String 类型强制转换 float 四舍五入

import java.math.BigDecimal;
//遍历maplist 
List<Map<String, Object>> oldList = new ArrayList<Map<String, Object>>();
try {
for (Map<String, Object> mapList : list) {
//将key强制转换为string
String mString=String.valueOf(mapList.get("subtotal"));
String nString=String.valueOf(mapList.get("total"));
 //string 转换float
float x = Float.valueOf(mString.trim()).floatValue();
float y = Float.valueOf(nString.trim()).floatValue();
float z = (x / y) * 100;
 //将float转换为可以精确计算类型BigDecimal
BigDecimal b = new BigDecimal(z);
//四舍五入保留小数点后两位
float f1 = b.setScale(2, BigDecimal.ROUND_HALF_UP).floatValue();
//mapList添加(key,value)
mapList.put("perc", f1);
//将数据添加到列表
oldList.add(mapList);
}
} catch (NumberFormatException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}