Day008 select structure (switch statement)

           switch Selection structure :
               Grammatical structure :
                  switch( expression ){
                      case Constant 1:
                          // sentence 1
                          break;
                      case Constant 2:
                          // sentence 2
                         break;
                      case Constant 3:
                          // sentence 3
                          break;
                      ..........
                      case Constant n:
                          // sentence n
                          break;
                      default:
                          // sentence m;
                          break;
              }
           The law of execution :
                   Match according to the value of the expression case The following constant values , After matching, execute the corresponding statement , After executing the corresponding statement , perform break, End the whole thing switch structure , So let's keep going switch Select the code after the structure
                   If the value of the expression does not match all constant values , Is executed default The words in it , Execute... After execution break Quit the whole switch Selection structure
        
           Be careful :
          1) The value of the expression can make int、short、byte、char、 Enumeration type 、String（JDK1.7 And later versions support ）
          2)case The following constant values cannot be the same
          3)default Statement can be omitted . If you write that the value of the expression does not match the value of all expressions , Is executed default The sentence in .default Statements can be written anywhere , Generally written in the book switch At the end of
          4)switch Choosing a structure can only deal with the problem of equivalence judgment
          5)break The function of the statement is to end the whole switch Selection structure , If there is a lack of , The code will continue to run down , Carry out the next case The sentence in , This phenomenon is called "case Penetration phenomenon ".case Penetration phenomenon can be used reasonably

Example

Use switch Select a structure to judge the day of the year ？

package cn.bdqn.Demo03;

import java.util.Scanner;

public class practice111 {

public static void main(String[] args) {

Scanner sc = new Scanner(System.in);

System.out.println(" Please enter the year ：");

int year = sc.nextInt();

//System.out.println(" The year is :");

System.out.println(" Please enter the month ：");

int month = sc.nextInt();

//System.out.println(" Month is :");

System.out.println(" Please enter the number of days ：");

int day = sc.nextInt();

//System.out.println(" Days are :");

int sumDay = 0;

// Use penetration , Give Way 12 The month is at the top , Down in turn , Avoid penetrating to the end

switch (month) {

case 12:

sumDay += 30;

case 11:

sumDay += 31;

case 10:

sumDay += 30;

case 9:

sumDay += 31;

case 8:

sumDay += 31;

case 7:

sumDay += 30;

case 6:

sumDay += 31;

case 5:

sumDay += 30;

case 4:

sumDay += 31;

case 3:

// Runnian can be divided by four , It cannot be divided by onehundred or fourhundred

if(year%4==0&&year%100!=0||year%400==0){

sumDay += 29;

}else{

sumDay += 28;

}

case 2:

sumDay += 31;

case 1:

// give an example : if 6 month 6 Japan , What is added in the following formula is 6, The added whole month has 1,2,3,4,5 five months , Only added in June 6 God

sumDay += day;

//default:

//System.out.println(" The format of the entered date is incorrect ");

//break;

}

System.out.println(year+" year "+month+" month "+day+" Japan "+" It's the third day of the year "+sumDay+" God ");

System.out.println(" This is the end of program execution ");

sc.close();

}

}

 

  Use switch Select the structure to judge which season of the year a month belongs to .（ spring, summer, autumn and winter ）

package cn.bdqn.Demo03;

public class practice22 {

public static void main(String[] args) {

int month = 9;

// Use penetration

switch (month) {

case 3:

// System.out.println(" In the spring ");

// break;

case 4:

// System.out.println(" In the spring ");

// break;

case 5:

System.out.println(" In the spring ");

break;

case 6:

// System.out.println(" In the summer ");

// break;

case 7:

// System.out.println(" In the summer ");

// break;

case 8:

System.out.println(" In the summer ");

break;

case 9:

// System.out.println(" In the fall ");

// break;

case 10:

// System.out.println(" In the fall ");

// break;

case 11:

System.out.println(" In the fall ");

break;

case 12:

// System.out.println(" In the winter ");

// break;

case 1:

// System.out.println(" In the winter ");

// break;

case 2:

System.out.println(" In the winter ");

break;

default:

System.out.println(" Month input error ");

break;

}

System.out.println(" The program is finished ");

}

}