Math类
Java 的 Math 包含了用于执行基本数学运算的属性和方法，如初等指数、对数、平方根和三角函数。Math 的方法都被定义为 static 形式，通过 Math 类可以在主函数中直接调用。
Math类中有两个静态常量：E和PI
System.out.println(Math.E);
System.out.println(Math.PI);
输出
2.718281828459045
3.141592653589793
Math类的常用方法
| 方法名 | 描述 |
|---|---|
| public static long abs(double a) | 返回a的绝对值 |
| public static double max(double a, double b) | 返回a，b的最大值 |
| public static double min(double a, double b) | 返回a，b的最小值 |
| public static double random() | 产生一个0到1之间的随机数（不包括0和1） |
| public static double pow(double a, double b) | 返回a的b次幂 |
| public static double sqrt(double a) | 返回a的平方根 |
| public static double log(double a) | 返回a的以自然数e为底的对数 |
| public static double sin(double a) | 返回正弦值 |
| public static double asin(double a) | 返回反正弦值 |
| public static double cos(double a) | 返回余弦值 |
| public static double acos(double a) | 返回反余弦值 |
| public static double tan(double a) | 返回正切值 |
| public static double atan(double a) | 返回反正切值 |
| public static int ceil(double a) | 返回大于等于( >= )给定参数的的最小整数 |
| public static int ceil(float a) | 返回大于等于( >= )给定参数的的最小整数 |
| public static int floor() | 返回小于等于（<=）给定参数的最大整数 |
| public static double rint() | 返回与参数最接近的整数。返回类型为double |
| round() | 它表示四舍五入，算法为 Math.floor(x+0.5)，即将原来的数字加上 0.5 后再向下取整，所以，Math.round(11.5) 的结果为12，Math.round(-11.5) 的结果为-11。 |
| public static double exp(double d) | 返回自然数e的d次方根 |
| public static double toDegrees(double d) | 将弧度转化为角度 |
| public static double toRadians(double d) | 将角度转换为弧度 |
package Liu;
public class ArrayMethodDemo1 {
public static void main(String[] args) {
double number = 99;
double PI = Math.PI;
double E = Math.E;
System.out.println("PI等于：" + PI);
System.out.println("E等于：" + E);
System.out.println("PI和E中最大的是：" + Math.max(PI, E));
System.out.println("小于等于E的最大整数为：" + Math.floor(E));
System.out.println("以10为底的PI的对数为：" + Math.log10(PI));
System.out.println("E的PI次幂为：" + Math.pow(E, PI));
System.out.println("将PI转换成角度为：" + Math.toDegrees(PI));
}
}
输出
PI等于：3.141592653589793
E等于：2.718281828459045
PI和E中最大的是：3.141592653589793
小于等于E的最大整数为：2.0
以10为底的PI的对数为：0.49714987269413385
E的PI次幂为：23.140692632779263
将PI转换成角度为：180.0
NumberFormat类
有时我们还可能需要将数字结果进行必要的格式化，可以使用Java.text包中的NumberFormat类。
NumberFormat对象的实例化：public static final NumberFormat getInstance()
该对象调用public final String format(double b)来格式化数字b
该类中有四种常用方法格式化字符串输出设置
public void setMaximumFractionDigits(int newValue);//设置小数部分最大位数
public void setMinimumFractionDigits(int newValue);//设置小数部分最小位数
public void setMaximumIntegerDigits(int newValue);//设置整数部分最大位数
public void setMinimumIntegerDigits(int newValue);//设置整数部分最小位数
下面来一个例子
package Liu;
import java.text.NumberFormat;
public class ArrayMethodDemo1 {
public static void main(String[] args) {
double a = 3.1415926;
NumberFormat aFormat = NumberFormat.getInstance(); //实例化一个NumberFormat对象
//设置小数部分最小位数为10位
aFormat.setMinimumFractionDigits(10);
//设置整数部分最小位数为3位
aFormat.setMinimumIntegerDigits(3);
//格式化数字a
String s = aFormat.format(a);
//输出字符串s
System.out.println(s);
}
}
输出
003.1415926000
BigInteger类
不可变的任意精度的整数。所有操作中，都以二进制补码形式表示 BigInteger（如 Java 的基本整数类型）。BigInteger 提供所有 Java 的基本整数操作符的对应物，并提供 java.lang.Math 的所有相关方法。另外，BigInteger 还提供以下运算：模算术、GCD 计算、质数测试、素数生成、位操作以及一些其他操作。
BigInteger类的构造方法
public BigInteger(String VAL)构造一个十进制的BigInteger对象，该构造方法可以发生NumberFormatException异常，
也就是说，字符串参数VAL中如果含有非数字字符就会发生NumberFormatException异常。
主要有这几类构造方法。
最基本的就是public BigInteger(String VAL)，构造一个十进制的BigInteger对象。不多解释，官方文档：
BigInteger类的成员方法
| Method and Type | and Description |
|---|---|
| BigInteger abs() | Returns a BigInteger whose value is the absolute value of thisBigInteger. |
| BigInteger add(BigInteger val) | Returns a BigInteger whose value is (this + val). |
| BigInteger and(BigInteger val) | Returns a BigInteger whose value is (this & val). |
| BigInteger andNot(BigInteger val) | Returns a BigInteger whose value is (this & ~val). |
| int bitCount() | Returns the number of bits in the two’s complement representationof this BigInteger that differ from its sign bit. |
| int bitLength() | Returns the number of bits in the minimal two’s-complementrepresentation of this BigInteger, excluding a sign bit. |
| byte byteValueExact() | Converts this BigInteger to a byte, checkingfor lost information. |
| BigInteger clearBit(int n) | Returns a BigInteger whose value is equivalent to this BigIntegerwith the designated bit cleared. |
| int compareTo(BigInteger val) | Compares this BigInteger with the specified BigInteger,return 0,1,-1. |
| BigInteger divide(BigInteger val) | Returns a BigInteger whose value is (this / val). |
| BigInteger[] divideAndRemainder(BigInteger val) | Returns an array of two BigIntegers containing (this / val)followed by (this % val). |
| double doubleValue() | Converts this BigInteger to a double. |
| boolean equals(Object x) | Compares this BigInteger with the specified Object for equality. |
| float floatValue() | Converts this BigInteger to a float. |
| BigInteger gcd(BigInteger val) | Returns a BigInteger whose value is the greatest common divisor of abs(this) and abs(val). |
| int hashCode() | Returns the hash code for this BigInteger. |
| int intValue() | Converts this BigInteger to an int. |
| int intValueExact() | Converts this BigInteger to an int, checkingfor lost information. |
| long longValue() | Converts this BigInteger to a long. |
| long longValueExact() | Converts this BigInteger to a long, checkingfor lost information. |
| BigInteger max(BigInteger val) | Returns the maximum of this BigInteger and val. |
| BigInteger min(BigInteger val) | Returns the minimum of this BigInteger and val. |
| BigInteger mod(BigInteger m) | Returns a BigInteger whose value is (this mod m). |
| BigInteger modInverse(BigInteger m) | Returns a BigInteger whose value is (this-1 mod m). |
| BigInteger modPow(BigInteger exponent, BigInteger m) | Returns a BigInteger whose value is (this^exponent mod m). |
| BigInteger multiply(BigInteger val) | Returns a BigInteger whose value is (this * val). |
| BigInteger negate() | Returns a BigInteger whose value is (-this). |
| BigInteger xor(BigInteger val) | Returns a BigInteger whose value is (this ^ val). |
| BigInteger subtract(BigInteger val) | Returns a BigInteger whose value is (this - val). |
| BigInteger not() | Returns a BigInteger whose value is (~this). |
| BigInteger pow(int exponent) | Returns a BigInteger whose value is (this^exponent). |
| String toString() | 返回当前BigInteger对象的十进制字符串表示 |
| String toString(int p) | 返回当前BigInteger对象的p进制字符串表示 |
| BigInteger remainder(BigInteger val) | 返回当前大整数对象与参数指定的大整数对象的余 |
| … | … |
例子
/*
* 计算两个大整数的和，商，差，积，并计算一个大整数的因子个数
*/
package Liu;
import java.math.BigInteger;
import java.util.Scanner;
public class ArrayMethodDemo1 {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
BigInteger b1 = new BigInteger("987654321987654321987654321");
BigInteger b2 = new BigInteger("123456789123456789123456789");
//输出和
System.out.println(b1 + "+" + b2+ "=" + b1.add(b2));
//输出差
System.out.println(b1 + "-" + b2+ "=" + b1.subtract(b2));
//输出乘积
System.out.println(b1 + "*" + b2+ "=" + b1.multiply(b2));
//输出商
System.out.println(b1 + "/" + b2+ "=" + b1.divide(b2));
//求因子个数
int num = 0;
BigInteger m = new BigInteger("77889988");
BigInteger Zero = new BigInteger("0");
BigInteger One = new BigInteger("1");
BigInteger Two = new BigInteger("2");
for(BigInteger i = Two;i.compareTo(m)<0;i=i.add(One)) {
if(m.remainder(i).compareTo(Zero)==0) {
num++;
}
}
System.out.println("大整数77889988共有" + num + "个因子");
}
}
输出：
987654321987654321987654321+123456789123456789123456789=1111111111111111111111111110
987654321987654321987654321-123456789123456789123456789=864197532864197532864197532
987654321987654321987654321*123456789123456789123456789=121932631356500531591068431581771069347203169112635269
987654321987654321987654321/123456789123456789123456789=8
大整数77889988共有46个因子