Java Glossary : round

Last updated 2004-06-28 by Roedy Green ©1996-2004 Canadian Mind Products

Java definitions: 0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

You are here : home : Java Glossary : R words : round.

round

To take a float or double and want the corresponding integer (possibly as a float, double, int or long) there are five basic algorithms you might use: round, ceil, floor, truncate and cover. In elementary school you learned that rounding always involves 0.5. Java and the IEEE use the term in a more general sense to describe any way a number is converted from floating point to integer.

• Round

  Numbers less that x.5 are rounded down toward zero, and those x.5 and above are rounded up to the next integer.

  long Math. round ( double );
  int Math. round ( float );
  double rint ( double );
  

  value	round
  -1.6	-2
  -1.5	-2
  -1.4	-1
  +1.4	+1
  +1.5	+2
  +1.6	+2

• Ceiling

  Numbers are always rounded up to the next integer.

  double Math.ceil( double );
  

  See the description of covered quotient division.

  value	ceil
  -1.6	-1
  -1.5	-1
  -1.4	-1
  +1.4	+2
  +1.5	+2
  +1.6	+2

• Floor

  Numbers are always rounded down to the next lowest integer.

  double Math.floor( double );
  

  See floored division.

  value	floor
  -1.6	-2
  -1.5	-2
  -1.4	-2
  +1.4	+1
  +1.5	+1
  +1.6	+1

• Truncate

  Numbers are always rounded down toward zero.

  int i = (int)d;
  

  value	truncate
  -1.6	-1
  -1.5	-1
  -1.4	-1
  +1.4	+1
  +1.5	+1
  +1.6	+1

• Cover

  Numbers are always rounded up away from zero. There is no simple function to do this.

  d<0 ? Math.floor( d ) : Math.ceil( d );
  

  value	cover
  -1.6	-2
  -1.5	-2
  -1.4	-2
  +1.4	+2
  +1.5	+2
  +1.6	+2

Rounding Gotcha

// Java normally truncates (rounds toward 0 in IEEE jargon)
double x1 = 5673892.61;
long trunc = (long)x1;
// prints 5673892
System.out.println( trunc );

// Sometimes Java appears to round, but that is an illusion
// created because doubles are only accurate to 14 or 15 figures.
double x2 = 5673892111111112.61;
long round = (long)x2;
// prints 5673892111111113
System.out.println( round );

ceil ¤ division ¤ floating point ¤ floor ¤ modulus ¤ truncate

home	Canadian Mind Products
	mindprod.com IP:[24.87.56.253]
	Your IP:[80.134.30.163]
	You are visitor number 4923.
	Please send errors, omissions and suggestions
	to improve this page to Roedy Green.
	You can get a fresh copy of this page from:	or possibly from your local J: drive mirror:
	http://mindprod.com/jgloss/round.html	J:\mindprod\jgloss\round.html