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UnsupportedOperationException While removing [duplicate]

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1

This question already has an answer here:

• 
  remove() on List created by Arrays.asList() throws UnsupportedOperationException
  
  3 answers
  
  

I am trying to remove duplicates from an ArrayList. But I keep getting this UnsupportedOperationException

public static void removeDuplicates(List<Integer> list) 
 Collections.sort(list);

 for(int i = 0; i<list.size();i++) 
 if(list.get(i)== list.get((i+1))) 
 list.remove(i+1);
 

 

 

One thing I cannot create a new list and change it because I shouldn't return anything. I have to change the list in place.

java

share|improve this question

edited Mar 8 at 0:27

Yojan Gautam

asked Mar 7 at 23:59

Yojan GautamYojan Gautam

64

marked as duplicate by Tom, Andreas, Stephen C java
Users with the  java badge can single-handedly close java questions as duplicates and reopen them as needed.

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Mar 8 at 0:24

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Likely your List is some form of unmodifiable list, such as one created by Arrays.asList( int[] ).
  
  – Roddy of the Frozen Peas
  Mar 8 at 0:01
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Also, don't use == for Integer, use equals().
  
  – Gendarme
  Mar 8 at 0:03
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @RoddyoftheFrozenPeas No, there wouldn't be a ConcurrentModificationException.
  
  – Tom
  Mar 8 at 0:03
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Well you have to change your design. You fundamentally cannot remove an element from an array. The Java language spec and the JVM spec do not allow this. (And if you can't change the design, or figure out an alternative way that doesn't involve changing the array's length, you need to consider abandoning the project entirely. This is a bit like saying, "I need to modify maths so that 1 + 1 is 3 for my project". It won't work.)
  
  – Stephen C
  Mar 8 at 0:26
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I think it is more likely that you have not understood what your professor is really saying and/or asking you to do. Go talk to him ... and be prepared to "eat humble pie".
  
  – Stephen C
  Mar 8 at 0:31
  
  

  
  
  
  

 | 
show 9 more comments

1

This question already has an answer here:

• 
  remove() on List created by Arrays.asList() throws UnsupportedOperationException
  
  3 answers
  
  

I am trying to remove duplicates from an ArrayList. But I keep getting this UnsupportedOperationException

public static void removeDuplicates(List<Integer> list) 
 Collections.sort(list);

 for(int i = 0; i<list.size();i++) 
 if(list.get(i)== list.get((i+1))) 
 list.remove(i+1);
 

 

 

One thing I cannot create a new list and change it because I shouldn't return anything. I have to change the list in place.

java

share|improve this question

edited Mar 8 at 0:27

Yojan Gautam

asked Mar 7 at 23:59

Yojan GautamYojan Gautam

64

marked as duplicate by Tom, Andreas, Stephen C java
Users with the  java badge can single-handedly close java questions as duplicates and reopen them as needed.

StackExchange.ready(function()
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$('.dupe-hammer-message-hover:not(.hover-bound)').each(function()
var $hover = $(this).addClass('hover-bound'),
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$hover.hover(
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$hover.showInfoMessage('',
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position: my: 'bottom left', at: 'top center', offsetTop: -7 ,
dismissable: false,
relativeToBody: true
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,
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StackExchange.helpers.removeMessages();

);
);
);
Mar 8 at 0:24

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Likely your List is some form of unmodifiable list, such as one created by Arrays.asList( int[] ).
  
  – Roddy of the Frozen Peas
  Mar 8 at 0:01
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Also, don't use == for Integer, use equals().
  
  – Gendarme
  Mar 8 at 0:03
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @RoddyoftheFrozenPeas No, there wouldn't be a ConcurrentModificationException.
  
  – Tom
  Mar 8 at 0:03
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Well you have to change your design. You fundamentally cannot remove an element from an array. The Java language spec and the JVM spec do not allow this. (And if you can't change the design, or figure out an alternative way that doesn't involve changing the array's length, you need to consider abandoning the project entirely. This is a bit like saying, "I need to modify maths so that 1 + 1 is 3 for my project". It won't work.)
  
  – Stephen C
  Mar 8 at 0:26
  
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I think it is more likely that you have not understood what your professor is really saying and/or asking you to do. Go talk to him ... and be prepared to "eat humble pie".
  
  – Stephen C
  Mar 8 at 0:31
  
  

  
  
  
  

 | 
show 9 more comments

This question already has an answer here:

• 
  remove() on List created by Arrays.asList() throws UnsupportedOperationException
  
  3 answers
  
  

I am trying to remove duplicates from an ArrayList. But I keep getting this UnsupportedOperationException

public static void removeDuplicates(List<Integer> list) 
 Collections.sort(list);

 for(int i = 0; i<list.size();i++) 
 if(list.get(i)== list.get((i+1))) 
 list.remove(i+1);
 

 

 

One thing I cannot create a new list and change it because I shouldn't return anything. I have to change the list in place.

java

share|improve this question

edited Mar 8 at 0:27

Yojan Gautam

asked Mar 7 at 23:59

Yojan GautamYojan Gautam

64

public static void removeDuplicates(List<Integer> list) 
 Collections.sort(list);

 for(int i = 0; i<list.size();i++) 
 if(list.get(i)== list.get((i+1))) 
 list.remove(i+1);
 

 

 

share|improve this question

edited Mar 8 at 0:27

Yojan Gautam

asked Mar 7 at 23:59

Yojan GautamYojan Gautam

64

share|improve this question

edited Mar 8 at 0:27

Yojan Gautam

asked Mar 7 at 23:59

Yojan GautamYojan Gautam

64

asked Mar 7 at 23:59

Yojan GautamYojan Gautam

64

asked Mar 7 at 23:59

Yojan GautamYojan Gautam

64

1 Answer
1

active

oldest

votes

-1

You cannot remove elements whilst iterating over it using a for loop. A simple way around this is to create a new ArrayList containing your original lists elements and then loop over the original list removing duplicates from your copy of the list and then return that.

Even if you could remove elements using a for loop the other thing this could be is if the list of type UnmodifiableCollection? If so you cannot remove elements from it, which is the point of the class. Again a solution would be to create a brand new ArrayList which copies the original elements and remove and alter that however you like and return that to the calling code.

share|improve this answer

answered Mar 8 at 0:03

tomgeraghty3tomgeraghty3

43128

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Actually, in some cases you can remove elements while iterating a list. If you are indexing the list, it is OK. And if you are iterating with an iterator (explicitly) you can use Iterator::remove. The OP's could would work provided that this was a list that supported remove ... and he corrected the bugs in the indexing; e.g. get(i+1) when i == list.length() - 1.
  
  – Stephen C
  Mar 8 at 0:13
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I agree about the remove() of Iterator. Can you explain what you mean by 'if you are indexing the list'
  
  – tomgeraghty3
  Mar 8 at 0:15
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Using using a loop to iterate over the indexes of an array and get(index), set(index), remove(index) etcetera. Basically, what the OP's example does!
  
  – Stephen C
  Mar 8 at 0:35
  
  

  
  
  
  

add a comment | 

-1

You cannot remove elements whilst iterating over it using a for loop. A simple way around this is to create a new ArrayList containing your original lists elements and then loop over the original list removing duplicates from your copy of the list and then return that.

Even if you could remove elements using a for loop the other thing this could be is if the list of type UnmodifiableCollection? If so you cannot remove elements from it, which is the point of the class. Again a solution would be to create a brand new ArrayList which copies the original elements and remove and alter that however you like and return that to the calling code.

share|improve this answer

answered Mar 8 at 0:03

tomgeraghty3tomgeraghty3

43128

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Actually, in some cases you can remove elements while iterating a list. If you are indexing the list, it is OK. And if you are iterating with an iterator (explicitly) you can use Iterator::remove. The OP's could would work provided that this was a list that supported remove ... and he corrected the bugs in the indexing; e.g. get(i+1) when i == list.length() - 1.
  
  – Stephen C
  Mar 8 at 0:13
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I agree about the remove() of Iterator. Can you explain what you mean by 'if you are indexing the list'
  
  – tomgeraghty3
  Mar 8 at 0:15
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Using using a loop to iterate over the indexes of an array and get(index), set(index), remove(index) etcetera. Basically, what the OP's example does!
  
  – Stephen C
  Mar 8 at 0:35
  
  

  
  
  
  

add a comment | 

-1

You cannot remove elements whilst iterating over it using a for loop. A simple way around this is to create a new ArrayList containing your original lists elements and then loop over the original list removing duplicates from your copy of the list and then return that.

Even if you could remove elements using a for loop the other thing this could be is if the list of type UnmodifiableCollection? If so you cannot remove elements from it, which is the point of the class. Again a solution would be to create a brand new ArrayList which copies the original elements and remove and alter that however you like and return that to the calling code.

share|improve this answer

answered Mar 8 at 0:03

tomgeraghty3tomgeraghty3

43128

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Actually, in some cases you can remove elements while iterating a list. If you are indexing the list, it is OK. And if you are iterating with an iterator (explicitly) you can use Iterator::remove. The OP's could would work provided that this was a list that supported remove ... and he corrected the bugs in the indexing; e.g. get(i+1) when i == list.length() - 1.
  
  – Stephen C
  Mar 8 at 0:13
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I agree about the remove() of Iterator. Can you explain what you mean by 'if you are indexing the list'
  
  – tomgeraghty3
  Mar 8 at 0:15
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Using using a loop to iterate over the indexes of an array and get(index), set(index), remove(index) etcetera. Basically, what the OP's example does!
  
  – Stephen C
  Mar 8 at 0:35
  
  

  
  
  
  

add a comment | 

You cannot remove elements whilst iterating over it using a for loop. A simple way around this is to create a new ArrayList containing your original lists elements and then loop over the original list removing duplicates from your copy of the list and then return that.

Even if you could remove elements using a for loop the other thing this could be is if the list of type UnmodifiableCollection? If so you cannot remove elements from it, which is the point of the class. Again a solution would be to create a brand new ArrayList which copies the original elements and remove and alter that however you like and return that to the calling code.

share|improve this answer

answered Mar 8 at 0:03

tomgeraghty3tomgeraghty3

43128

share|improve this answer

answered Mar 8 at 0:03

tomgeraghty3tomgeraghty3

43128

answered Mar 8 at 0:03

tomgeraghty3tomgeraghty3

43128

answered Mar 8 at 0:03

tomgeraghty3tomgeraghty3

43128