MutableBigInteger的性能

我尝试使用BigInteger计算具有大精度（高达10000）的特定输入下的整数平方根的数字之和。

public class SquareRootHackerRankJarvis { static BigInteger limit; static BigInteger a; static BigInteger b; private static BigInteger squareroot(int n, BigInteger ten, BigInteger hundred, BigInteger five) { a = BigInteger.valueOf(n * 5); b = BigInteger.valueOf(5); while (b.compareTo(limit) == -1) { if (a.compareTo(b) != -1) { a = a.subtract(b); b = b.add(ten); } else { a = a.multiply(hundred); b = (b.divide(ten)).multiply(hundred).add(five); } } return b.divide(hundred); } public static void main(String[] args) { Scanner scanner = new Scanner(System.in); int N = scanner.nextInt(); int P = scanner.nextInt(); int sum = 0; int p = 1; BigInteger ten = BigInteger.valueOf(10); BigInteger hundred = BigInteger.valueOf(100); BigInteger five = BigInteger.valueOf(5); limit = ten.pow(P + 1); for (int i = 1; i <= N; i++) { if (p * p == i) { p++; continue; } BigInteger x = squareroot(i, ten, hundred, five); char[] digits = x.toString().toCharArray(); for (int j = 0; j <= P - 1; j++) { sum += Character.getNumericValue(digits[j]); } } System.out.println(sum); scanner.close(); }} 

性能非常糟糕，精度10000（P）需要花费大量时间。 我在另一篇文章中读到MutableBigInteger在BigInteger之前表现良好，因为它是可变的。因此我使用MutableBigInteger重构了代码。

 public class SquareRootHackerRankJarvisMutableBigInteger { static Object limit; static Object a; static Object b; public static void main(String[] args) throws NoSuchMethodException, SecurityException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException, ClassNotFoundException { Scanner scanner = new Scanner(System.in); int N = scanner.nextInt(); int P = scanner.nextInt(); int sum = 0; int p = 1; BigInteger tenB = BigInteger.valueOf(10); Class c = Class.forName("java.math.MutableBigInteger"); Constructor constructor = c.getDeclaredConstructor(int.class); constructor.setAccessible(true); Constructor constructor1 = c .getDeclaredConstructor(BigInteger.class); constructor1.setAccessible(true); Method add = c.getDeclaredMethod("add", new Class[] { c }); Method subtract = c.getDeclaredMethod("subtract", new Class[] { c }); Method mul = c.getDeclaredMethod("mul", new Class[] { int.class, c }); Method divide = c.getDeclaredMethod("divide", new Class[] { long.class, c }); Method compare = c.getDeclaredMethod("compare", new Class[] { c }); Method copyValue = c.getDeclaredMethod("copyValue", new Class[] { c }); add.setAccessible(true); subtract.setAccessible(true); mul.setAccessible(true); divide.setAccessible(true); compare.setAccessible(true); copyValue.setAccessible(true); Object ten = constructor.newInstance(10); Object five = constructor.newInstance(5); Object v = constructor.newInstance(0); Object sqrt = constructor.newInstance(0); limit = constructor1.newInstance(tenB.pow(P + 1)); for (int i = 1; i <= N; i++) { if (p * p == i) { p++; continue; } a = constructor.newInstance(i * 5); b = constructor.newInstance(5); while (((Integer) compare.invoke(b, limit)).intValue() == -1) { if (((Integer) compare.invoke(a, b)).intValue() != -1) { subtract.invoke(a, b); add.invoke(b, ten); } else { mul.invoke(a, 100, v); copyValue.invoke(a, v); divide.invoke(b, 10, v); mul.invoke(v, 100, b); add.invoke(b, five); } } divide.invoke(b, 100, sqrt); char[] digits = sqrt.toString().toCharArray(); for (int j = 0; j <= P - 1; j++) { sum += Character.getNumericValue(digits[j]); } } System.out.println(sum); scanner.close(); }} 

但我仍然看不到任何性能提升。任何人都可以给我任何关于MutableBigInteger与Reflection正确使用的建议吗？