New to Java

hi all,
I am new to java, i tried the following way of finding the indexes of duplicae elements. Please help me with much efficient way with less iterations with out using collection classes

public class Sample {

		 public static void main(String[] args) {
		        String[] strs= {"AA","GG","AA","AA","BOB"};
		        ArrayList equalsList=new ArrayList();
		        for(int i=0;i<=4;i++)
		        {
		        	for(int j=0;j<=4;j++)
		        	{
		        		if(strs!=null && !"".equals(strs[i])&& strs[i]==strs[j] && i!=j)

				{

					

					System.err.println(i+1+ " ---"+ (j+1));

					equalsList.add(i+1);

					

					

					break;

				}

			}

		}

		System.err.println(equalsList);

}
Thanks...