处理大数字BigInteger与BigDecimal
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package prime;import java.math.BigDecimal;import java.math.BigInteger;public class BigNumber {// 默认除法运算精度,即保留小数点多少位private static final int DEFAULT_DIV_SCALE = 10;// 这个类不能实例化private BigNumber() {}public static double add(double v1, double v2) {BigDecimal b1 = new BigDecimal(Double.toString(v1));BigDecimal b2 = new BigDecimal(Double.toString(v2));return (b1.add(b2)).doubleValue();}public static double sub(double v1, double v2) {BigDecimal b1 = new BigDecimal(Double.toString(v1));BigDecimal b2 = new BigDecimal(Double.toString(v2));return (b1.subtract(b2)).doubleValue();}public static double mul(double v1, double v2) {BigDecimal b1 = new BigDecimal(Double.toString(v1));BigDecimal b2 = new BigDecimal(Double.toString(v2));return (b1.multiply(b2)).doubleValue();}public static double div(double v1, double v2) {return div(v1, v2, DEFAULT_DIV_SCALE);}public static double div(double v1, double v2, int scale) {if (scale < 0) {System.err.println("除法精度必须大于0!");return 0;}BigDecimal b1 = new BigDecimal(Double.toString(v1));BigDecimal b2 = new BigDecimal(Double.toString(v2));return (b1.divide(b2, scale, BigDecimal.ROUND_HALF_UP)).doubleValue();}public static BigInteger getFactorial(int n) {if (n < 0) {System.err.println("n必须大于等于0!");return new BigInteger("-1");} else if (n == 0) {return new BigInteger("0");}// 将数组换成字符串后构造BigIntegerBigInteger result = new BigInteger("1");for (; n > 0; n--) {// 将数字n转换成字符串后,再构造一个BigInteger对象,与现有结果做乘法result = result.multiply(new BigInteger(new Integer(n).toString()));}return result;}public static void main(String[] args) {// 如果我们编译运行下面这个程序会看到什么?System.out.println(0.05 + 0.01);System.out.println(1.0 - 0.42);System.out.println(4.015 * 100);System.out.println(123.3 / 100);// 0.060000000000000005// 0.5800000000000001// 401.49999999999994// 1.2329999999999999// 计算阶乘,可以将n设得更大int n = 30;System.out.println("计算n的阶乘" + n + "! = " + BigNumber.getFactorial(n));// 用double构造BigDecimalBigDecimal bd1 = new BigDecimal(0.1);System.out.println("(bd1 = new BigDecimal(0.1)) = " + bd1.toString());// 用String构造BigDecimalBigDecimal bd2 = new BigDecimal("0.1");System.out.println("(bd2 = new BigDecimal('0.1')) = " + bd2.toString());BigDecimal bd3 = new BigDecimal("0.10");// equals方法比较两个BigDecimal对象是否相等,相等返回true,不等返回falseSystem.out.println("bd2.equals(bd3) = " + bd2.equals(bd3));// false// compareTo方法比较两个BigDecimal对象的大小,相等返回0,小于返回-1,大于返回1。System.out.println("bd2.compareTo(bd3) = " + bd2.compareTo(bd3));// 0// 进行精确计算System.out.println("0.05 + 0.01 = " + BigNumber.add(0.05, 0.01));System.out.println("1.0 - 0.42 = " + BigNumber.add(1.0, 0.42));System.out.println("4.015 * 100 =" + BigNumber.add(4.015, 100));System.out.println("123.3 / 100 = " + BigNumber.add(123.3, 100));}}
运行结果:
0.060000000000000005
0.5800000000000001
401.49999999999994
1.2329999999999999
计算n的阶乘30! = 265252859812191058636308
(bd1 = new BigDecimal(0.1)) = 0.100000000000000005551115
(bd2 = new BigDecimal("0.1")) = 0.1
bd2.equals(bd3) = false
bd2.compareTo(bd3) = 0
0.05 + 0.01 = 0.06
1.0 - 0.42 = 1.42
4.015 * 100 =104.015
123.3 / 100 = 223.3
源码分析:
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