大整型对象(BigInteger)
BigInteger和BigDecimal相比，大部分的功能是相同的，主要的差异为BigInteger仅仅表示大整数的封装，而不能表示浮点数，与此同时，BigInteger还提供了大量的位操作运算，这个和C++中的BitSet非常类似。如果我们的在应用中只是需要大整数，那么应该首先该类，而不是BigDecimal，如果我们的应用逻辑中有多于64种状态(long表示64bits)的情况，可以考虑用BigInteger的位操作功能。
①基本的数学运算和数学函数应用：
1 public static void main(String args[]) {
2 BigInteger bi1 = new BigInteger("1234567890123456890");
3 BigInteger bi2 = BigInteger.valueOf(123L);
4 System.out.printf("bi1 = %s after added\n",bi1.add(bi2));
5 System.out.printf("bi1 = %s after multiply\n",bi1.multiply(bi2));
6 System.out.printf("bi1 = %s after subtract\n",bi1.subtract(bi2));
7 System.out.printf("bi1 = %s after divide\n",bi1.divide(bi2));
8 System.out.printf("bi1 = %s after negate\n",bi1.negate());
9 int exponent = 2;
10 System.out.printf("bi1 = %s after pow\n",bi1.pow(exponent));
11 }
12 /* 输出结果如下：
13 bi1 = 1234567890123457013 after added
14 bi1 = 151851850485185197470 after multiply
15 bi1 = 1234567890123456767 after subtract
16 bi1 = 10037137318076885 after divide
17 bi1 = -1234567890123456890 after negate
18 bi1 = 1524157875323883924401765803688472100 after pow
19 */
②将BigInteger的值转换为各种进制的字符串表示：
1 public static void main(String args[]) {
2 BigInteger number = new BigInteger("2008");
3 System.out.println("Number = " + number);
4 System.out.println("Binary = " + number.toString(2));
5 System.out.println("Octal = " + number.toString(8));
6 System.out.println("Hexadecimal = " + number.toString(16));
7 number = new BigInteger("FF", 16);
8 System.out.println("Number = " + number);
9 System.out.println("Number = " + number.toString(16));
10 }
11 /* 输出结果如下：
12 Number = 2008
13 Binary = 11111011000
14 Octal = 3730
15 Hexadecimal = 7d8
16 Number = 255
17 Number = ff
18 */
③ 从字符串构造各种进制的BigInteger对象：
1 public static void main(String args[]) {
2 BigInteger bi = new BigInteger("120ff0", 16);
3 Integer ii = Integer.valueOf("120ff0", 16);
4 if (bi.intValue() == ii.intValue())
5 System.out.println("bi.intValue == ii.intValue");
6 System.out.println("int i = " + bi.intValue());
7
8 BigInteger bi2 = new BigInteger("100100100111111110000", 2);
9 System.out.println(bi2.intValue());
10 }
11 /* 输出结果如下：
12 bi.intValue == ii.intValue
13 int i = 1183728
14 1200112
15 */
④ 位操作：
1 public static void main(String args[]) {
2 byte[] bytes = new byte[] { 0x1, 0x00, 0x00 };
3 BigInteger bi = new BigInteger(bytes);
4 //相当于 & (~)的位运算。
5 System.out.println("andNot = " + bi.andNot(bi));
6 //相当于 | 的位运算
7 BigInteger bi2 = new BigInteger(bytes);
8 System.out.println("or = " + bi2.or(bi2));
9 //相当于 ~ 的位运算
10 BigInteger bi3 = new BigInteger(bytes);
11 System.out.println("not = " + bi3.not());
12 //相当于 & 的位运算
13 BigInteger bi4 = new BigInteger(bytes);
14 System.out.println("and = " + bi4.and(bi4));
15 //相当于 ^ 的位运算
16 BigInteger bi5 = new BigInteger(bytes);
17 System.out.println("xor = " + bi5.xor(bi5));
18 }
19 /* 输出结果如下：
20 andNot = 0
21 or = 65536
22 not = -65537
23 and = 65536
24 xor = 0
25 */
2 byte[] bytes = new byte[] { 0x1, 0x00, 0x00 };
3 BigInteger bi = new BigInteger(bytes);
4 //相当于 & (~)的位运算。
5 System.out.println("andNot = " + bi.andNot(bi));
6 //相当于 | 的位运算
7 BigInteger bi2 = new BigInteger(bytes);
8 System.out.println("or = " + bi2.or(bi2));
9 //相当于 ~ 的位运算
10 BigInteger bi3 = new BigInteger(bytes);
11 System.out.println("not = " + bi3.not());
12 //相当于 & 的位运算
13 BigInteger bi4 = new BigInteger(bytes);
14 System.out.println("and = " + bi4.and(bi4));
15 //相当于 ^ 的位运算
16 BigInteger bi5 = new BigInteger(bytes);
17 System.out.println("xor = " + bi5.xor(bi5));
18 }
19 /* 输出结果如下：
20 andNot = 0
21 or = 65536
22 not = -65537
23 and = 65536
24 xor = 0
25 */
