Name: auR10023 Date: 01/03/2001



The javadoc for java.util.Collections.rotate(List,int) method says:

...
Throws:
          UnsupportedOperationException - if the specified list or its list-iterator does not
          support the set method.
...

Following example shows that UnsupportedOperationException is not thrown by this method.
Here is the example:

------t.java-----
import java.util.*;

    class TestList extends Vector {
        public TestList() {
            super();
        }
        public TestList(Collection c) {
            super(c);
        }
        public Object set(int index, Object element) {
            throw new UnsupportedOperationException();
        }
        public List subList(int fromIndex, int toIndex) {
            return new TestList(super.subList(fromIndex, toIndex));
        }
    }

    class TestList1 extends Vector {
        public TestList1() {
            super();
        }
        public TestList1(Collection c) {
            super(c);
        }
        public List subList(int fromIndex, int toIndex) {
            return new TestList1(super.subList(fromIndex, toIndex));
        }
        public ListIterator listIterator() {
            return new TestIter(super.listIterator());
        }
        public ListIterator listIterator(int index) {
            return new TestIter(super.listIterator(index));
        }
    }

    class TestIter implements ListIterator {
        private ListIterator iter;
        public TestIter (ListIterator iter) {
            this.iter = iter;
        }
        public boolean hasNext() {
            return iter.hasNext();
        }
        public Object next() {
            return iter.next();
        }
        public boolean hasPrevious() {
            return iter.hasPrevious();
        }
        public Object previous() {
            return iter.previous();
        }
        public int nextIndex() {
            return iter.nextIndex();
        }
        public int previousIndex() {
            return iter.previousIndex();
        }
        public void remove() {
            iter.remove();
        }
        public void set(Object o) {
            throw new UnsupportedOperationException();
        }
        public void add(Object o) {
            iter.add(o);
        }
    }

public class t {
    public static void main(String[] args){
        Vector v = new TestList();
        Vector v1 = new TestList1();
        v.add(new Integer(1));
        v1.add(new Integer(1));

        try {
            Collections.rotate(v,1);
            System.out.println("First exception is not raised");
        } catch (UnsupportedOperationException e) {
            System.out.println("First exception raised");
        }

        try {
            Collections.rotate(v,1);
            System.out.println("Second exception is not raised");
        } catch (UnsupportedOperationException e) {
            System.out.println("Second exception raised");
        }
    }
}

----output:----

First exception is not raised
Second exception is not raised

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