Fall-Through Behavior of "switch" Statements

Java Tutorials - Herong's Tutorial Examples

∟Fall-Through Behavior of "switch" Statements

This section provides a tutorial example that show the 'fall-through' behavior of 'switch' statements.

From the previous tutorial, we learned that the execution of a "switch" statements starts from the label in the contained statement block that matches the value of a given test expression. The execution continues with all remaining sub-statements in the block, including "case" or "default" labels.

This behavior is called "fall-through" execution. If you do not want the execution falling through labels, you need to use "break" statements to jump out of the block.

Here is nice example from the Java language specification that demonstrate the "fall-through" behavior:

/* TooMany.java
 * From "The Java Language Specification"
 */
class TooMany {
  static void howMany(int k) {
    switch (k) {
      case 1: System.out.print("one ");
      case 2: System.out.print("too ");
      case 3: System.out.println("many");
    }
  }
  public static void main(String[] args) {
    howMany(3);
    howMany(2);
    howMany(1);
  }
}

The output confirms the fall-through behavior:

herong> java TooMany.java

many
too many
one too many

Here is the version that stops the fall-through behavior with "break" statements:

/* TwoMany.java
 * From "The Java Language Specification"
 */
class TwoMany {
  static void howMany(int k) {
    switch (k) {
      case 1: System.out.println("one");
        break;  // exit the switch
      case 2: System.out.println("two");
        break;  // exit the switch
      case 3: System.out.println("many");
        break;  // not needed, but good style
    }
  }
  public static void main(String[] args) {
    howMany(1);
    howMany(2);
    howMany(3);
  }
}