Multiplying doubles in java?

Question

I'm trying to multiply the same double (square it) but the number comes out wrong. When i display the double by itself the number is correct but when i multiply it by itself it comes up with the wrong number. I already tried using the math.pow function and got the same result.

    Double height=Double.parseDouble(myPrefs.getString("Heightent",""))*.0254;
    Double bmi = (height*height);
    dbmi.setText(bmi.toString());

Height is entered in a different activity in inches. When i display height in a text box it comes out to be the right number. For example, Heightent entered is 74 and 1.8796 is displayed when i put height in a textview. Butwhen I use the code above the number 16 is displayed in TextView dbmi. Any help?

can try hTemp = height.doubleValue(); Double bmi = (hTemp *hTemp ); — Dheeresh Singh, Jun 15 '12 at 12:15
Is there a specific reason, why you are using the wrapper classes? — Kirill Rakhman, Jun 15 '12 at 12:25
using what you said 'height = 74 * .0254' and now squaring the height my output is 3.532? — David Kroukamp, Jun 15 '12 at 12:25
I'm not able toString with a primitive type. Is there an easier way? — user357032, Jun 15 '12 at 12:28
It should be 3.532 but somehow it comes out as 16 in the program. — user357032, Jun 15 '12 at 12:37
By putting Double.parseDouble(myPrefs.getString("Heightent",""))*.0254 in parentheses it fixed the problem. — user357032, Jun 15 '12 at 12:45

score 3 · Accepted Answer · edited May 23 '17 at 11:44

3

Check out this great post by Stephen C.

https://stackoverflow.com/a/5385202/1214163

It should provide everything you need. He suggests that if you need to work with big numbers that you use the BigDecimal class

edited May 23 '17 at 11:44

Community

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answered Jun 15 '12 at 12:23

Deepend

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BigDecimal is a great class. I feel its harder to do multiplication with it though but that might come from my inexperience with the class. By putting Double.parseDouble(myPrefs.getString("Heightent",""))*.0254 in parentheses it fixed the problem. I'm going to accept your answer though because BigDecimal is a great class to use and be familiar with. – user357032 Jun 15 '12 at 12:48

score 1 · Answer 2 · answered Jun 15 '12 at 12:39

I tried both

    Double height=Double.parseDouble("74")*.0254;
    Double bmi = (height*height);
    System.out.println("first " + bmi);


      height=Double.parseDouble("74");
      double temp = height.doubleValue()*.0254;
      bmi = (temp*temp);
      System.out.println("Second " + bmi);

and on Calc

and got same every where..... enter image description here

Multiplying doubles in java?

2 Answers2