java.lang.UnsupportedOperationException at java.util.AbstractList.remove(Unknown Source)

Question

I have tried below code

String s[]={"1","2","3","4"};  
Collection c=Arrays.asList(s);  
System.out.println(c.remove("1") +"  remove flag");  

System.out.println(" collcetion "+c);  

I was getting

Exception in thread "main" java.lang.UnsupportedOperationException  
at java.util.AbstractList.remove(Unknown Source)  
at java.util.AbstractList$Itr.remove(Unknown Source)  
at java.util.AbstractCollection.remove(Unknown Source)  
at test.main(test.java:26)  

Can anyone help me to solve this issue?

Answer 1

Slight correction: no, it's not an unmodifiable Collection. It just doesn't support adding and removing elements, because it is backed by the supplied array and arrays aren't resizeable. But it supports operations like list.set(index, element)

Answer 2

I was having this problem, because I was also initializing my list with Arrays.asList:

List<String> names = Arrays.asList("a", "b", "c");

To solve the problem, I used addAll instead:

List<String> names = new ArrayList<String>();
names.addAll(Arrays.asList("a", "b", "c"));

This way you can edit the list, add new items or remove.

Answer 3

The List returned by Arrays.asList method of java.util.Arrays class is a fixed-size list object which means that elements cannot be added to or removed from the list.

So functions like Adding or Removing cannot be operated on such kind of Lists.

The solution to adding or removing without getting java.lang.UnsupportedOperationException is ->

List<String> strList= new ArrayList<>(Arrays.asList(strs));

//Then Add or Remove can be called on such List

newList.add("100");
newList.remove("100");

Answer 4

A one liner fix is to declare your list like this:

List<Integer> list2 = new ArrayList<>(Arrays.asList(0,8,1,5,7,0));

Answer 5

The following method

private void printCollection() {
  List<String> strings = new ArrayList<>(Arrays.asList("1", "2", "3", "4"));

  System.out.println(strings.remove("1") + " remove flag");
  System.out.println("collection " + strings);
}

Will print

true remove flag
collection [2, 3, 4]

Note that true is the (successful) return value from remove().