System.out.println(d)
va passer par Double.toString
ce qui est une méthode assez complexe (comme on le voit dans sa documentation) et ne se comportera pas toujours comme on s'y attendrait. Il donne essentiellement la chaîne la plus courte qui détermine de façon unique d
.
Peut-être la sortie de ce programme précise ceci:
double[] tests = {
0.49999999999999990d, //output 0.4999999999999999 as expected
0.49999999999999991d, //output 0.4999999999999999
0.49999999999999992d, //output 0.49999999999999994
0.49999999999999993d, //output 0.49999999999999994
0.49999999999999994d, //output 0.49999999999999994 as expected
0.49999999999999995d, //output 0.49999999999999994
0.49999999999999996d, //output 0.49999999999999994
0.49999999999999997d, //output 0.49999999999999994
0.49999999999999998d, //output 0.5
};
String[] literals = {
"0.49999999999999990d",
"0.49999999999999991d",
"0.49999999999999992d",
"0.49999999999999993d",
"0.49999999999999994d",
"0.49999999999999995d",
"0.49999999999999996d",
"0.49999999999999997d",
"0.49999999999999998d",
};
String f = "%-25s%-65s%-25s%n";
System.out.printf(f, "Literal", "Actually represents", "Printed as");
for (int i = 0; i < tests.length; i++)
System.out.printf(f, literals[i],
new BigDecimal(tests[i]).toString(),
Double.valueOf(tests[i]));
Sortie:
Literal Actually represents Printed as
0.49999999999999990d 0.49999999999999988897769753748434595763683319091796875 0.4999999999999999
0.49999999999999991d 0.49999999999999988897769753748434595763683319091796875 0.4999999999999999
0.49999999999999992d 0.499999999999999944488848768742172978818416595458984375 0.49999999999999994
0.49999999999999993d 0.499999999999999944488848768742172978818416595458984375 0.49999999999999994
0.49999999999999994d 0.499999999999999944488848768742172978818416595458984375 0.49999999999999994
0.49999999999999995d 0.499999999999999944488848768742172978818416595458984375 0.49999999999999994
0.49999999999999996d 0.499999999999999944488848768742172978818416595458984375 0.49999999999999994
0.49999999999999997d 0.499999999999999944488848768742172978818416595458984375 0.49999999999999994
0.49999999999999998d 0.5 0.5
Comme on le voit, le littéral est parfois loin de la valeur qu'il représente en fait, ce qui signifie que Double.toString
imprime quelque chose qui peut paraître surprenant.
duplication possible de [Conserver la précision avec Double dans java] (http://stackoverflow.com/questions/322749/retain-precision-with-doubles-in-java) –