Java5:BigInteger、BigDecimal详解

从Java4到Java5,Java对BigInteger、BigDecimal两个类功能一直再做扩展与改进。主要原因是这两个数据类型很重要,在高精度的计算中全靠这两个数据类型了。BigInteger和BigDecimal分别表示任意精度的整数与浮点数。
 
本文中不在追溯各个版本的变化,只看Java5中两个类的使用。
 
一、java.math.BigInteger
 
不可变的任意精度的整数。 此类的用法比较简单些,也不存在舍入等操作。
 
package lavasoft;

import java.math.BigInteger;
import java.util.Random;

/**
* 测试BigInteger
*
* @author leizhimin 2009-11-17 12:49:41
*/

public class TestBigInteger {
        public static void main(String[] args) {
                System.out.println("-------------------构造BigInteger---------------------");
                //通过byte数组来创建BigInteger
                BigInteger bi1 = new BigInteger(new byte[]{1, 1});
                System.out.println("bi1=" + bi1.toString());
                //创建带符号的BigInteger
                BigInteger bi2 = new BigInteger(-1, new byte[]{1, 1});
                System.out.println("bi2=" + bi2.toString());
                //创建带符号的BigInteger随机数
                BigInteger bi3 = new BigInteger(128, 20, new Random());
                System.out.println("bi3=" + bi3.toString());
                //通过10进制字符串创建带符号的BigInteger
                BigInteger bi4 = new BigInteger("12342342342342123423423412341");
                System.out.println("bi4=" + bi4.toString());
                //通过10进制字符串创建带符号的BigInteger
                BigInteger bi5 = new BigInteger("88888888888888888888888888888", Character.digit('a', 33));
                System.out.println("bi5=" + bi5.toString());
                System.out.println("BigInteger的常量:");
                System.out.println("BigInteger.ZERO=" + BigInteger.ZERO);
                System.out.println("BigInteger.ONE=" + BigInteger.ONE);
                System.out.println("BigInteger.TEN=" + BigInteger.TEN);

                System.out.println("-------------------使用BigInteger---------------------");
                System.out.println("bi1的相反数=" + bi1.negate());
                System.out.println("bi1的相反数=" + bi1.negate());
                System.out.println("bi1+bi2=" + bi1.add(bi2));
                System.out.println("bi1-bi2=" + bi1.subtract(bi2));
                System.out.println("bi1*bi2=" + bi1.multiply(bi2));
                System.out.println("bi1/bi2=" + bi1.divide(bi2));
                System.out.println("bi1的10次方=" + bi1.pow(10));
                System.out.println("bi1的10次方=" + bi1.pow(1));
                BigInteger[] bx = bi4.divideAndRemainder(bi1);
                System.out.println(">>>:bx[0]=" + bx[0] + ",bx[1]=" + bx[1]);
                System.out.println("bi2的绝对值=" + bi2.abs());
        }
}
 
运行结果:
-------------------构造BigInteger---------------------
bi1=257
bi2=-257
bi3=175952079487573456985958549621373190227
bi4=12342342342342123423423412341
bi5=88888888888888888888888888888
BigInteger的常量:
BigInteger.ZERO=0
BigInteger.ONE=1
BigInteger.TEN=10
-------------------使用BigInteger---------------------
bi1的相反数=-257
bi1的相反数=-257
bi1+bi2=0
bi1-bi2=514
bi1*bi2=-66049
bi1/bi2=-1
bi1的10次方=1256988294225653106805249
bi1的10次方=257
>>>:bx[0]=48024678374872075577523005,bx[1]=56
bi2的绝对值=257

Process finished with exit code 0
 
二、java.math.BigDecimal
 
不可变的、任意精度的有符号十进制数。与之相关的还有两个类:
java.math.MathContext:
该对象是封装上下文设置的不可变对象,它描述数字运算符的某些规则,如数据的精度,舍入方式等。
java.math.RoundingMode:这是一种枚举类型,定义了很多常用的数据舍入方式。
 
这个类用起来还是很比较复杂的,原因在于舍入模式,数据运算规则太多太多,不是数学专业出身的人看着中文API都难以理解,这些规则在实际中使用的时候在翻阅都来得及。
 
package lavasoft;

import java.math.BigDecimal;
import java.math.MathContext;
import java.math.RoundingMode;

/**
* 测试BigDecimal
*
* @author leizhimin 2009-11-17 12:50:03
*/

public class TestBigDecimal {

        public static void main(String[] args) {
                System.out.println("------------构造BigDecimal-------------");
                //从char[]数组来创建BigDecimal
                BigDecimal bd1 = new BigDecimal("123456789.123456888".toCharArray(), 4, 12);
                System.out.println("bd1=" + bd1);
                //从char[]数组来创建BigDecimal
                BigDecimal bd2 = new BigDecimal("123456789.123456111133333213".toCharArray(), 4, 18, MathContext.DECIMAL128);
                System.out.println("bd2=" + bd2);
                //从字符串创建BigDecimal
                BigDecimal bd3 = new BigDecimal("123456789.123456111133333213");
                System.out.println("bd3=" + bd3);
                //从字符串创建BigDecimal,3是有效数字个数
                BigDecimal bd4 = new BigDecimal("88.456", new MathContext(3, RoundingMode.UP));
                System.out.println("bd4=" + bd4);
                System.out.println("------------使用BigDecimal-------------");
                System.out.println("bd1+bd2=" + bd1.add(bd2));
                System.out.println("bd1+bd2=" + bd1.add(bd2, new MathContext(24, RoundingMode.UP)));
                System.out.println("bd1-bd2=" + bd1.subtract(bd2).toPlainString());
                System.out.println("bd1-bd2=" + bd1.subtract(bd2, new MathContext(24, RoundingMode.UP)).toPlainString());
                System.out.println("bd1*bd2=" + bd1.multiply(bd2));
                System.out.println("bd1*bd2=" + bd1.multiply(bd2, new MathContext(24, RoundingMode.UP)));
                System.out.println("bd1/bd4=" + bd1.divideToIntegralValue(bd4));
                System.out.println("bd1/bd4=" + bd1.divideToIntegralValue(bd4, new MathContext(24, RoundingMode.UP)));
                System.out.println("bd1末位数据精度=" + bd1.ulp());
                System.out.println("bd2末位数据精度=" + bd2.ulp());
                System.out.println("bd2末位数据精度=" + bd2.ulp().toPlainString());
                System.out.println("bd1符号:" + bd1.signum());
                System.out.println("bd4的标度:" + bd4.scale());
        }
}
 
运行结果:
------------构造BigDecimal-------------
bd1=56789.123456
bd2=56789.123456111133
bd3=123456789.123456111133333213
bd4=88.5
------------使用BigDecimal-------------
bd1+bd2=113578.246912111133
bd1+bd2=113578.246912111133
bd1-bd2=-0.000000111133
bd1-bd2=-0.000000111133
bd1*bd2=3225004542.907120529593035648
bd1*bd2=3225004542.90712052959304
bd1/bd4=641.00000
bd1/bd4=641.00000
bd1末位数据精度=0.000001
bd2末位数据精度=1E-12
bd2末位数据精度=0.000000000001
bd1符号:1
bd4的标度:1

Process finished with exit code 0
 
最后回顾下本文所涉及的API范围:
 
java.math包:
掌握了构造方式,和常见的数学运算,在开发中一般够用了。