List converted from an Array

[m ali]

Hi All,

Why the following code giving UnsupportedOperationException at Line1 when running the program? Can't we able to remove a value from list, which is converted from an array? please explain?

  
import java.util.*;
class RemList {
public static void main(String [] args) {
String [] sa = {"one", "two", "three", "four"};
List <String> st=Arrays.asList(sa);
System.out.print(st);
st.remove(2);                          // line 1
System.out.print(st+ "\n");
for(String s : sa) {
System.out.print(s+"  ");
}
}

}
 

  

Thanks in Advance.

[Chandra Bhatt]

Hi Ali,

import java.util.*;
class RemList {
public static void main(String [] args) {
String [] sa = {"one", "two", "three", "four"};
List <String> st=Arrays.asList(sa);
System.out.print(st);
st.remove(2);                          // line 1
System.out.print(st+ "\n");
for(String s : sa) {
System.out.print(s+"  ");
}
}

}

asList() method of ArrayList returns fixed sized ArrayList.
And this ArrayList is not the List that implements List interface,
but sub class of Arrays class.

Try this:

System.out.println(Arrays.asList(sa).getclass());

You will get the output as:
java.util.Arrays$ArrayList

and prove your answer with this code:

System.out.println(Arrays.asList(sa) instanceof java.util.ArrayList); //false

Arrays.ArrayList extends AbstractList class that implement List
interface.

System.out.println(Arrays.asList(sa) instanceof java.util.ArrayList);
//returns true

What operation is supported in that are:
get() and set()
remove() and add() throws UnsupportedOperationException, because these
operations are not supported by it.

And yeah, one more thing; if you use the set() method on the list it
will reflect the array also and vice versa;
Check it out!!!





Regards,
cmbhatt
[ April 23, 2007: Message edited by: Chandra Bhatt ]

[m ali]

Hi Chandra,

Thanks for Explanation. I got it.

Thank you.