Java 日期计算的问题

String lastSubmitDate = "2010-06-01";

如何将字符串lastSubmitDate 加上7天呀，也就是变成"2010-06-08";
求高手 支招呀，谢谢了。

[code="java"]
String lastSubmitDate = "2010-06-01";
SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
Date d=sdf.parse(lastSubmitDate);
long l=d.getTime()+7*24*60*60*1000l;
d=new Date(l);
lastSubmitDate=sdf.format(d);
System.out.println(lastSubmitDate);
[/code]

lastSubmitDate.substring(0,lastSubmitDate.length()-2) + Integer.toString(Integer.parseInt(lastSubmitDate.substring(lastSubmitDate.length()-2))+7)

[code="java"]
String strDate = "2010-06-01";
SimpleDateFormat objFormat = new SimpleDateFormat("yyyy-MM-dd");
Date toDate = objFormat.parse(strDate);
toDate.setDate(toDate.getDate()+7);
System.out.println(objFormat.format(toDate));
[/code]