java 输入与结构

输入

1. 用next方式接收

   package com.kuang.scanner;import java.sql.SQLOutput;
   import java.util.Scanner;public class Demo01 {public static void main(String[] args) {//创建一个扫描器，用于接收键盘数据Scanner scanner = new Scanner(System.in);System.out.println("使用next方式接收：");//判断用户有没有输入字符串if (scanner.hasNext()){//使用next方式接收String str = scanner.next();System.out.println("输出的内容为："+str);}//凡是属于IO流的类如果不关闭会一直占用资源，要用完就关scanner.close();}
   }

2. 用nextline方式接收

   package com.kuang.scanner;import java.util.Scanner;public class Demo02 {public static void main(String[] args) {Scanner scanner = new Scanner(System.in);System.out.println("使用nextLine方式接收");if(scanner.hasNextLine()){String str=scanner.nextLine();System.out.println("输出内容为："+str);}scanner.close();}
   }

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if语句

1. 单选择结构

   package com.kuang.struct;import java.util.Scanner;public class IfDemo01 {public static void main(String[] args) {//单选择结构Scanner scanner = new Scanner(System.in);System.out.println("请输入：");String str=scanner.nextLine();if(str.equals("Hello")){System.out.println(str);}System.out.println("End");scanner.close();}
   }

2. 双选择

   package com.kuang.struct;import java.util.Scanner;public class IfDemo02 {public static void main(String[] args) {//双选择结构Scanner scanner = new Scanner(System.in);System.out.println("输入成绩：");double score= scanner.nextDouble();if(score>=60){System.out.println("及格");}else {System.out.println("不及格");}scanner.close();}
   }

3. 多选择

   package com.kuang.struct;import java.util.Scanner;public class IfDemo03 {public static void main(String[] args) {//多选择结构Scanner scanner = new Scanner(System.in);int score = scanner.nextInt();if(score==100){System.out.println("A+");}else if(score<100&&score>=80){System.out.println('A');} else if (score<80&&score>=60) {System.out.println('B');} else if (score<60&&score>=0){System.out.println("不及格");}else {System.out.println("成绩不合法");}scanner.close();}
   }

switch

package com.kuang.struct;import java.util.Scanner;public class SwitchDemo04 {public static void main(String[] args) {Scanner scanner = new Scanner(System.in);System.out.println("请输入等级：");String grade=scanner.next();switch(grade){case "A":System.out.println("best");break;case "B":System.out.println("great");break;case "C":System.out.println("good");break;case "D":System.out.println("just so so");break;case "E":System.out.println("bad");break;default:System.out.println("invalid");}}
}

while

package com.kuang.struct;public class whileDemo05 {public static void main(String[] args) {int a=1;int sum=0;while(a<=100){sum+=a;a++;}System.out.println(sum);}
}

dowhile

package com.kuang.struct;public class DoWhileDemo06 {public static void main(String[] args) {int a=0;//dowhile先执行再判断do{System.out.println(a);a++;}while (a<0);System.out.println("---------");//while先判断再执行while(a<0){System.out.println(a);a++;}}
}

for

1. for

   package com.kuang.struct;public class ForDemo07 {public static void main(String[] args) {//初始化；条件判断；迭代for (int i=0;i<100;i++){System.out.println(i);}System.out.println("--------------");//分别输出0~100之间奇数和与偶数和int oddsum=0;int evensum=0;for(int i=0;i<=100;i++){if(i%2==0){evensum+=i;}else {oddsum+=i;}}System.out.println("偶数和为："+evensum);System.out.println("奇数和为："+oddsum);System.out.println("--------------");//输出1~1000之间能被5整除的数，每行输出3个int num=0;for(int i=1;i<=1000;i++){if(i%5==0){num++;System.out.print(i+"\t");//不自动换行if(num%3==0){System.out.println();}}}System.out.println();System.out.println("--------------");//打印九九乘法表for(int i=1;i<=9;i++){for(int j=1;j<=i;j++){System.out.print(i+"*"+j+"="+i*j+"\t");}System.out.println();}}
   }

2. 增强for循环

   package com.kuang.struct;public class ForDemo08 {public static void main(String[] args) {//增强for循环int[] numbers={1,2,3,4,5};for(int x:numbers){System.out.println(x);}/*效果完全等同for(int i=0;i<5;i++){System.out.println(numbers[i]);}*/}
   }