Java 数学操作类

public static int round(float a)

public static double abs(double a)

public static int max(int a , int b)

protected int next (int bits)

import java.util.Random;

public class TestDemo {
	public static void main(String [] args) throws CloneNotSupportedException {
		Random ran = new Random();
		int data[] = new int [7] ; //开辟一个数组
		int foot = 0 ;
		while (foot < 7) {
			int t = ran.nextInt(37); // 随机生成返回一个不大于37的数
			if (!isRepeat(data,t)) { // 查重
				data[foot ++] = t ;
			}
		}
		java.util.Arrays.parallelSort(data);
		for (int x = 0 ; x < data.length ; x ++) {
			System.out.print(data[x] + "\t");
		}
	}
	public static boolean isRepeat(int temp[] , int num) { // 查重
		if (num == 0 ) {
			return true ;
		}
		for (int x = 0 ; x < temp.length ; x ++) {
			if (temp[x] == num) {
				return true ;
			}
		}
		return false;
	}
}

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

public class TestDemo {
	public static void main(String [] args) throws CloneNotSupportedException {
		BigInteger big_A = new BigInteger("12345678912345678912356789");
		BigInteger big_B = new BigInteger("218372948729847298347289") ;
		System.out.println("加法操作 >>> " + (big_A.add(big_B)));
		System.out.println("减法操作 >>> " + (big_A.subtract(big_B)));
		System.out.println("乘法操作 >>> " + (big_A.multiply(big_B)));
		System.out.println("除法操作 >>> " + (big_A.divide(big_B)));
	}
}

加法操作 >>> 12564051861075526210704078
减法操作 >>> 12127305963615831614009500
乘法操作 >>> 2695962308160819899591376721692771747399598895021
除法操作 >>> 56

public BigDecimal(String val) ;
public BigDecimal(double val) ; 

public BigDecimal divide(BigDecimal divisor , int scale , int round);

import java.math.BigDecimal;

class MyMath {
	/**
	 * 实现准确的位数的四舍五入操作
	 * @param num 进行四舍五入操作的数字
	 * @param scale 要保留的小数位数
	 * @return 处理后的数据
	 */
	public static double round(double num , int scale) {
		BigDecimal bigA = new BigDecimal(num) ;
		BigDecimal bigB = new BigDecimal(1) ;
		// ROUND_HALF_UP:向“最接近的”数字舍入
		// doubleValue() : 转 double 型数据
		return bigA.divide(bigB, scale , BigDecimal.ROUND_HALF_UP).doubleValue() ;
	}
}

public class TestDemo {
	public static void main(String [] args) {
		System.out.println(MyMath.round(19.224532 , 2));
		System.out.println(MyMath.round(3.1465926 , 2));
	}
}