The output is: [a, b, c] [a, b, c, c] Why is the output left to right? Is the insertElementAt 1-based instead of zero based?

ExtendedStack.java

/**
 *	This class extends the Stack 
 *	so that there's a pushdown(i)
 *	method which copies the elements
 *	at index 0 and inserts it and index i.
 * All items beneath index i are pushed down.
 *
 */

import java.util.Stack;
import java.util.Arrays;

public class ExtendedStack<T> extends Stack<T> {

	public static void main(String[] args)
	{
			ExtendedStack<String> e = new ExtendedStack<String>();
			
			e.push("a");
			e.push("b");
			e.push("c");

			e.dumpContents();

			Integer element = 2;
			
			e.pushdown(element);
			e.dumpContents();
	}

	public void pushdown(int i)
	{
		this.insertElementAt(this.peek(), i);
	}

	/**
	*	Dump the contents of the stack.
	*/
	public void dumpContents(){
		System.out.println(Arrays.toString(this.toArray()));
    }
}