替换指定指针后的字符串

/**
* 替换指定指针后的字符串
* @param str yyyyMMdd
* @param subInt  要截取的指针
* @return replaceStr  要替换的str  
* @return str  
*/
public static String getSubString(String str,int subInt ,String replaceStr){
// str = "20160712";
if(str.length()> subInt){
String a = str.substring(0,subInt);
String b = str.substring(subInt);
// System.out.println("----nowtime:a"+a);//201607
// System.out.println("----nowtime:b"+b);//12
str = a+replaceStr;
}
return str;
}