Java switch case statement

Sometime you may require to select one block of code from multiple block of code. To address such requirements java provides switch statement which allows java programmers to select one block from multiple block of statements. The syntax of switch statement is:

 switch (expression)
   {
     case constant-1:
         // code of case 1 block 
         break;
     case constant-2:
         // code of case 2 block
         break;
     case constant-3:
         // code of case 3 block
         break;
     . . . 
     . . . 
     case constant-N:
         // code of case N block
         break;    
     default:
        // code of default block
   }

switch statement evaluates it's expression and then selects the matching block. The working of switch statement is very similar to if-else if ladder, which means the same thing can be achieved using if-else if statement.

A programmer should remember below points while using switch statement in java.

• The expression used in a switch statement should be of type byte, short, char, int, enums and String(Java SE 7 and above). Wrapper classes Character, Byte, Short and Integer can also be used.
• A programmer can have any number of case statements within a switch block. Each case statement must be followed by the value to be compared to and a colon(:).
• Each case value must be unique. Duplicating a case value will result in compile time error.
• The type of value for every case must be same as data type of switch statement expression. Each case value must be a constant or a literal. You can not use variables, for example case num1, case num2 are incorrect declaration.
• There can be multiple lines of code(statements) for each case.
• When a case is matched, all the statements of that case will execute until a break statement is reached.
• When a break statement is reached, the switch block terminates, and the flow of control jumps to the next line after the switch block.
• Use of break statement is optional, If not used, all the cases(including codes inside it) after the matching case will execute until a break statement or end of switch statement is reached.
• The default case in switch statement is optional. It can be used to perform any tasks when no cases is matched.

Control flow diagram of switch statement

The above diagram shows the control flow of switch statement assuming that you have used break statement in every case of switch block

switch case program in Java

 class SwitchStatement
   {
     public static void main(String [] args)
       {          
          int dayNo = 4;     
	  String dayName;  
          switch (dayNo)
            {
              case 1:
                dayName = "Sunday";
                break;
              case 2:
                dayName = "Monday";
                break;
              case 3:
                dayName = "Tuesday";
                break;
              case 4:
                dayName = "Wednesday";
                break;
              case 5:
                dayName = "Thursday";
                break;
              case 6:
                dayName = "Friday";
                break;
              case 7:
                dayName = "Saturday";
                break;
              default: 
                dayName = "Invalid day";
                break;
            }
         System.out.println("day name = "+dayName);     
       }
   }

Output:

Programmer can decide whether to use if-then-else if or a switch statement on the basis of readability and the expression that the statement is testing. One example is, if-then-else if should be preferred when you want to test ranges of value like a>0 && a<10 while switch statement should be preferred to test single value like for a==5 execute this, for a==4 to execute that etc.