"switch" Statements

Java Tutorials - Herong's Tutorial Examples

∟"switch" Statements

This section describes 'switch' statement, which is a decision-making statement that executes a portion of the contained statement block by passing control to a sub-statement based on label matching.

What Is "switch" Statement? - A "switch" statement is a decision-making statement that executes a portion of the contained statement block. The executed portion starts from a statement whose label matches a given expression value and ends with the last statement of the block.

Here is the syntax for a "switch" statement.

switch (test_expression) {
  case label_constant:
     sub-statement
     sub-statement
     ...
  case label_constant:
     sub-statement
     sub-statement
     ...
  default:
     sub-statement
     sub-statement
     ...
}

When a "switch" statement is executed, the test_expression is evaluated first. The resulting value is then compared with all label_constants. When a match is found, control is passed to the matching label. when no match is found, control is passed to the "default" label (if provided).

Here is a sample program that shows you how to use nested "if-then-else" statements:

/* SwitchStatementTest.java
 * Copyright (c) HerongYang.com. All Rights Reserved.
 */
import java.time.LocalTime;
class SwitchStatementTest {
   public static void main(String[] arg) {
      java.io.PrintStream out = System.out;
      LocalTime now = LocalTime.now();
      int hour = now.getHour(); // from 0 to 23

      out.println("\"switch\" statement:");
      int workingHours = 8;
      switch (hour) {
        case  9: workingHours--; // starts here when hour ==  9
        case 10: workingHours--; // starts here when hour == 10
        case 11: workingHours--; // starts here when hour == 11
        case 12: workingHours--; // starts here when hour == 12
        case 13: workingHours--; // starts here when hour == 13
        case 14: workingHours--; // starts here when hour == 14
        case 15: workingHours--; // starts here when hour == 15
        case 16: workingHours--; // starts here when hour == 16
      }
      out.println("   Worked "+workingHours+" full hours with no breaks!");
      out.println("   Current time is "+now);
   }
}

If you compile and run the above program, you will see:

herong> java SwitchStatementTest.java

"switch" statement:
   Worked 3 full hours with no breaks!
   Current time is 12:15:11.702155

As you can see from the output, the program executes the "switch" statement as below:

Evaluates the test expression "hour" to value "12".
Passes the control to the statement labeled with "case 12" in the contained statement block.
Runs all statements from "case 12" to the end of the block, that decrements "workingHours" 5 times.