Java学习_day004：Scanner与分支结构

港控/mmm° 2023-07-20 13:46 9阅读 0赞

### 一、 Scanner ###

**给变量赋值有三种方式：**  
① int a=5；  
②接收用户输入的值；int a=？；（Scanner）  
③系统随机生成值；  
**关于Scanner的语法：**  
①在package下：import java.util.Scanner;  
②在main中：Scanner scan=new Scanner（System.in）;  
③在第二步下面：System.out.println(“name”);  
String name=scan.next();

package day04;
    import java.util.Scanner;//1
    public class ScannerDemo { 
    
    	public static void main(String[] args) { 
    Scanner scan=new Scanner(System.in);//2
    System.out.println("name");
    String name=scan.next();//3
    System.out.println("age");
    int age=scan.nextInt();//3
    System.out.println("prince");
    double prince=scan.nextDouble();//3
    
    System.out.println("我的名字是"+name+",今年"+age+"岁，早餐消费了"+prince+"元。");
    		}
    	}

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpdHRlcl9t_size_16_color_FFFFFF_t_70]

### 二、 分支结构 ###

任何复杂的程序逻辑都可以通过三种结构实现。  
顺序结构：从上往下逐行执行，每句必走；  
分支结构：有条件的执行某语句，并非每句都走；  
循环结构：next day；

#### 1、 **if结构**\* ####

*      if结构：一条路
 *  语法：
 *      if(boolean){
 *      语句块-----基于条件执行的语句
 *      }
 *  执行过程：
 *      判断boolean的值：
 *      若为true，则执行语句块；
 *      若为false，则不执行语句块；
 *      注意不要在小括号和大括号之间加分号，且大括号不能省去；

#### 2、**if…else结构**\* ####

*  if…else结构：两条路，必走其中之一；
 *  1、语法：
 *      if(boolean){
 *      语句块1
 *      }else{
 *      语句块2
 *      }
 *  2、执行过程：
 *      判断boolean的值：
 *      若为true，则执行语句块1；
 *      若为false，则执行语句块2；

#### 3、if…else if结构 ####

*      if...else if结构：多路
 *  1、语法：
 *      if(boolean-1){
 *      语句块1
 *      }else if(boolean-2){
 *      语句块2
 *      }else if(boolean-3){.....
 *      ...}else{
 *      语句块n
 *      }
 *  2、执行过程：判断boolean-1的值：
 *      若为true，则执行语句块1（over）；
 *      若为false，则执行判断boolean-2（同上类推直至到else）。
 *  3、 所有语句块必走其中一个

#### 4、switch…case结构 ####

*      好处：效率高、结构清晰
 *      坏处：只能整数操做，只能判断相等
 *      break：跳出switch

case后面的数不可以重复；  
defualt写哪里都可以；  
只支持byte,short,char,int ，String，  
能用其解决的问题都能用if、、、else if实现  
**练习：**

package day04;
    import java.util.Scanner;//Scanner演示第1步
    public class ScannerDemo { 
    
    	public static void main(String[] args) { 
            Scanner scan=new Scanner(System.in);//Scanner演示第2步
    		System.out.println("请输入年龄");//Scanner演示第3步
    		int age=scan.nextInt();
    		System.out.println(age);
    		System.out.println("请输入价格");
    		double price=scan.nextDouble();
    		System.out.println(age);
    		System.out.println(price);
    		/*5 import java.util.Scanner; * Scanner scan?=new Scanner(System.in); * System.out.println("请输入年龄"); * int age=scan?.nextInt(); * System.out.println("请输入价格"); * double money=scan?.nextDouble(); * System.out.println(age); * System.out.println(money); */
    		/*4 import java.util.Scanner; * Scanner scan=new Scanner(System.in); * System.out.println("请输入年龄"); * int age=scan.nextInt(); * System.out.println("请输入价格"); * double money=scan.nextDouble(); * System.out.println(age); * System.out.println(money); */
    		/*3 import java.util.Scanner; * Scanner scan=new Scanner(System.in); * System.out.println("请输入年龄"); * int age=scan.nextInt(); * System.out.println("请输入金额"); * double money=scan.nextDouble(); * System.out.println("age="age); * System.out.println("money="money); */
    		/*2 import java.util.Scanner; * Scanner scan=new Scanner(System.in); * System.out.println("请输入岁数"); * int age=scan.nextInt(); * System.out.println("请输入金额"); * double money=scan.nextDouble(); * System.out.println(age); * System.out.println(money); */
    		/*1 import java.util.Scanner; * Scanner scan=new Scanner(System.in); * System.out.println("请输入年龄"); * int age=scan.nextInt(); * System.out.println("请输入价格"); * double money=scan.nextDouble(); * System.out.println(age); * System.out.println(money); */

double money=600;
    		if(money>500){ 
    			money*=0.8;
    		}
    		System.out.println(money);
    		int num=5;
    		if(num%2==0){ 
    		    System.out.println(num+"是偶数");
    		}
    		System.out.println("over");
    		/*5 int num=6; * double money=600; * if(num%2==0){ *System.out.println(num+"是偶数"); *} *if(money>500){ *money*=0.8; *{ *System.out.println(money); *System.out.println("over"); */
    		/*4 int num=7; * double price=666; * if(num%2==0){ * System.out.println(num+"是偶数"); * } * if(price>500){ * price*=0.8; * } * System.out.println(price); * System.out.println("over"); */
    		/*3 int num=8; * double money=789; * if(num%2==0){ * System.out.println(num+"是偶数"); * } * if(money>500){ * money*=0.8; * } * System.out.println(money); * System.out.println("over"); */
    		/*2 int num=9; * double price=532.2; * if(num%2==0){ * System.out.println(num+"是偶数"); * } * if(price>500){ * price*=0.7; * } * System.out.println(price); * System.out.println("over"); */
    		/*1 int num=55; * double money=499.8; * if(num%2!=0){ * System.out.println(num+"是奇数"); * } * if(money>500){ * money*=0.8; * } * System.out.println(money); * System.out.println("over"); */

double money=600;
    		if(money>500){ 
    			money*=0.8;
    		}else{ 
    			money*=0.9;
    		}
    		System.out.println("消费金额"+money);
    		int num=6;
    		if(num%2==0){ 
    			System.out.println(num+"是偶数");
    		}else{ 
    			System.out.println(num+"是奇数");
    		}
    		System.out.println("over");
    		/*5 int num=7; * double price=782.2; * if(num%2==0){ * System.out.println(num+"是偶数"); * }else{ * System.out.println(num+"是奇数"); * } * if(price>500){ * price*=0.8; * }else{ * price*=0.9 * } * System.out.println("消费金额"+price); * System.out.println("over"); */
    		/*4 int num=55; * double money=777; * if(money>500){ * money*=0.8; * }else{ * money*=0.9; * } * System.out.println("消费金额"+money); * if(num%2==0){ * System.out.println(num+"是偶数"); * }else{ * System.out.println(num+"是奇数"); * } * System.out.println("over"); */
    		/*3 int a=2; * double b=621; * if(a%2==0){ * System.out.println(a+"是偶数"); * }else{ * System.out.println(a+"是奇数"); * } * if(b>500){ * b*=0.75; * }else{ * b*0.9; * } * System.out.println("消费金额"+b); * System.out.println("over"); */
    		/*2 double $=4546; * int num=6; * if($>600){ * $*=0.7; * }else{ * $*=0.9; * } * System.out.println("消费金额"+$); * if(num%2!=0){ * System.out.println(num+"是奇数"); * }else{ * System.out.println(num+"是偶数"); * } * System.out.println("over"); */
    		/*1 double money=500.2; * int num=6; * if(money>480){ * money*=0.8; * }else{ * money*=0.9; * } * System.out.println("消费金额"+money); * if(num%2==0){ * System.out.println(num+"是偶数"); * }else{ * System.out.println(num+"是奇数"); * } * System.out.println("over"); */

if(scor<0||scor>100){ 
    			System.out.println("成绩不合法");
    		}else if(scor>=90){ 
    			System.out.println("A-优秀");
    		}else if(scor>=80){ 
    			System.out.println("B-良好");
    		}else if(scor>=60){ 
    			System.out.println("C-中等");
    		}else{ 
    			System.out.println("D-不及格");
    		}
    		//120,98,85,75,64
    		/*5 double scor=120; * if(scor>100||scor<0){ * System.out.println("成绩不合法"); * }else if(scor>=90){ * System.out.println("A-优秀"); * }else if(scor>=80){ * System.out.println("B-良好"); * }else if(scor>=60){ * System.out.println("C-中等"); * }else{ * System.out.println("D-不合格"); * } */
    		/*4 double scor=96; * if(scor>100||scor<0){ * System.out.println("成绩不合法"); * }else if(scor>=90){ * System.out.println("A-优秀"); * }else if(scor>=80){ * System.out.println("B-良好"); * }else if(scor>=60){ * System.out.println("C-中等"); * }else{ * System.out.println("D-不合格"); */
    		/*3 double scor=86; * if(scor>100||scor<0){ * System.out.println("成绩不合法"); * }else if(scor>=90){ * System.out.println("A-优秀"); * }else if(scor>=80){ * System.out.println("B-良好"); * }else if(scor>=60){ * System.out.println("C-中等"); * }else{ * System.out.println("D-不合格"); * } */
    		/*2 double scor=67; * if(scor>100||scor<0){ * System.out.println("成绩不合法"); * }else if(scor>=90){ * System.out.println("A-优秀"); * }else if(scor>=80){ * System.out.println("B-良好"); * }else if(scor>=60){ * System.out.println("C-中等"); * }else{ * System.out.println("D-不合格"); * } */
    		/*1 double scor=58; * if(scor>100||scor<0){ * System.out.println("成绩不合法"); * }else if(scor>=90){ * System.out.println("A-优秀"); * }else if(scor>=80){ * System.out.println("B-良好"); * }else if(scor>=60){ * System.out.println("C-中等"); * }else{ * System.out.println("D-不合格"); * } */

Scanner scan=new Scanner(System.in);
    		System.out.println("请选择功能：1.显示全部记录 2.查询登录记录 3.修改账户信息 0.退出");
    		int command=scan.nextInt();
    		
    		switch(command){ 
    		case 1:
    			System.out.println("此处做显示全部记录操纵");
    			break;
    		case 2:
    			System.out.println("登录");
    			break;
    		case 3:
    			System.out.println("查询");
    			break;
    		case 0:
    			System.out.println("欢迎下次再来");
    			break;
    		default:
    			System.out.println("输入错误");
    		}
    		if(command==1){ 
    			System.out.println("此处做显示全部记录操纵");
    		}else if(command==2){ 
    			System.out.println("登录");
    		}else if(command==3){ 
    			System.out.println("查询");
    		}else if(command==0){ 
    			System.out.println("欢迎下次再来");
    		}else{ 
    			System.out.println("输入错误");
    		}
    		/*5 System.out.println("请输入") * int command=?; * switch (command){ * case 1: * System.out.println("查询"); * break; * case 2: * System.out.println("登录"); * break; * case 3: * System.out.println("注册"); * break; * case 0: * System.out.println("退出"); * break; * default: * System.out.println("错误"); * } * if(command==1){ * System.out.println("查询"); * }else if(command==2){ * System.out.println("登录"); * }else if(command==3){ * System.out.println("注册"); * }else if(command==0){ * System.out.println("退出"); * }else{ * System.out.println("错误"); * } */
    		/*4 switch (command){ * case 1: * System.out.println("记录"); * break; * case 2: * System.out.println("登录"); * break; * case 3: * System.out.println("注册"); * break; * case 0: * System.out.println("退出"); * break; * default; * System.out.println("错误"); * } * if(command==1){ * System.out.println("显示"); * }else if(command==2){ * System.out.println("登录"); * }else if(command==3){ * System.out.println("注册"); * }else if(command==0){ * System.out.println("退出"); * }else{ * System.out.println("错误"); * } */
    		/*3 switch (command){ * case 1: * System.out.println("上"); * break; * case 2: * System.out.println("下"); * break; * case 3: * System.out.println("跳"); * break; * case 0: * System.out.println("退出"); * break; * default; * System.out.println("错误"); * } * if(command==1){ * System.out.println("上"); * }else if(command==2){ * System.out.println("下"); * }else if(command==3){ * System.out.println("跳"); * }else if(command==0){ * System.out.println("退出"); * }else{ * System.out.println("错误"); * } */
    		 /*2 switch (command){ * case 1: * System.out.println("←"); * break; * case 2: * System.out.println("↑"); * break; * case 3: * System.out.println("↓"); * break; * case 0: * System.out.println(" "); * break; * default; * System.out.println("错误"); * } * if(command==1){ * System.out.println("←"); * }else if(command==2){ * System.out.println("↑"); * }else if(command==3){ * System.out.println("↓"); * }else if(command==0){ * System.out.println(" "); * }else{ * System.out.println("错误"); * } */
    		/*1 switch (command){ * case 1: * System.out.println("%"); * break; * case 2: * System.out.println("￥"); * break; * case 3: * System.out.println("#"); * break; * case 0: * System.out.println("@"); * break; * default; * System.out.println("！"); * } * if(command==1){ * System.out.println("%"); * }else if(command==2){ * System.out.println("￥"); * }else if(command==3){ * System.out.println("#"); * }else if(command==0){ * System.out.println("@"); * }else{ * System.out.println("！"); * } */

//两个数的排序
    		int a=8,b=55;
    		if(a>b){ 
    			int t=a;
    			a=b;
    			b=t;
    		}
    		System.out.println(a+","+b);
    		
    		//交换两个数
    		int c=8,d=5;
    		int t=c;
    		c=d;
    		d=t;
    		/* * 交换两个数：追尾并绕圈 * int t=a;a=b;b=t; */
    		/*5 int a=4,b=5,c=6,d=7; * if(a>b){ * int t=a; * a=b; * b=t; * } * System.out.println(a+","+b); * int t=c; * c=d; * d=t; */
    		/*4 int a=4,b=5,c=6,d=7; * if(a>b){ * int t=a; * a=b; * b=t; * } * System.out.println(a+","+b); * int t=c; * c=d; * d=t; */
    		/*3 int a=7,b=8; * if(a>b){ * int t=a; * a=b; * b=t; * } * System.out.println(a+","+b); * int t=a; * a=b; * b=a; */
    		/*2 int a=2,b=1; * if(a>b){ * int t=a; * a=b; * b=t; * } * System.out.println(a+","+b); * int t=a; * a=b; * b=t; */
    		/*1 int a=6,b=9; * if(a>b){ * int t=a; * a=b; * b=t; * } * System.out.println(a+","+b); * int t=b; * b=a; * a=t; */

int year=2020,month=2,day=0;
    		switch(month){ 
    		case 1:
    		case 3:
    		case 5:
    		case 7:
    		case 8:
    		case 10:
    		case 12:
    			day=31;
    			break;
    		case 4:
    		case 6:
    		case 9:
    		case 11:
    			day=30;
    			break;
    		case 2:
    			if(year%400==0||(year%4==0&&year%100!=0)){ 
    				day=29;
    			}else{ 
    				day=28;
    			}
    			
    		}
    		System.out.println(year+"年"+month+"月是"+day+"天");		
    		/*5 int year=1997,month=4,day=0; * switch(month){ * case 1: * case 3: * case 5: * case 7: * case 8: * case 10: * case 12: * day=31; * break; * case 4: * case 6: * case 9: * case 11: * day=30; * break; * case 2: * if(year%400||(year%4==0&&year%100!=0)){ * day=29; * }else{ * day=28; * } * } * System.out.println(year+"年"+month+"月是"+day+"天"); */
    		/*4 int day=0,month=4,year=1998; * switch(month){ * case 1: * case 3: * case 5: * case 7: * case 8: * case 10: * case 12: * day=31; * break; * case 4: * case 6: * case 9: * case 11: * day=30; * break; * case 2: * if(year%400==0||year%4==0&&year%100!=0){ * day=29; * }else{ * day=28; * } * } * System.out.println(year+"年"+month+"月是"+day+"天"); */
    		/*3 int year=2015,month=5,day=1; * switch(month){ * case 1: * case 3: * case 5: * case 7: * case 8: * case 10: * case 12: * day=31; * break; * case 4: * case 6: * case 9: * case 11: * day=30; * break; * case 2: * if(year%400==0||year%4==0&&year%100!=0){ * day=29; * }else{ * day=28; * } * } * System.out.println?(year+"年"+month+"月是"+day+"天"); */
    		/*2 int year=2008,month=12,day=0; * switch(month){ * case 1: * case 3: * case 5: * case 7: * case 8: * case 10: * case 12: * day=31; * break; * case 4: * case 6: * case 9: * case 11: * day=30; * break; * case 2: * if(year%4==0&&year%100!=0||year%400==0){ * day=29; * }else{ * day=28; * } * } * System.out.println(year+"年"+month+"月是"+day+"天"); */
    		/*1 int year=2028,month=5,day=8; * switch(month){ * case 1: * case 3: * case 5: * case 7: * case 8: * case 10: * case 12: * day=31; * break; * case 4: * case 6: * case 9: * case 11: * day=30; * case 2" * if(year%400==0||year%4==0&&year%100!=0){ * day=29; * }else{ * day=28; * } * } * System.out.println(year+"年"+month+"月是"+day+"天"); */

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpdHRlcl9t_size_16_color_FFFFFF_t_70]: /images/20230528/e9d4a863d8d34e2da148ad2d219fb601.png