Java学习之简单案例

2021-06-23

一些基础案例

1.排序

1.1代码演示

package Java_easy_Casestudy;

public class Sort_Demo {
    public static void main(String[] args) {
        int[] numbers = {44, 99, 22, 11, 55, 33, 88, 66, 77};
        System.out.println("排序前" + arrayToString(numbers));
        for (int x = 0; x < numbers.length - 1; x++){
            for (int y = 0; y < numbers.length - 1 - x; y++){
                if (numbers[y] > numbers[y+1]) {
                    int temp = numbers[y];
                    numbers[y] = numbers[y + 1];
                    numbers[y + 1] = temp;
                }
            }
        }
        System.out.println("排序后"+ arrayToString(numbers));
    }
    public static String arrayToString(int[] arr){
        StringBuilder sb = new StringBuilder();
        sb.append('[');
        for (int i = 0; i < arr.length; i++){
            if (i == arr.length - 1){
                sb.append(arr[i]);
            }else {
                sb.append(arr[i]);
                sb.append(',');
            }
        }
        sb.append(']');
        String s = sb.toString();
        return s;
    }
}

2.字符串排序

2.1代码演示

package Java_Array;

import java.util.Arrays;

public class Java_字符串数据排序 {
    public static void main(String[] args) {
        String str = "55 22 44 11 99 88 66 77 33";
        //分割字符串中的数据
        String[] str_array = str.split(" ");
        int[] arr = new int[str_array.length];
        for (int i = 0; i < arr.length; i++){
            //将字符串数组转化为int类型的数组
            arr[i] = Integer.parseInt(str_array[i]);
        }
        Arrays.sort(arr);
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < arr.length; i++){
            if (i == arr.length - 1){
                sb.append(arr[i]);
            }else {
                sb.append(arr[i]).append(" ");
            }
        }
        String result = sb.toString();
        System.out.println(result);
    }
}
//输出结果
/*
	11 22 33 44 55 66 77 88 99
*/

3.日期格式化和解析

3.1代码演示

package Java_简单案例;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class Java_日期工具类 {
    private Java_日期工具类 (){

    }

    public static String DateToString (Date date, String format){
        SimpleDateFormat sdf = new SimpleDateFormat(format);
        String s = sdf.format(date);
        return s;
    }

    public static Date stingToDate(String s, String format) throws ParseException {
        SimpleDateFormat sdf = new SimpleDateFormat(format);
        Date s_1 = sdf.parse(s);
        return s_1;
    }
}

package Java_简单案例;

import java.text.ParseException;
import java.util.Date;

public class Java_日期测试类 {
    public static void main(String[] args) throws ParseException {
        Date d_1 = new Date();
        String d_2 = Java_日期工具类.DateToString(d_1, "yyyy年MM月dd日 HH:mm:ss");
        System.out.println(d_2);

        String d_3 = "2022-07-03 11:22:33";
        Date d_4 = Java_日期工具类.stingToDate(d_3, "yyyy-MM-dd HH:mm:ss");
        System.out.println(d_4);
    }
}
//输出结果
/*
	2021年07月03日 14:00:40
	Sun Jul 03 11:22:33 CST 2022
*/

4.计算任意年份的2月有多少天

4.1代码演示

package Java_简单案例;

import java.util.Calendar;
import java.util.Scanner;

public class Java_计算任意年份的2月天数 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("请输入年份：");
        int year = sc.nextInt();
        Calendar c_1 = Calendar.getInstance();
        c_1.set(year, 2, 1);
        c_1.add(Calendar.DATE, -1);
        int date = c_1.get(Calendar.DATE);
        System.out.println(year + "年的2月份有" + date + "天");
    }
}
//输出结果
/*
	请输入年份：2021
	2021年的2月份有28天
*/