Java基础常用类：ArraysMath类

Posted 2020-12-09 Firefly

一、Arrays类

import java.util.Arrays;

/*
java.util.Arrays是一个数组有关的工具类，里面提供大量静态方法

public static String toString(数组)：数组转为字符串
public static void sort(数组):将数组元素默认按照升序排列
    如果是数值，sort默认按照升序从小到大
    如果是字符串，sort默认按照字母升序
 */
public class Demo08Arrays {
    public static void main(String[] args) {
        int[] intArray = {1, 20, 30};

        String intStr = Arrays.toString(intArray);
        System.out.println(intStr);//[1, 20, 30]

        int[] array1 = {2, 5, 1, 9, 4};
        Arrays.sort(array1);
        System.out.println(Arrays.toString(array1));//[1,2,4,5,9]

        String[] array2 = {"sss", "ccc", "aaa"};
        Arrays.sort(array2);
        System.out.println(Arrays.toString(array2));//[aaa, ccc, sss]

　　}
}

 

二、数学工具类Math

/*
java.util.Math类是数学相关的工具类，其提供了大量的静态方法

public static double abs(double num):获取绝对值,参数也可以是int/float/long等
public static double ceil(double num):向上取整
public static double floor(double num):向下取整
public static long round(double num):四舍五入

Math.PI代表近似的圆周率
 */
public class Demo09Math {

    public static void main(String[] args) {
        //获取绝对值
        System.out.println(Math.abs(-3));//3
        
        //向上取整
        System.out.println(Math.ceil(2.99));//3.0
        System.out.println(Math.ceil(2.1));//3.0

        //向下取整
        System.out.println(Math.floor(123.95));//123.0
        System.out.println(Math.floor(123.12));//123.0

        //四舍五入且取整
        System.out.println(Math.round(1.2));//1
        System.out.println(Math.round(1.5));//2

        System.out.println(Math.PI);//3.141592653589793
    }
}