Não consigo usar o método Swap

import java.util.ArrayList;
import java.util.Collections;

class InsertionSort
{
	public Object insertionSort(Object array[], int startIdx, int endIdx) 
	{
		for (int i = startIdx; i < endIdx; i++) 
		{
			int k = i;
			for (int j = i + 1; j < endIdx; j++) 
			{
				if ((array[k]).compareTo(array[j])>0) 
				{
					k = j;
				}
			}
			Collections.swap(array,i,k);
		}
		return array;
	}
	public static void main(String args[])
	{
		String[] array = {"David","Luiz","Pedro"};
		InsertionSort is = new InsertionSort();
		System.out.println((String)is.insertionSort(array,0,7));
	}
}

C:\Documents and Settings\David\Desktop\Java>javac InsertionSort.java -Xlint
InsertionSort.java:13: warning: [unchecked] unchecked call to compareTo(T) as a
member of the raw type java.lang.Comparable
                                if (((Comparable) array[k]).compareTo(array[j])>
0)
                                                                     ^
InsertionSort.java:18: swap(java.lang.Object[],int,int) has private access in ja
va.util.Collections
                        Collections.swap(array,i,k);
                                   ^
1 error
1 warning