is that you modify the matrix after you've stored it in the map.
– JB Nizet
Nov 12 '18 at 20:54
3
Do you mean+=, rather than=+? As it stands, your hash will simply be the hash of the last... row?
– Andy Turner
Nov 12 '18 at 21:00
1
Good catch @AndyTurner! That said, that should still work: it's just a weaker hashCode.
– JB Nizet
Nov 12 '18 at 21:03
1
1
Did you also implement
equals? If so, can you also post your implementation of it as an edit to your post?– Andrey Akhmetov
Nov 12 '18 at 20:47
Did you also implement
equals? If so, can you also post your implementation of it as an edit to your post?– Andrey Akhmetov
Nov 12 '18 at 20:47
@AndreyAkhmetov i posted it
– Sebastian Ampuero Morisaki
Nov 12 '18 at 20:51
@AndreyAkhmetov i posted it
– Sebastian Ampuero Morisaki
Nov 12 '18 at 20:51
2
2
Post a complete minimal example reproducing the problem. We must be able to copy and paste your code in our IDE, compile and run it. My guess is that you modify the matrix after you've stored it in the map.
– JB Nizet
Nov 12 '18 at 20:54
Post a complete minimal example reproducing the problem. We must be able to copy and paste your code in our IDE, compile and run it. My guess is that you modify the matrix after you've stored it in the map.
– JB Nizet
Nov 12 '18 at 20:54
3
3
Do you mean
+=, rather than =+? As it stands, your hash will simply be the hash of the last... row?– Andy Turner
Nov 12 '18 at 21:00
Do you mean
+=, rather than =+? As it stands, your hash will simply be the hash of the last... row?– Andy Turner
Nov 12 '18 at 21:00
1
1
Good catch @AndyTurner! That said, that should still work: it's just a weaker hashCode.
– JB Nizet
Nov 12 '18 at 21:03
Good catch @AndyTurner! That said, that should still work: it's just a weaker hashCode.
– JB Nizet
Nov 12 '18 at 21:03
|
show 1 more comment
0
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1
Did you also implement
equals? If so, can you also post your implementation of it as an edit to your post?– Andrey Akhmetov
Nov 12 '18 at 20:47
@AndreyAkhmetov i posted it
– Sebastian Ampuero Morisaki
Nov 12 '18 at 20:51
2
Post a complete minimal example reproducing the problem. We must be able to copy and paste your code in our IDE, compile and run it. My guess is that you modify the matrix after you've stored it in the map.
– JB Nizet
Nov 12 '18 at 20:54
3
Do you mean
+=, rather than=+? As it stands, your hash will simply be the hash of the last... row?– Andy Turner
Nov 12 '18 at 21:00
1
Good catch @AndyTurner! That said, that should still work: it's just a weaker hashCode.
– JB Nizet
Nov 12 '18 at 21:03