print double number in java and get wrong answer [duplicate]

Question

This question already has answers here:

Double calculation producing odd result [duplicate] (3 answers)

Closed 8 years ago.

double check =0.615 * 255 -0.515 * 255 -0.100 * 255;
System.out.println(check);

why get -2.8421709430404007E-14? it should be 0.0

Answer 1

Double operation has some precision problem. Use BigDecimal operation instead of double than you will get expected result.

  //double check =0.615 * 255 + -0.515 * 255 + -0.100 * 255;
   BigDecimal check =
             (BigDecimal.valueOf(0.615).multiply(BigDecimal.valueOf(255)))
            .add(BigDecimal.valueOf( -0.515).multiply(BigDecimal.valueOf( 255)))
            .add(BigDecimal.valueOf( -0.100).multiply(BigDecimal.valueOf( 255)));

  System.out.println(check);

Result is : 0.000

Answer 2

Debugging your math:

double check0 = 0.615 * 255;
System.out.println(check0);
double check1 = -0.515 * 255;
System.out.println(check1);
double check3 = -0.100 * 255;
System.out.println(check3);
System.out.println("Result: " + (check0 + check1 + check3));

Output:

156.825
-131.32500000000002
-25.5
Result: -2.8421709430404007E-14

Remember that:

• multiplication has higher operator priority than addition in Java
• you should use BigDecimal if you want control over the rounding when performing operations with floating point numbers