最简单的方法可能是使用反复试验.

public static String toFraction(double d, int factor) {

StringBuilder sb = new StringBuilder();

if (d < 0) {

sb.append('-');

d = -d;

}

long l = (long) d;

if (l != 0) sb.append(l);

d -= l;

double error = Math.abs(d);

int bestDenominator = 1;

for(int i=2;i<=factor;i++) {

double error2 = Math.abs(d - (double) Math.round(d * i) / i);

if (error2 < error) {

error = error2;

bestDenominator = i;

}

}

if (bestDenominator > 1)

sb.append(' ').append(Math.round(d * bestDenominator)).append('/') .append(bestDenominator);

return sb.toString();

}

public static void main(String... args) {

System.out.println(toFraction(1.3333, 1000));

System.out.println(toFraction(1.1428, 1000));

for(int i=1;i<100000000;i*=10) {

System.out.println("PI "+i+": "+toFraction(3.1415926535897932385, i));

}

}

版画

1 1/3

1 1/7

PI 1: 3

PI 10: 3 1/7

PI 100: 3 14/99

PI 1000: 3 16/113

PI 10000: 3 16/113

PI 100000: 3 14093/99532

PI 1000000: 3 140914/995207

PI 10000000: 3 244252/1725033