The switch statement

If we have to realize a multiple-choice selection we can use several nested if-else statements. Java has also a specific statement that can be used in specific cases to realize in a simpler way a multiple-choice selection.

switch statement (version with break)

Syntax:

switch (expression) {
  case label-1: statements-1
                 break;
  ...
  case label-n: statements-n
                 break;
  default: default-statements
}

• expression is an expression of an integer type or of type char
• label-1,..., label-n are constant integer (or character) expressions; in other words, the expressions can contain only integer (or character) literals or constants that are initialized with constant expressions; the values of two different labels cannot coincide
• statements-1,..., statements-n and default-statements are arbitrary sequences of statements
• the default part is optional

Semantics:

1. First, expression is evaluated.
2. Then, the first i is found for which the value of label-i is equal to the value of expression.
3. If there is such an i, then statements-i are executed;
   otherwise default-statements are executed.
4. The execution continues with the statement immediately following the switch statement.

Example:

int i;
...
switch (i) {
  case 0: System.out.println("zero"); break;
  case 1: System.out.println("one"); break;
  case 2: System.out.println("two"); break;
  default: System.out.println("less than zero or greater than two");
}

When i is equal to 0 (respectively, 1, 2) then "zero" (respectively "one", "two") is printed; when i is less than 0 or greater than two, then "less than zero or greater than two" is printed.

Note: If we have more than one values of the expression for which we want to execute the same statements, we can group together different cases:

case label-1: case label-2: statements
                               break;