Switch case statement problem in Java

Usage of switch case statement in Java: 1. The switch statement can have multiple case statements; 2. The data type of the value in the case statement must be the same as the data type of the variable, and it can only be a constant or literal Constant; 3. When encountering a break statement, the switch statement terminates.

Usage of switch case statement in Java:

Syntax

## The syntax format of the #switch case statement is as follows:

switch(expression){
    case value :
       //语句
       break; //可选
    case value :
       //语句
       break; //可选
    //你可以有任意数量的case语句
    default : //可选
       //语句
}

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The switch case statement has The following rules:

• #The variable type in the switch statement can be: byte, short, int or char. Starting from Java SE 7, switch supports the String type, and the case label must be a string constant or literal.

• The switch statement can have multiple case statements. Each case is followed by a value to be compared and a colon.

• The data type of the value in the case statement must be the same as the data type of the variable, and it can only be a constant or literal constant.

• When the value of the variable is equal to the value of the case statement, the statements after the case statement begin to execute, and the switch statement will not be jumped out until the break statement appears.

• The switch statement terminates when a break statement is encountered. The program jumps to the statement following the switch statement for execution. The case statement does not have to contain a break statement. If no break statement occurs, the program continues execution of the next case statement until a break statement occurs.

• The switch statement can contain a default branch, which is generally the last branch of the switch statement (can be at any position, but it is recommended to be the last one). default is executed when no case statement is equal to the variable value. The default branch does not require a break statement.

• When the switch case is executed, it will be matched first. If the match is successful, the value of the current case will be returned. Then, based on whether there is a break, it will be judged whether to continue output or jump out of the judgment.

Example

Test.java file code:

public class Test {
   public static void main(String args[]){
      //char grade = args[0].charAt(0);
      char grade = 'C';
 
      switch(grade)
      {
         case 'A' :
            System.out.println("优秀"); 
            break;
         case 'B' :
         case 'C' :
            System.out.println("良好");
            break;
         case 'D' :
            System.out.println("及格");
            break;
         case 'F' :
            System.out.println("你需要再努力努力");
            break;
         default :
            System.out.println("未知等级");
      }
      System.out.println("你的等级是 " + grade);
   }
}

The results of compiling and running the above code are as follows:

良好
你的等级是 C

If there is no break statement in the case statement block, the JVM will not output the return value corresponding to each case sequentially, but will continue to match. If the match is unsuccessful, the default case will be returned.

Test.java file code:

public class Test {
   public static void main(String args[]){
      int i = 5;
      switch(i){
         case 0:
            System.out.println("0");
         case 1:
            System.out.println("1");
         case 2:
            System.out.println("2");
         default:
            System.out.println("default");
      }
   }
}

The compilation and running results of the above code are as follows:

default

If there is no break statement in the case statement block, it will match After success, starting from the current case, the values ​​of all subsequent cases will be output.

Test.java file code:

public class Test {
   public static void main(String args[]){
      int i = 1;
      switch(i){
         case 0:
            System.out.println("0");
         case 1:
            System.out.println("1");
         case 2:
            System.out.println("2");
         default:
            System.out.println("default");
      }
   }
}

The compilation and running results of the above code are as follows:

1
2
default

If the current successfully matched case statement block does not have a break statement, start from the current case , all subsequent case values ​​will be output, and if the subsequent case statement block has a break statement, the judgment will be jumped out.

Test.java file code:

public class Test {
   public static void main(String args[]){
      int i = 1;
      switch(i){
         case 0:
            System.out.println("0");
         case 1:
            System.out.println("1");
         case 2:
            System.out.println("2");
         case 3:
            System.out.println("3"); break;
         default:
            System.out.println("default");
      }
   }
}

The above code is compiled and run and the results are as follows:

1
2
3

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