Collections.synschronizedList

[SaravanaKumar Venugopal]

Hi All,

Can any one tell me how to modify the value of a synchronized list, given below is the snippet, when I tried it thrown UnsupportedOperation Exception

List<String> listOfString = new ArrayList<>();
listOfString.add("value1")
listOfString.add("value2")
listOfString.add("value3")


List<String> syncList = Collections.synschronizedList(listOfString);
syncList.add("value4"); // throws UnsupportedOperation (even I have tried placing under synchronized block)

[Keith Lynn]

I tried your code, and it worked without a problem. (after fixing syntax errors)

[SaravanaKumar Venugopal]

Thanks for the prompt response Keith Lynn

Am sorry the code was like given below and it thrown UnsupportedOperationException and when I googled it has been said as when we convert to list by Arrays.asList() which will return fixed size of list and when we try to modify we will be getting UnsupportedOperationException. And there is no issue with the original post.

<code>
String s1 = "Value1,Value2,Value3,Value4";
List<String> lStr1 = Arrays.asList(s1.split(","));

lStr1.add("");
</code>

[Campbell Ritchie]

Let's have a look at the documentation for Collections#synchronizedList. It gives all sorts of dire warnings about what can go wrong if you don't synchronise the List correctly, but there is no suggestion of an unsupported operation Exception. You do get that Exception if you create the List with this method, however.

[Winston Gutkowski]

SaravanaKumar Venugopal wrote:And there is no issue with the original post.

Erm...yes there is:

  listOfString.add("value1")

is NOT a valid Java statement because it is missing a final ';'.

Could you also please read the page about using code tags, because our site does not use HTML tags.

Thanks.

Winston

[Keith Lynn]

SaravanaKumar Venugopal wrote:Thanks for the prompt response Keith Lynn

Am sorry the code was like given below and it thrown UnsupportedOperationException and when I googled it has been said as when we convert to list by Arrays.asList() which will return fixed size of list and when we try to modify we will be getting UnsupportedOperationException. And there is no issue with the original post.

<code>
String s1 = "Value1,Value2,Value3,Value4";
List<String> lStr1 = Arrays.asList(s1.split(","));

lStr1.add("");
</code>

In your original post, you were converting a list to a synchronized list. When you do that, you can add to it.

In this example, you are taking an array and treating it as a list.

But since it is still an actual array, you cannot add to it.