每天都进步的课堂随笔Day03

Java Processing Control（流程控制）

1. user interaction Scanner （用户交互scanner）

2. sequential structrue (顺序结构)

3. case structrue(选择结构)

4. loop structrue(循环结构)

5. break&continue

6. practice

   Scanner

   java.util.Scanner

   通过Scanner类来获取用户的输入

   • 基本语法：

   Scanner s = new Scanner(System.in)
   

   • 通过Scanner类的next()与nextLine()方法获取输入的字符串，在读取前我们一般需要使用 hasNext()与hasNextLine()判断是否还有输入的数据

package com.example.demo08;
import java.util.Scanner;
public class demo08 {
    public static void main(String[] args) {
        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()){
            //use next method to receive
            String str = scanner.nextLine();
            System.out.println("输出人内容为：" + str);
        }
        //凡是属于IO流的类如果不关闭会一直占用资源，要养成好习惯用完就关掉
        scanner.close();
    }
}

package com.example.demo08;

import java.util.Scanner;

public class demo08 {

    public static void main(String[] args) {
        //we can input so many words,then get sum&avg, using enter key to confirm each num u input
        //to end input by inputting non-numeric num then execute output result
        Scanner scanner = new Scanner(System.in);
        //sum
        double sum = 0;
        //calculate how much num has inputted
        int m = 0;
        //verify if there is any input by loop then count for each sum;
        while(scanner.hasNextDouble()){
         double x = scanner.nextDouble();
         m = m+1;//m++
            sum = sum + x;
        }
        System.out.println(m+"个数的和为" + sum);
        System.out.println(m+"个数的平均值是" + (sum/m));
        scanner.close();

    }

}

顺序结构

• JAVA的基本结构就是顺序结构，除非特别指明，否则就按照顺序一句一句执行

• 顺序结构是最简单的算法结构

• 语句与语句之间，框与框之间是按从上到下的顺序进行的，它是由若干个依次执行的处理步骤组成的，它是任何一个算法都离不开的一种基本算法结构

选择结构

• if单选择结构
• if双选择结构
• if多选择结构
• 嵌套的if结构
• switch多选择结构

if单选择结构

public static void main(String[] args) {
      Scanner scanner = new Scanner(System.in);

      System.out.println("please input some content: ");
      String s = scanner.nextLine();
      //equals to confirm if there is any equal String
      if(s.equals("Hello")){
          System.out.println(s);
      }
      System.out.println("End");

      scanner.close();
  }

if双选择结构

public static void main(String[] args) {
    //a score greater than 60 marks a passing grade,if less than 60 marks a failed grade
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入成绩：  ");
        int score = scanner.nextInt();
        if(score > 60){
            System.out.println("及格");
        }else{
            System.out.println("不及格");
        }
        scanner.close();
    }

if多选择结构

Switch 多选择结构

• switch case here to verify a variable which equals to a series of values, and called each value branch

  switch (expression){
      case value :
          //sentence
          break;//alternative
      case value :
          //sentence
          break;//alternative
      default : //alternative
          //sentence
  }
  

  • Switch，the variable in switch could be:
    • byte/short/int/char
    • begin with SE 7
    • String was supported in Switch
    • meanwhile case table must be String constants & literals

public class demo08 {
//case 穿透 //switch 匹配一个具体的值
    public static void main(String[] args) {
      char grade = 'c';
      switch(grade){
          case 'A':
              System.out.println("perfect");
              break;
          case 'B':
              System.out.println("excellent");
          case 'c':
              System.out.println("good");
              break;
          default:
              System.out.println("unknown rank");
      }
    }