Vector

[Shiva Mohan]

/*
import java.util.*;
public class Java_Collection {

public static void main(String args[]){

List theList=new Vector();

theList.add(0, "Chicago");

theList.add(1, "Vegas");
theList.add(4, "Jersey");



Iterator it=theList.iterator();
while(it.hasNext()){
System.out.println(it.next());
}
}
*/

}

1.why the program is throwing runtime Exception?List is sorted by index and i was expecting the answer.

2.when i search javaranch,i found lots of questions as Arrays.asList.For SCJP1.4 exam,do i need to know about Arrays class and its methods.

please help on the above two questions

[Chandra Bhatt]

List theList=new Vector();
 
theList.add(0, "Chicago");
 
theList.add(1, "Vegas");
theList.add(4, "Jersey");

Hi Shiv,

what about index position 2 and 3. You directly jumped to index 4. That is why java.lang.ArrayIndexOutOfBoundsException was thrown by JVM.


Regards,
cmbhatt

[Shiva Mohan]

Chandra,Thanks for the reply.

Do we need to give all the index numbers in order.it may be a silly question,but Collection is entierly new for me.
Then what is the purpose of ordering since ordering is done by index?

[Chandra Bhatt]

Originally posted by Shiv
Then what is the purpose of ordering since ordering is done by index?

Actually the basic use (and often used) of the add(index,Object) is to provide something you call resetting the Object at given index.

When you simply use:
add(Object);
It is added sequentially in the list. But giving index, it goes to that position and sets the Object. I use "sets" because its soul purpose it that. From scratch adding object to the collection by giving it the index position as first argument is like you add to the array (clumsy way).

Collection made it convenient; taking care of indexes itself.


Regards,
cmbhatt

[Srinivas Kalvala]

Hello,

The size of the vector will be verified with the index position when a new object is being added.

If the size of the Vector is less than index position then java.lang.ArrayIndexOutOfBoundsException will be thrown.

Have a look at java source.

Note: The add method inturn will call following method.

/**
     * Inserts the specified object as a component in this vector at the 
     * specified <code>index</code>. Each component in this vector with 
     * an index greater or equal to the specified <code>index</code> is 
     * shifted upward to have an index one greater than the value it had 
     * previously. <p>
     *
     * The index must be a value greater than or equal to <code>0</code> 
     * and less than or equal to the current size of the vector. (If the
     * index is equal to the current size of the vector, the new element
     * is appended to the Vector.)<p>
     *
     * This method is identical in functionality to the add(Object, int) method
     * (which is part of the List interface). Note that the add method reverses
     * the order of the parameters, to more closely match array usage.
     *
     * @param      obj     the component to insert.
     * @param      index   where to insert the new component.
     * @exception  ArrayIndexOutOfBoundsException  if the index was invalid.
     * @see        #size()
     * @see   #add(int, Object)
     * @see   List
     */
    public synchronized void insertElementAt(E obj, int index) {
modCount++;
if (index > elementCount) {
    throw new ArrayIndexOutOfBoundsException(index
     + " > " + elementCount);
}
ensureCapacityHelper(elementCount + 1);
System.arraycopy(elementData, index, elementData, index + 1, elementCount - index);
elementData[index] = obj;
elementCount++;
    }
 
 

[ April 11, 2007: Message edited by: Srinivas Kalvala ]
[ April 11, 2007: Message edited by: Srinivas Kalvala ]