为什么要用toString()方法将double值表示为字符串对象

Question

public class UseCase {

public static BigDecimal div(double value1,double value2,int b,int r){
    if(b<0){
        System.out.println("b值必须大于等于0");
    }
    BigDecimal b1=new BigDecimal(Double.toString(value1)); 
    BigDecimal b2=new BigDecimal(Double.toString(value2));
    /*为什么要用toString()方法将double值表示为字符串对象*/

    return b1.divide(b2,b,r);
}
public static void main(String[] args) {
    // TODO 自动生成方法存根
    UseCase u=new UseCase();
    System.out.println(u.div(-7.5,8.9,5,BigDecimal.ROUND_CEILING));
    System.out.println(u.div(-7.5,8.9,5,BigDecimal.ROUND_DOWN));
    System.out.println(u.div(-7.5,8.9,5,BigDecimal.ROUND_FLOOR));
    System.out.println(u.div(-7.5,8.9,5,BigDecimal.ROUND_HALF_DOWN));
    System.out.println(u.div(-7.5,8.9,5,BigDecimal.ROUND_HALF_EVEN));
    System.out.println(u.div(-7.5,8.9,5,BigDecimal.ROUND_HALF_UP));
    System.out.println(u.div(-7.5,8.9,5,BigDecimal.ROUND_UP));
}

}

Answer 1

toString是带有四舍五入的，BigDecimal直接从double获取不会四舍五入，主要就是这个区别。