Java Tips

字符串拼接

// append方法最快
str = new StringBuilder(str).append("长安十二时辰").toString();

时间计算

Calendar dateNow = Calendar.getInstance();
dateNow.add(Calendar.DAY_OF_YEAR, 14);//日期加14天
dateNow.add(Calendar.YEAR,-1);//日期减1年
dateNow.add(Calendar.MONTH,3);//日期加3个月
Date caTime = dateNow.getTime();

获取时间戳

// 毫秒
String timestamp= String.valueOf(System.currentTimeMillis() / 1000);
// 秒
String timestamp= String.valueOf(System.currentTimeMillis());

遍历Map

Map map= new HashMap();
Iterator iter = map.entrySet().iterator();
while (iter.hasNext()) {
  Map.Entry entry = (Map.Entry) iter.next();
  Object key =  entry.getKey();
  Object value = entry.getValue();
}