Using asList with Generics

[Jerret Halter]

I am trying to preform the following:

package learning.about.collection;
 
import java.util.*;
 
public class Fubar {
 
/**
 * @param args
 */
public static void main(String[] args) {
List<Integer> myList = new ArrayList<Integer>();
String[] myArray = {"d", "c", "z", "q"};
List<String> foo = Arrays.asList(myArray);

foo.add("a");
myList.add(22);
myList.add(20);
myList.add(12);

Collections.sort(myList);
Arrays.sort(myArray);


System.out.println("myList = " + myList);
System.out.print("myArray = ");
for(String s : myArray){
System.out.print(s + " ");
}
System.out.println("\nfoo = " + foo);
}
 
}

But the following exception is thrown when I try to run it:

Exception in thread "main" java.lang.UnsupportedOperationException
at java.util.AbstractList.add(Unknown Source)
at java.util.AbstractList.add(Unknown Source)
at learning.about.collection.Fubar.main(Fubar.java:15)

I only have Java 1.5 on my machine, so what is going wrong here?

Thanks in advance :-)

[Henry Wong]

But the following exception is thrown when I try to run it:

Exception in thread "main" java.lang.UnsupportedOperationException
at java.util.AbstractList.add(Unknown Source)
at java.util.AbstractList.add(Unknown Source)
at learning.about.collection.Fubar.main(Fubar.java:15)

I only have Java 1.5 on my machine, so what is going wrong here?

Thanks in advance :-)

The Arrays.asList() method returns a list that is *backed* by the array. Since it is not possible to resize an array, you are not allowed to add or removed from the list.

Henry

[Jerret Halter]

So what you are saying is that I can use Arrays.asList() it will build a List, however I can only add to the Array?

[Henry Wong]

Originally posted by Jerret Halter:
So what you are saying is that I can use Arrays.asList() it will build a List, however I can only add to the Array?

The list that you get back from the asList() method can only be used like an array. You can set() a value at an index. You can get() a value at an index. But you can't add an element or remove an element, because you can't grow or shrink an array.

Henry

[Jerret Halter]

ICIC thanks a bunch.

[Burkhard Hassel]

Howdy,

what you could do instead in a situation like this is to make a new list out of the array, the array would copied into the list, and you can add things to it.
So instead of saying
String[] myArray = {"d", "c", "z", "q"};
List<String> foo = Arrays.asList(myArray);

you say
String[] myArray = {"d", "c", "z", "q"};
List<String> foo = new ArrayList( Arrays.asList(myArray) );
foo.add("Halloween ");
System.out.println(foo);




Yours,
Bu.

[Jerret Halter]

Ah, very nice, and ArrayList are much nicer :-)