Math.round() method

[shetal bansal]

What is the output of following

{ 
float f4 = -5.5f; 
float f5 = 5.5f; 
float f6 = -5.49f; 
float f7 = 5.49f; 
System.out.println("Round f4 is " + Math.round(f4)); 
System.out.println("Round f5 is " + Math.round(f5)); 
System.out.println("Round f6 is " + Math.round(f6)); 
System.out.println("Round f7 is " + Math.round(f7)); 
}  

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]

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."

http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Math.html

[Abdulla Mamuwala]

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]

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

System.out.println(Math.floor(3.5)); //output 3.0
System.out.println(Math.round(3.5)); //output 4 (not 4.0)

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

Math.floor(3.5); //output 3.0
Math.ceil(3.5); //output 4.0
Math.round(3.5); //output 4

However:

Math.floor(-3.5); //output -4.0
Math.ceil(-3.5);  //output -3.0
Math.round(-3.5); //output -3
Math.round(-3.51); //output -4

Be careful with that, because that is a probable question in the exam.

[Rick O'Shay]

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]

Thanxs a lot for the wonderful replies!!