```java
##基本数据类型
###设计一个方法，将一个小于2147483647的double类型变量以截断取整方式转化为int类型
import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double d = scanner.nextDouble();
        System.out.println(Main.typeConversion(d));
    }
    public static int typeConversion(double d){
        return (int)d;
    }
}
##运算符
###输入两个正整数a和b，输出这两个正整数的和，差，积，商，模（若a>b则输出a-b，a/b，a%b的值反之输出b-a，b/a，b%a的值，不考虑小数，请使用int类型）

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int a = scanner.nextInt();
        int b = scanner.nextInt();
        scanner.close();
        if(a<=b){

    int temp=a;
    a=b;
    b=temp;
}
    System.out.printf("%d %d %d %d %d",a+b,a-b,a*b,a/b,a%b);
}

}
###定义一个int类型变量i,i为由浮点数变量d四舍五入后的整数类型，请将转换后的i进行输出
import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double d= scanner.nextDouble();
        int i=(int)d;
         if((d-i)>0.5){
             i++;
         }
        System.out.println(i);
    }
}
###在不使用第三个变量的情况下交换两个int类型变量的值
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int a = scanner.nextInt();
        int b = scanner.nextInt();
        int temp = a;
        a = b;
        b = temp;
        System.out.println(a+" "+b);
    }
}
##分支
###牛牛商场促销活动：
满100全额打9折；
满500全额打8折；
满2000全额打7折；
满5000全额打6折；
且商场有抹零活动，不足一元的部分不需要付款（类型强制转换）
牛大姨算不清楚自己应该付多少钱，请你帮忙算一下
import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner console = new Scanner(System.in);
        int price = console.nextInt();
        int cost = 0;
            if(price>=5000){
            cost=(int)(price*0.6);
        }else if(price>=2000){
            cost = (int) (price * 0.7);
        }else if(price>=500){
            cost = (int) (price * 0.8);
        }else if(price>=100){
            cost=(int)(price*0.9);
        }else{
           cost=(int)(price);
        }
        System.out.println(cost);
    }
}
###判断体重指数
import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double height = scanner.nextDouble();
        double weight = scanner.nextDouble();
        double whh=weight/(height*height);
         if(whh>24.9){
            System.out.println("偏胖");
        }else if(whh>=20.9&&whh<=24.9){
            System.out.println("适中");
        }else if(whh>=18.5&&whh<20.9){
            System.out.println("苗条");
        }else{
            System.out.println("偏瘦");
        }
    }
    }
###判断学生成绩等级
import java.util.Scanner;
//switch case 思路
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String grade =scanner.next();
        switch (grade){
         case "A":
         System.out.println("优秀");
         break;
         case "B":
             System.out.println("良好");
             break;
         case "C":
             System.out.println("及格");
             break;
         case "D":
             System.out.println("不及格");
             break;
         default:
             System.out.println("未知等级");
 }
    }
}
###邮箱验证
import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String str = scanner.next();
        String emailMatcher="[a-zA-Z0-9]+@[a-zA-Z0-9]+\\.[a-zA-Z0-9]+";
        if(str.matches(emailMatcher)){
            System.out.println("邮箱格式合法");
        }else{
            System.out.println("邮箱格式不合法");
        }
    }
}