java常用类

package A01usuallyclass;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Random;
import java.util.Scanner;

public class Usuallyclass {
    public static void main(String[] args) {
//        Scanner scanner = new Scanner(System.in);
//        int i = scanner.nextInt();
//        System.out.println("刚才输入的数字是："+i);

//        Random random = new Random();
//        System.out.println(random.nextInt(10));//[0,10)

//        ArrayList<String> strings = new ArrayList<>();
//        strings.add("linlong");
//        strings.add("dingcaiyan");
//        strings.add("linjincheng");
//        for (int i = 0; i < strings.size(); i++) {
//            System.out.println(strings.get(i));
//        }

//        String str = "linlong";
//        System.out.println("LINLONG".equalsIgnoreCase(str));
//        System.out.println(str.substring(3, str.length()));//左开右闭
//        System.out.println(str.replaceAll("l", "g"));
//        String[] ls = str.split("l");
//        for (int i = 0; i < ls.length; i++) {
//            System.out.println(i + ":" + ls[i]);
//        }

//        int[] arr = {5, 8, 3, 4, 9, 2, 7, 6, 1};
//        System.out.println(Arrays.toString(arr));
//        Arrays.sort(arr);
//        System.out.println(Arrays.toString(arr));

        double num = -6.18;
        System.out.println(Math.abs(num));//绝对值
        System.out.println(Math.ceil(num));//向上取整
        System.out.println(Math.floor(num));//向下取整
        System.out.println(Math.round(num));//四舍五入
    }
}