使用java而不使用*运算符的十进制乘法

The below code works accurate on int

以下代码在int上运行准确

public class Example {
    public static void main(String[] args) {

        int a = 3, b = 3, mul = 0;

        // mul = a * b //this should not be used

        for (int i = 1; i <= a; i++)
            mul = mul + b;

        System.out.println(a + "*" + b + "-->" + mul);
    }
}

output : 3*3-->9 Now this is perfect

输出:3 * 3 - > 9现在这是完美的

But when i used double :

但是,当我使用双倍:

public class Example {
    public static void main(String[] args) {

        double a = 3.5, b = 3.5, mul = 0;

        // mul = a * b //this should not be used

        for (int i = 1; i <= a; i++)
            mul = mul + b;

        System.out.println(a + "*" + b + "-->" + mul);
    }
}

output:

3.5*3.5-->10.5 Now this is wrong since the correct answer of

3.5 * 3.5 - > 10.5现在这是错误的,因为正确的答案

3.5*3.5-->12.25

The problem is i need to multiply decimal values where as for loop wont support iteration over double value.

问题是我需要乘以十进制值,因为循环不支持迭代超过double值。

4 个解决方案

#1

You can convert your decimal values to integer with divide by 0,(0..)1. After operation you should divide by 1(0..).

您可以将十进制值转换为除以0的整数,(0 ..)1。操作后,您应该除以1(0 ..)。

Ex: 3,5*3,5 = (3,5/0,1)*(3,5/0,1)/100 = 35*35/100 = 12,25

例:3,5 * 3,5 =(3,5 / 0,1)*(3,5 / 0,1)/ 100 = 35 * 35/100 = 12,25

Code;

 private double multiplication(double d1, double d2) {

        double divDiff1 = 1, divDiff2 = 1;

        while (d1 != Math.floor(d1)) {
            d1 = Double.valueOf(String.format("%.6f", d1 / 0.1));
            divDiff1 = divDiff1 / 0.1;
        }
        while (d2 != Math.floor(d2)) {
            d2 = Double.valueOf(String.format("%.6f", d2 / 0.1));
            divDiff2 = divDiff2 /0.1;
        }

        double mul = 0;
        for (int i = 1; i <= d1; i++)
            mul = mul + d2;

        return mul / divDiff2 / divDiff1;
    }

Call like below;

打电话如下;

multiplication(2.5,1.6);

#2

Count decimal places, convert the numbers to integers, multiply via addition with loops, then reinsert your decimal place.

计算小数位数,将数字转换为整数,通过加法与循环相乘,然后重新插入小数位。

3.5 x 3.5 becomes 35 x 35, and then the decimal point is shifted 2 places to the left to give you your answer.

3.5 x 3.5变为35 x 35,然后小数点向左移动2位,为您提供答案。

#3

The explanation of such behavior is explained in this post - Java Double Multiplication explanation?

这个行为的解释在这篇文章中解释了 - Java Double Multiplication的解释?

To resolve such issue it is best to use BigDecimal.

要解决此类问题,最好使用BigDecimal。

BigDecimal d1 = new BigDecimal("3.5");
BigDecimal d2 = new BigDecimal("3.5");
BigDecimal result = d1.multiply(d2);
System.out.printf("%s * %s = %s%n", d1, d2, result);

#4

STEPS:

Ignore the decimal point and convert those numbers to integers

忽略小数点并将这些数字转换为整数

Then Multiply them using additions (as you have done for integers)

然后使用加法将它们相乘(就像你对整数所做的那样)

Convert the answer to string and place the decimal at its place.

将答案转换为字符串并将小数放在其位置。

You will need String and StringBuilder for this.

您将需要String和StringBuilder。

Here is the code:

这是代码:

    double a = 3.5, b = 3.5;

    StringBuilder num1 = new StringBuilder(Double.toString(a));
    StringBuilder num2 = new StringBuilder(Double.toString(b));

    int indexOfDecimalPointFromBeginning_num1 = num1.indexOf(".");
    int indexOfDecimalPointFromBeginning_num2 = num2.indexOf(".");

    int decimalCounterNum1 = num1.length() - indexOfDecimalPointFromBeginning_num1 - 1;
    int decimalCounterNum2 = num2.length() - indexOfDecimalPointFromBeginning_num2 - 1;

    int decimalCountForResult = decimalCounterNum1 + decimalCounterNum2;

    String num1_withoutDecimal = num1.deleteCharAt(indexOfDecimalPointFromBeginning_num1).toString();
    String num2_withoutDecimal = num2.deleteCharAt(indexOfDecimalPointFromBeginning_num2).toString();

    int newNum1 = Integer.parseInt(num1_withoutDecimal);
    int newNum2 = Integer.parseInt(num2_withoutDecimal);

    int tempMul = 0;

    for (int i = 1; i <= newNum1; i++) {
        tempMul = tempMul + newNum2;
    }

    StringBuilder finalAnswer = new StringBuilder(Integer.toString(tempMul));
    finalAnswer.insert(finalAnswer.length() - decimalCountForResult, ".");

    Double finalAnswerInDouble = Double.parseDouble(finalAnswer.toString());
    System.out.println(a + "*" + b + " --> " + finalAnswer.toString());

#1