检查这两个数字是否等于n位有效数字

Question

I figured out the main portion of the code but I can't figure out how to get it so it will only read the difference up to the however many decimal points the user inputs. So how would I go about being able to take the user input( it would be third number typed in) and find the whether the first two numbers are equal to that decimal point. The goal of the program is to check if the two numbers are equal to n(a number the user inputs) significant digits.

Sample Input: 5.124 5.125 2

Sample output: Difference = .001 , Numbers are equal to 2 decimal places

import java.util.Scanner;
public class Equal {

    public static void main(String[] args) {
        Scanner input = new Scanner( System.in );
        String diff="diffrence =";
        double num1;
        double num2; 
        double num3;
        double calc;
        while(input.hasNext()){
            num1 = Double.parseDouble(input.next());
            num2 = Double.parseDouble(input.next());
            num3 = Double.parseDouble(input.next());
            calc = Math.abs(num1-num2);
            System.out.printf("%s %.10f", diff, calc);
        }
    }
}

Answer 1

Here is an example and a junit test case for ordinary doubles. Hope this helps.

public boolean doublesSameNumberOfDecimalPlaces(double x,double y,int numberOfDecimals){
    x = (long)(x * Math.pow(10, numberOfDecimals));
    y = (long)(y * Math.pow(10, numberOfDecimals));
    return x==y;
}

@Test
public void TestDoublesSameNumberOfDecimalPlaces(){
    double x = 3.141593;
    double y = 3.14159265359;
    assertTrue(doublesSameNumberOfDecimalPlaces(x,y,0));
    assertTrue(doublesSameNumberOfDecimalPlaces(x,y,1));
    assertTrue(doublesSameNumberOfDecimalPlaces(x,y,2));
    assertTrue(doublesSameNumberOfDecimalPlaces(x,y,3));
    assertTrue(doublesSameNumberOfDecimalPlaces(x,y,4));
    assertTrue(doublesSameNumberOfDecimalPlaces(x,y,5));
    assertFalse(doublesSameNumberOfDecimalPlaces(x,y,6));
}

Answer 2

A nice way using BigDecimal :

import java.math.BigDecimal;
import java.math.MathContext;
import java.math.RoundingMode;
import java.util.Scanner;

public class Equal {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        String num1;
        String num2;
        int num3;
        while (input.hasNext()) {
            // First number
            num1 = input.next();
            // Second number
            num2 = input.next();
            // Number of significant figures
            num3 = Integer.parseInt(input.next());
            MathContext mc = new MathContext(num3, RoundingMode.HALF_UP);
            BigDecimal bdNum1 = new BigDecimal(num1, mc);
            BigDecimal bdNum2 = new BigDecimal(num2, mc);
            System.out.println(bdNum1.equals(bdNum2));
        }
        input.close();
    }
}

Depending on your concrete needs you might want to play around with the RoundingMode .

Sample input:

1.2345678
1.2345679
7

Sample output:

true

Sample input:

0.123
0.124
3

Sample output:

false

Note that the behaviour might not be as expected in special cases like:

Input:

0.10000
0.1000
8

Output:

false