求字符串数组最长公共前缀

public class LongestCommonPrefix {

public String longestCommonPrefix(String[] strs)
{
if(strs == null)
return null;
if(strs.length == 0)
return "";
String s = strs[0];
for(int i = 0; i < s.length(); i ++)
{
for(int j = 1; j < strs.length; j ++)
{
if(strs[j].length()==i||strs[j].charAt(i)!= s.charAt(i))//条件先后顺序不能写反了，否则数组越界
return s.substring(0,i);
}
}
return s;
}
public static void main(String[] args) {
LongestCommonPrefix lc = new LongestCommonPrefix();
String[] strs = {"aa" , "a"};
System.out.println(lc.longestCommonPrefix(strs));
}

}