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Math.round() method

shetal bansal
Ranch Hand

Joined: May 09, 2005
Posts: 63
What is the output of following

Answer is :

Round f4 is -5
Round f5 is 6
Round f6 is -5
Round f7 is 5

How r the value of f6 and f7 getting calculated??
marc weber

Joined: Aug 31, 2004
Posts: 11343

Math.round(double d)...

"Returns the closest long to the argument. The result is rounded to an integer by adding 1/2, taking the floor of the result, and casting the result to type long."

"We're kind of on the level of crossword puzzle writers... And no one ever goes to them and gives them an award." ~Joe Strummer
Abdulla Mamuwala
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Joined: Jan 09, 2004
Posts: 225
I am not sure, but this could be the way you do it.
First add 0.5 to the argument and than perform a Math.floor() on it.

Here f6=-5.49
-5.49 + 0.5 = -4.99
Now, we perform a Math.floor() on -4.99 giving -5, because -5 is less than -4.

Similarly f7=5.49
5.49 + 0.5 = 5.99
Now, we perform a Math.floor() on 5.99 giving 5, because 5 is less than 6.

Math.round() returns integer closest to the argument in the case above because the arguments are of type float.
[ June 17, 2005: Message edited by: Abdulla Mamuwala ]
Edwin Dalorzo
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Joined: Dec 31, 2004
Posts: 961
For the SCJP exam I think it is important to recognize the next things

  • double Math.floor(double a): receives a double and returns a double
  • double Math.ceil(double a) : receives a double and returns a double
  • int Math.round(float a): receives a float returns a integer
  • long Math.round(double a): receives a double returns a long

  • It is important to recognize that in the next output

    Now, rouund might behave different for positive and negative numbers.


    Be careful with that, because that is a probable question in the exam.
    Rick O'Shay
    Ranch Hand

    Joined: Sep 19, 2004
    Posts: 531
    float f6 = -5.49f;
    float f7 = 5.49f;

    Rounds off to the nearest integer: -5 and 5 respectively.

    Given -5.5 and 5.5 you need a rounding rule since there are two "nearest" integers. They decided to round up: -5, 6 respectively. In other words if smack dab in the middle add 0.5.
    shetal bansal
    Ranch Hand

    Joined: May 09, 2005
    Posts: 63
    Thanxs a lot for the wonderful replies!!
    I agree. Here's the link:
    subject: Math.round() method
    It's not a secret anymore!