java基础学习例子

1.递增

public class HelloWorld {
    public static void main(String [] args){
        int sum=0;
        for(int i=0;i<=100;i++){
            sum=sum+i; 
        }
        System.out.print(sum);
    }
}

2. 9,99,999,9999,99999累加

public class HelloWorld {
    public static void main(String [] args){
        //9,99,999,9999。。的累加
        long sum=0;
        long num=0;
        for(int i=1;i<=5;i++){
            num=num*10+9;
            sum+=num; 
            System.out.println("第"+i+"轮 ：num:"+num+"    sum"+sum);
        }
        System.out.println("最终"+sum);
    }
}

3.

import java.util.Scanner;
public class HelloWorld {
    public static void main(String [] args){
        Scanner scan=new Scanner(System.in);
        System.out.println("请输入年龄");
        int age=scan.nextInt();
        boolean b=age>=18&&age<=50;
        System.out.println(b);
        
    }
}

闰年

import java.util.Scanner;
public class HelloWorld {
    public static void main(String [] args){
        Scanner scan=new Scanner(System.in);
        System.out.println("请输入年份");
        int year=scan.nextInt();
        boolean rs=year%4==0&&year%100!=0||year%400==0;
        String str=rs?year+"是闰年":year+"不是闰年";
        System.out.println(str);
    }
}

收银台

import java.util.Scanner;
public class HelloWorld {
    public static void main(String [] args){
        Scanner scan=new Scanner(System.in);
        System.out.println("请输入单价");
        double unitprice=scan.nextDouble();
        System.out.println("请输入数量");
        double num=scan.nextDouble();
        System.out.println("请输入金额");
        double money=scan.nextDouble(); 
        double totalprice=unitprice*num;
        double change=money-totalprice;
        System.out.println("应收"+totalprice+"找零"+change);
        
    }
}