day

Scanner
从键盘导入 ：
1.包
import java.util.Scanner;
2.实例化
Scanner s = new Scanner(System.in);
3.调用
int num = s.nextInt()
练习：

Scanner s = new Scanner(System.in);

System.out.println("age(int):");
int    num = s.nextInt();
System.out.println(num);

System.out.println("name(string):");
String name = s.next();
System.out.println(name);

System.out.println("report(double):");
double report = s.nextDouble();
System.out.println(report);

System.out.println("yes?(boolean):");
boolean anser = s.nextBoolean();
System.out.println(anser);

System.out.println("char(1):");
String chars = s.next();
char charss = chars.charAt(1);//1 索引
System.out.println(charss);

if else结构：

        System.out.print(report+ ":" );
        if (report <60){
           System.out.println("不及格");
        }
        else if( report>= 60 && report<75){
            System.out.println("及格");
        }
        else if( report>=75 && report<85){
            System.out.println("良");
        }
        else if( report>=85 && report<=100){
            System.out.println("优");
        }
        else{
            System.out.println("成绩有误");
        }

if-else 的类似结构 switch-case 结构（S-C结构不能表示范围）：

        Scanner scan = new Scanner(System.in);

        String season = scan.next();

        switch(season)
        {
            case "Spring" :
                System.out.println("春");
                break;
            case "Summer" :
                System.out.println("夏");
                break;
            case "autumn" :
                System.out.println("秋");
                break;
            default:
                System.out.println("冬");

        }

for循环

    int sum = 0;
    int count = 0;
        for(int i =100;i > 1;i--)
        {
            if(i%2 ==0 ){
                System.out.print(i+" ");
                sum += i;
                count ++;
            }
        }
        System.out.println();
        System.out.println("总和:"+sum);
        System.out.println("个数:"+count);

之前学习的总和测试：家庭账单

在这里插入代码片package welcome_java;
import  java.util.Scanner;

public class FamilyAccount {
    public static void main(String[] args){
        Scanner scan = new Scanner(System.in);
         boolean isFlag = true;
         double countMoney = 0.0;
         double money = 0.0;
         String details = "收/支      金额      账户金额      备注n";
         String proform = "";
         while(isFlag) {

             System.out.println("-------家庭账单-------");
             System.out.println("1.明细");
             System.out.println("2.收入");
             System.out.println("3.支出");
             System.out.println("4.退出");
             System.out.println("-------家庭账单-------");
             int flag = scan.nextInt();
             switch (flag) {
                 case 1:

                     System.out.println("--------收支明细--------");
                     System.out.println(details);
                     System.out.println("--------收支明细--------");

                     break;
                 case 2:

                     System.out.println("收入金额:");
                     money = scan.nextDouble();
                     countMoney += money;
                     System.out.println("备注");
                     proform = scan.next();
                     details += "收入tt" + money + "tt" + countMoney + "tt" + proform + "n";
                     System.out.println("----记录成功----");
                     break;
                 case 3:
                     System.out.println("支出金额:");
                     money = scan.nextDouble();
                     countMoney -= money;
                     System.out.println("备注");
                     proform = scan.next();
                     details += "支出tt" + money + "tt" + countMoney + "tt" + proform + "n";
                     System.out.println("----记录成功----");
                     break;
                 case 4:
                     System.out.println("确定退出？(Y/N):");
                     String outFlag = scan.next();
                     if (outFlag.equals("Y") || outFlag.equals("y")) {
// 退不出去 因为比较的是地址        if(outFlag == "Y"){
                         isFlag = false;
                         break;
                     }
                 default:
                     System.out.println("输入有误重新输入");
             }
         }
    }
}

java数组：
默认值

• int :0
• double:0.0
• boolean:faluse
• char:0(数字零而非’0’)
• String:null(并不是”null“)

package welcome_java;

import java.sql.SQLOutput;

public class ArrayTest_java {
    public static void main(String[] args){
        int[] array_1;//声明
        array_1 = new int[]{1,2,3,4};//静态初始化

        int[] array_11 = new int[10];//动态初始化
        String[] array_2 = new String[10];//初始化一个空数组


        array_2[0] = "ys";
        array_2[1] = "yss";
        array_2[2] = "ysss";
        for(int i=0;array_2[i]!=null;i++){
            System.out.println(array_2[i]);
        }

        for(int i=0;i<4;i++){
            System.out.println(array_1[i]);
        }
        //获取数组长度
        System.out.println(array_2.length);

        String arr_1[][] = new String[4][3];
//        arr_1[1] = new String[3];

        //二位数字遍历
        for(int i=0;i 
null	null	null	

null	null	null	

null	null	null	

null	null	null