BigInteger、BigDecimal类的使用详解
我们都知道在java里边long算是存储长度比较大的了，但是如果有很大的数我们应该怎么处理呢，不用怕，java还为我们准备了一个BigInteger的类，那么这个类到底能存储多大的数呢，这个一时还真不好想，要取决于你计算机的内存大小，意味着我们的内存越大，这个类存储的位数就越大。接下来我们来看看BigInteger这个类。
BigInteger继承了Number类并且实现了Serializable ， Comparable < BigInteger >接口
首先来看他的构造函数
这个类与之对应的还有三个常量，我们来看下
接下来我们说下他常用的构造函数
比较常用的就是用字符串来直接传入
BigInteger bigInteger = new BigInteger("999999999999999999");
比较常用的成员方法有如下：
BigInteger abs() 返回大整数的绝对值
BigInteger add(BigInteger val) 返回两个大整数的和
BigInteger and(BigInteger val) 返回两个大整数的按位与的结果
BigInteger andNot(BigInteger val) 返回两个大整数与非的结果
BigInteger divide(BigInteger val) 返回两个大整数的商
double doubleValue() 返回大整数的double类型的值
float floatValue() 返回大整数的float类型的值
BigInteger gcd(BigInteger val) 返回大整数的最大公约数
int intValue() 返回大整数的整型值
long longValue() 返回大整数的long型值
BigInteger max(BigInteger val) 返回两个大整数的最大者
BigInteger min(BigInteger val) 返回两个大整数的最小者
BigInteger mod(BigInteger val) 用当前大整数对val求模
BigInteger multiply(BigInteger val) 返回两个大整数的积
BigInteger negate() 返回当前大整数的相反数
BigInteger not() 返回当前大整数的非
BigInteger or(BigInteger val) 返回两个大整数的按位或
BigInteger pow(int exponent) 返回当前大整数的exponent次方
BigInteger remainder(BigInteger val) 返回当前大整数除以val的余数
BigInteger leftShift(int n) 将当前大整数左移n位后返回
BigInteger rightShift(int n) 将当前大整数右移n位后返回
BigInteger subtract(BigInteger val)返回两个大整数相减的结果
byte[] toByteArray(BigInteger val)将大整数转换成二进制反码保存在byte数组中
String toString() 将当前大整数转换成十进制的字符串形式
BigInteger xor(BigInteger val) 返回两个大整数的异或我们来看几个测试
public static void main(String[] args) {
BigInteger b1 = new BigInteger("999999999999999999999");
BigInteger b2 = new BigInteger("888888888888888888888");
//加法
System.out.println(b1.subtract(b2));
//减法
System.out.println(b1.add(b2));
//乘法
System.out.println(b1.multiply(b2));
//除法
System.out.println(b1.divide(b2));
//取余
System.out.println(b1.remainder(b2));
//除并取余
BigInteger[] bbs = b1.divideAndRemainder(b2);
System.out.println(bbs[0]+"--"+bbs[1]);
}
程序的运行结果如下：
111111111111111111111
1888888888888888888887
888888888888888888887111111111111111111112
1
111111111111111111111
1--111111111111111111111
接下来我带大家看下BigInteger底层的源码
这个this是什么东西呢，我们继续往下看
/**
* Translates the String representation of a BigInteger in the
* specified radix into a BigInteger. The String representation
* consists of an optional minus or plus sign followed by a
* sequence of one or more digits in the specified radix. The
* character-to-digit mapping is provided by {@code
* Character.digit}. The String may not contain any extraneous
* characters (whitespace, for example).
*
* @param val String representation of BigInteger.
* @param radix radix to be used in interpreting {@code val}.
* @throws NumberFormatException {@code val} is not a valid representation
* of a BigInteger in the specified radix, or {@code radix} is
* outside the range from {@link Character#MIN_RADIX} to
* {@link Character#MAX_RADIX}, inclusive.
* @see Character#digit
*/
public BigInteger(String val, int radix) { //首先这里有一个基数因子 是指当前是多少进制的
int cursor = 0, numDigits;
final int len = val.length(); //这个地方会获取到当前传入字符串的总长度
//这里有两个常量 MIN_RADIX = 2 , MAX_RADIX = 36
if (radix < Character.MIN_RADIX || radix > Character.MAX_RADIX)
throw new NumberFormatException("Radix out of range");
if (len == 0)
throw new NumberFormatException("Zero length BigInteger");
// Check for at most one leading sign
//这里会检测传入的字符串是否是纯数字
int sign = 1;
int index1 = val.lastIndexOf('-');
int index2 = val.lastIndexOf('+');
if (index1 >= 0) {
if (index1 != 0 || index2 >= 0) {
throw new NumberFormatException("Illegal embedded sign character");
}
sign = -1;
cursor = 1;
} else if (index2 >= 0) {
if (index2 != 0) {
throw new NumberFormatException("Illegal embedded sign character");
}
cursor = 1;
}
if (cursor == len)
throw new NumberFormatException("Zero length BigInteger");
// Skip leading zeros and compute number of digits in magnitude
while (cursor < len &&
Character.digit(val.charAt(cursor), radix) == 0) {
cursor++;
}
if (cursor == len) {
signum = 0;
mag = ZERO.mag;
return;
}
numDigits = len - cursor;
signum = sign;
// Pre-allocate array of expected size. May be too large but can
// never be too small. Typically exact.
long numBits = ((numDigits * bitsPerDigit[radix]) >>> 10) + 1;
if (numBits + 31 >= (1L << 32)) {
reportOverflow();
}
int numWords = (int) (numBits + 31) >>> 5;
int[] magnitude = new int[numWords];
// Process first (potentially short) digit group
int firstGroupLen = numDigits % digitsPerInt[radix];
if (firstGroupLen == 0)
firstGroupLen = digitsPerInt[radix];
String group = val.substring(cursor, cursor += firstGroupLen);
magnitude[numWords - 1] = Integer.parseInt(group, radix);
if (magnitude[numWords - 1] < 0)
throw new NumberFormatException("Illegal digit");
// Process remaining digit groups
int superRadix = intRadix[radix];
int groupVal = 0;
while (cursor < len) {
group = val.substring(cursor, cursor += digitsPerInt[radix]);
groupVal = Integer.parseInt(group, radix);
if (groupVal < 0)
throw new NumberFormatException("Illegal digit");
destructiveMulAdd(magnitude, superRadix, groupVal);
}
// Required for cases where the array was overallocated.
mag = trustedStripLeadingZeroInts(magnitude);
if (mag.length >= MAX_MAG_LENGTH) {
checkRange();
}
}看了以上的代码，相信你对BigInteger大概已经有了一个新的认识。
以上内容部分来自网络，与BigInteger对应的还有一个BigDecimal，可以存小数，与BigInteger的用法一模一样，有问题可以在下面评论，技术问题可以私聊我。
