Java学习记录(补充一(以习题为主:判断,循环语句))

习题1:取一个四位数,求各个位数数字的和package Day2;

import java.util.Scanner;

public class Demo01 {
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        System.out.println("请输入你的卡号");
        int cardNum = in.nextInt();
//        1234
        int i1 = cardNum % 10;
        int i2 = cardNum/10%10;
        int i3 = cardNum/100%10;
        int i4 = cardNum/1000;

        int result = i1+i2+i3+i4;
        System.out.println("会员卡号之和:"+result);
    }
}

结果图:

基本数据类型与包装类之间的转换package Day2;

public class Demo021 {
    public static void main(String[] args) {
//        基本数据类型转换为包装类的方法   valueOf()

        byte b = 21;//基本数据类型
        Byte b2 = Byte.valueOf("21");  //包装数据类型（装箱）
        System.out.println(b2.MAX_VALUE);
        System.out.println(b2.MIN_VALUE);
        System.out.println(b2.SIZE);

        short s = 123;//基本数据类型
        Short s2 = Short.valueOf("123");
        System.out.println(s2.MAX_VALUE);
        System.out.println(s2.MIN_VALUE);
        System.out.println(s2.SIZE);

//        int--->Integer valueOf(装箱)可以使用包装类的方法
        Integer i1 = Integer.valueOf(5);

//        Integer--->int  xxxValue(拆箱)
        int i2 = i1.intValue();

//        字符串--->基本数据类型   parseXXX
        int i3 = Integer.parseInt("123");
        System.out.println(i3);

        boolean b1 = Boolean.parseBoolean("1");
        System.out.println(b1);

        short s3 = Short.parseShort("123");
        System.out.println(s3);

//        基本数据类型--->字符串    String.valueOf()
        String s4 = String.valueOf(1);
        System.out.println(s4);
    }
}

转换总结package Day2;

public class Demo022 {

    public static void main(String[] args) {
//        基本数据类型     --->    包装类 valueOf(三种)
        Integer i1 = Integer.valueOf(23);
        Integer i2 = new Integer(24);
        Integer i3 = 25;

//        包装类    ----->   基本数据类型 xxxValue
        int i4 = i1.intValue();
        int i5 = i2;

//        String  ---- >基本数据类型    

        int i6 = Integer.parseInt("123");
        System.out.println(i6);

//        基本数据类型    ---->   String

        String s1 = String.valueOf(123);

        String s2 = Integer.toString(123);
        System.out.println(s2);

        float f = 12.5F;
//        强制类型转换会损失精度
        int ccy = (int)f;
        System.out.println(ccy);

        System.out.println(6.0%4);

    }
}

结果图;

习题2:(if-else语句)package Day2;

import java.util.Scanner;

public class Demo03 {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.println("请输入你的成绩");
        int score = input.nextInt();
        if (score > 90) {
            System.out.println("A");
        } else if (score >= 80) {
            System.out.println("B");
        } else if (score >= 60) {
            System.out.println("C");
        } else {
            System.out.println("D");
        }
    }
}

结果图:

习题3:(switch语句)package Day2;
import java.util.Scanner;
public class Demo04 {
    public static void main(String[] args) {
        System.out.println("商品列表:");
        System.out.println("1:绿茶,三元");
        System.out.println("2:冰红茶,三元");
        System.out.println("3:脉动,五元");
        System.out.println("4:咖啡,五元");
        System.out.println("5:酸奶,六元");
        Scanner input = new Scanner(System.in);
        System.out.println("请输入你要购买的商品的序号");
        int num = input.nextInt();
        switch(num){
        case 1 :
            System.out.println("您买的绿茶,请支付三元");
            break;
        case 2 :
            System.out.println("您买的冰红茶,请支付三元");
            break;
        case 3 :
            System.out.println("您买的脉动,请支付五元");
            break;
        case 4 :
            System.out.println("您买的咖啡,请支付五元");
            break;
        case 5 :
            System.out.println("您买的酸奶,请支付六元");
            break;
        default:
            System.out.println("您输入的商品序号有误");
        }
    }
}

结果图:

习题4:(do-while语句嵌套if语句)package Day2;

import java.util.Scanner;

public class Demo05 {
    public static void main(String[] args) {
        System.out.println("欢迎进入我行我素管理系統");
        System.out.println("------------------");
        Scanner scanner = new Scanner(System.in);
        do{
            System.out.println("请输入会员号(四位整数)");
            int cardNo = scanner.nextInt();//.nextInt:接收整形数据
            System.out.println("请输入会员生日[月/日<用两位数表示>]");
            String birthDay = scanner.next();//.next:接收字符串数据
            System.out.println("请输入积分");
            int score = scanner.nextInt();
            if(cardNo>999&&cardNo<10000){
                System.out.println("会员卡号为"+cardNo);
                System.out.println("会员生日为"+birthDay);
                System.out.println("会员积分为"+score);
                System.out.println("信息录入成功");
                break;
            }else{

                System.out.println("登入信息失败");
            }
        }while(true);
    }
}

结果图;

习题5:(do-while语句嵌套if-else语句)package Day2;

import java.util.Scanner;

public class Demo06 {
    public static void main(String[] args) {
        System.out.println("请输入会员积分");
        Scanner input = new Scanner(System.in);
        boolean goOn = false;
        do {
            int cardNo = input.nextInt();
            if (cardNo < 2000) {
                System.out.println("该会员可享受九折");
            } else if (cardNo < 4000) {
                System.out.println("该会员可享受八折");
            } else if (cardNo < 8000) {
                System.out.println("该会员可享受七折");
            } else {
                System.out.println("该会员可享受六折");
            }
            System.out.println("是否继续(y/n)?");
            String result = input.next();
            if (result.equals("y")) {
                goOn = true;
                System.out.println("请再次输入积分");
            } else {
                goOn = false;
            }
        } while (goOn);
    }
}

结果图:

习题6:(do-while语句同时嵌套switch和if语句)package Day2;

import java.util.Scanner;

public class Demo07 {

    public static void main(String[] args) {
        System.out.println("请选择想要购买的商品编号");
        System.out.println("1.T恤\t2.网球鞋\t3.网球拍");
        Scanner scanner = new Scanner(System.in);
        boolean goOn = false;
        do {
            System.out.println("请输入想要购买的商品编号");
            int node = scanner.nextInt();
            System.out.println("请输入想要购买的数量");
            int num = scanner.nextInt();
            int sum1 = 245;
            int sum2 = 570;
            int sum3 = 300;

            switch (node) {
            case 1:
                System.out.println("T恤$245.0" + "\t数量" + num + "\t合计$" + sum1 * num);
                break;
            case 2:
                System.out.println("网球鞋$570.0" + "\t数量" + num + "\t合计$" + sum2 * num);
                break;
            case 3:
                System.out.println("网球拍$300.0" + "\t数量" + num + "\t合计$" + sum3 * num);
                break;
            default:
                break;
            }
            System.out.println("是否要继续(y/n)?");
            String result = scanner.next();
            if (result.equals("y")) {
                goOn = true;
            } else {
                goOn = false;
                int all = (sum1 * num + sum2 * num + sum3 * num);
                System.out.println("折扣:0.8");
                System.out.println("实付金额:" + all * 0.8);
                System.out.println("应付金额:" + all);
                System.out.println("找钱:" + all * 0.2);
            }
        } while (goOn);
        System.out.println("欢迎下次光临哦~小肥羊");
    }
}

结果图:

习题7:(do-while语句嵌套while语句(内涵if语句);外含if语句;注意语句中Continue和break的用法)package Day2;
import java.util.Scanner;
public class Demo08 {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String password = "111111";//银行卡密码
        int passwordNum = 0;//密码输入次数
        boolean passWordPass = false;//密码在三次以内通过
        do {
            System.out.println("请输入密码：");
            if(!scanner.next().equals("111111")){
                passwordNum++;
                continue;
            }
            passWordPass = true;
            System.out.println("请输入取款金额：");
            int money = scanner.nextInt();
            while(money > 0){
                if(money<=1000 && money%100==0){
                    System.out.println("您取了" +money+ "元");
                    System.out.println("交易完成，请取卡！");
                    break;                //完成交易，退出
                }else{
                    System.out.print("您输入金额的金额不合法，请重新输入：");
                    money = scanner.nextInt();
                    continue;            //继续让用户输入金额
                }
            }
        } while (passwordNum < 3 && !passWordPass);
        if(!passWordPass){
            System.out.println("密码输入错误三次，请取卡！");
        }
    }
}

结果图: