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Java Forum / First Aid / January 2007altenatives for double is mathematical integer
Hi, Can anyone show me alteratives to the following for finding if a given Java double is an mathematical integer? Thanks, Jeff Higgins public class Test_Increment { public static void main(String[] args) { double d = Double.parseDouble(args[0]); System.out.println((d-Math.ceil(d))==0); } } Hi, > Hi, > Can anyone show me alteratives to the [quoted text clipped - 10 lines] > } > } Well, to answer your question, there might be other solutions like: d==(int)d You could encapsulate/refactor this test to a "utility method" and not care about *how* the test works exactly. But your question shows that you might have a more general problem in your application. Ever tried something like this?: double d = 0.1; double sum = 0; for (int i = 0; i < 10; i++) { sum = sum + d; } System.out.println(sum); System.out.println(sum == 1.0); // false!!! Perhaps, the class "BigDecimal" might be a good idea for you! Ciao, Ingo > Hi, > [quoted text clipped - 16 lines] > > d==(int)d That answers a different question, whether the double is exactly equal to some int. It will reject many doubles that are mathematical integers, but outside the int range. The original question has several subtle issues, such as making sure the infinities are rejected, and the posted code looks correct to me. Why look for alternatives? Patricia >> Hi, >>> Hi, [quoted text clipped - 23 lines] > > Patricia I think the simplest and most effective way around this is simply... System.out.println( 0 == d % 1 ? "Is Integer" : "Is Double" );  Signature- Stefan Z Camilleri - www.szc001.com > The original question has several subtle issues, such as making sure the > infinities are rejected, and the posted code looks correct to me. Why > look for alternatives? I probably wasn't looking for alternatives as much as hoping to understand the issues. I hadn't accounted for infinities and NAN plus further testing showed that d-Math.ceil(d))==0 doesn't work for at least Double.MIN_VALUE. Thanks. JH > Patricia > Hi, > Can anyone show me alteratives to the [quoted text clipped - 10 lines] > } > } Thanks Ingo,Patricia,Stefan. Appreciate the response. public class Test { public static void main(String[] args) { double zero = 0.0; double one = 1.0; double nOne = -1.0; double pInt = Integer.MAX_VALUE + 1; double nInt = Integer.MIN_VALUE - 1; double pDbl = Integer.MAX_VALUE + 1024.3; double nDbl = Integer.MIN_VALUE - 1024.3; double nan = Double.NaN; double pInf = Double.POSITIVE_INFINITY; double nInf = Double.NEGATIVE_INFINITY; double max = Double.MAX_VALUE; double min = Double.MIN_VALUE; double nrml = Double.MIN_NORMAL; double[] a = {zero,one,nOne,pInt,nInt,pDbl, nDbl,nan,pInf,nInf,max,min,nrml}; System.out.println("//d-Math.ceil(d)==0"); for(int i=0;i<a.length;i++){ if(a[i]!=0) System.out.print((a[i]-Math.ceil(a[i]))==0); System.out.println(" " + Double.valueOf(a[i]).toString()); } System.out.println("\n//d==(int)d"); for(int i=0;i<a.length;i++){ if(a[i]!=0) System.out.print(a[i]==(int)a[i]); System.out.println(" " + Double.valueOf(a[i]).toString()); } System.out.println("\n//0==d%1"); for(int i=0;i<a.length;i++){ if(a[i]!=0) System.out.print(0 == a[1] % 1 ); System.out.println(" " + Double.valueOf(a[i]).toString()); } } } //d-Math.ceil(d)==0 0.0 true 1.0 true -1.0 true -2.147483648E9 true 2.147483647E9 false 2.1474846713E9 false -2.1474846723E9 false NaN false Infinity false -Infinity true 1.7976931348623157E308 false 4.9E-324 false 2.2250738585072014E-308 //d==(int)d 0.0 true 1.0 true -1.0 true -2.147483648E9 true 2.147483647E9 false 2.1474846713E9 false -2.1474846723E9 false NaN false Infinity false -Infinity false 1.7976931348623157E308 false 4.9E-324 false 2.2250738585072014E-308 //0==d%1 0.0 true 1.0 true -1.0 true -2.147483648E9 true 2.147483647E9 true 2.1474846713E9 true -2.1474846723E9 true NaN true Infinity true -Infinity true 1.7976931348623157E308 true 4.9E-324 true 2.2250738585072014E-308 Correction: I botched the above test. Sorry, especially Stefan. System.out.print(0==a[1]%1 Should be: System.out.print(0==a[i]%1 Thanks. Jeff Higgins public class Test { public static void main(String[] args) { double zero = 0.0; double one = 1.0; double nOne = -1.0; double pInt = Integer.MAX_VALUE + 1; double nInt = Integer.MIN_VALUE - 1; double pDbl = Integer.MAX_VALUE + 1024.3; double nDbl = Integer.MIN_VALUE - 1024.3; double nan = Double.NaN; double pInf = Double.POSITIVE_INFINITY; double nInf = Double.NEGATIVE_INFINITY; double max = Double.MAX_VALUE; double min = Double.MIN_VALUE; double nrml = Double.MIN_NORMAL; double[] a = {zero,one,nOne,pInt,nInt,pDbl, nDbl,nan,pInf,nInf,max,min,nrml}; System.out.println("//d-Math.ceil(d)==0"); for(int i=0;i<a.length;i++){ if(a[i]!=0) System.out.print((a[i]-Math.ceil(a[i]))==0); System.out.println(" " + Double.valueOf(a[i]).toString()); } System.out.println("\n//d==(int)d"); for(int i=0;i<a.length;i++){ if(a[i]!=0) System.out.print(a[i]==(int)a[i]); System.out.println(" " + Double.valueOf(a[i]).toString()); } System.out.println("\n//0==d%1"); for(int i=0;i<a.length;i++){ if(a[i]!=0) System.out.print(0 == a[i] % 1 ); System.out.println(" " + Double.valueOf(a[i]).toString()); } } } //d-Math.ceil(d)==0 0.0 true 1.0 true -1.0 true -2.147483648E9 true 2.147483647E9 false 2.1474846713E9 false -2.1474846723E9 false NaN false Infinity false -Infinity true 1.7976931348623157E308 false 4.9E-324 false 2.2250738585072014E-308 //d==(int)d 0.0 true 1.0 true -1.0 true -2.147483648E9 true 2.147483647E9 false 2.1474846713E9 false -2.1474846723E9 false NaN false Infinity false -Infinity false 1.7976931348623157E308 false 4.9E-324 false 2.2250738585072014E-308 //0==d%1 0.0 true 1.0 true -1.0 true -2.147483648E9 true 2.147483647E9 false 2.1474846713E9 false -2.1474846723E9 false NaN false Infinity false -Infinity true 1.7976931348623157E308 false 4.9E-324 false 2.2250738585072014E-308 Free MagazinesGet these publications absolutely FREE for up to 12 months. 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