implement strstr()

public class Solution{
	public int strStr(String haystack , String needle){
		int l1 = haystack.length();
		int l2 = needle.length();
		
		if(l1 == 0 && l2 == 0)
		return -1;
		
		int count = 0;
		String str = "";
		for(; count < l1 - l2 + 1 ; count++){
			str = haystack.substring(count , count + l2);
			if(str.equals(needle))
			break;
		}
		return str.equals(needle) ? count : -1;
	}
}