Java学习路线-18：数字操作类Math、Random、BigInteger、BigDecimal

Math.abs(-10) // 10
Math.max(10, 1) // 10
Math.pow(10, 2) //100.0
Math.sqrt(9) //3.0
Math.round(10.4) // 10
Math.round(10.5) // 11

class MathUtil {
    private MathUtil() {
    }
    // 自定义保留位数
    public static double round(double num, int scale) {
        return Math.round(num * Math.pow(10, scale)) / Math.pow(10, scale);
    }
}
class Demo {
    public static void main(String[] args) {
        System.out.println(MathUtil.round(10.98766, 2)); // 10.99
    }
}

class Demo {
    public static void main(String[] args) {
        Random random = new Random();
        // 产生随机数范围[0, 10)
        System.out.println(random.nextInt(10));
    }
}

/**
 * 随机示例
 * 36 选 7
 */
class Demo {
    public static int[] getCodeList(){
        int[] data = new int[7];
        int foot = 0;
        Random random = new Random();
        while (foot<7){
            int code = random.nextInt(37);
            if(isUse(code, data)){
                data[foot++] = code;
            }
        }
        return data;
    }
    // 检查号码是否可以使用，不能为0，不能重复
    public static boolean isUse(int code, int[] temp){
        if(code == 0){
            return false;
        }
        for(int x : temp){
            if(code == x){
                return false;
            }
        }
        return true;
    }
    public static void main(String[] args) {
        int[] data = getCodeList();
        for(int x : data){
            System.out.print(x + ", ");
        }
        // 15, 19, 9, 11, 33, 2, 21, 
    }
}

Object
    -Number
        -Integer
        -Byte
        -Long
        -Short
        -Float
        -Double
        -BigInteger
        -BigDecimal
    -Boolean
    -Character

import java.math.BigInteger;
class Demo{
    public static void main(String[] args) {
        BigInteger big1 = new BigInteger("98960973126687599871");
        BigInteger big2 = new BigInteger("98960973126687599872");
        System.out.println(big2.subtract(big1));
        // 1
    }
}

import java.math.BigInteger;
class Demo{
    public static void main(String[] args) {
        BigInteger big1 = new BigInteger("1001");
        BigInteger big2 = new BigInteger("10");
        BigInteger[] ret = big1.divideAndRemainder(big2);
        System.out.println(ret[0] + ", " +  ret[1]);
        // 100, 1
    }
}

import java.math.BigDecimal;
import java.math.RoundingMode;
class MathUtil {
    private MathUtil() {
    }
    // 自定义保留位数
    public static double round(double num, int scale) {
        return new BigDecimal(num).divide(
            new BigDecimal(1.0), scale, RoundingMode.HALF_UP).doubleValue();
    }
}
class Demo {
    public static void main(String[] args) {
        System.out.println(MathUtil.round(10.98766, 2)); // 10.99
    }
}