Java Language Basic Control Structures Switch statement
Example
The switch statement is Java's multi-way branch statement. It is used to take the place of long if-else if-else chains, and make them more readable. However, unlike if statements, one may not use inequalities; each value must be concretely defined.
There are three critical components to the switch statement:
case: This is the value that is evaluated for equivalence with the argument to theswitchstatement.default: This is an optional, catch-all expression, should none of thecasestatements evaluate totrue.- Abrupt completion of the
casestatement; usuallybreak: This is required to prevent the undesired evaluation of furthercasestatements.
With the exception of continue, it is possible to use any statement which would cause the abrupt completion of a statement. This includes:
breakreturnthrow
In the example below, a typical switch statement is written with four possible cases, including default.
Scanner scan = new Scanner(System.in);
int i = scan.nextInt();
switch (i) {
case 0:
System.out.println("i is zero");
break;
case 1:
System.out.println("i is one");
break;
case 2:
System.out.println("i is two");
break;
default:
System.out.println("i is less than zero or greater than two");
}
By omitting break or any statement which would an abrupt completion, we can leverage what are known as "fall-through" cases, which evaluate against several values. This can be used to create ranges for a value to be successful against, but is still not as flexible as inequalities.
Scanner scan = new Scanner(System.in);
int foo = scan.nextInt();
switch(foo) {
case 1:
System.out.println("I'm equal or greater than one");
case 2:
case 3:
System.out.println("I'm one, two, or three");
break;
default:
System.out.println("I'm not either one, two, or three");
}
In case of foo == 1 the output will be:
I'm equal or greater than one
I'm one, two, or three
In case of foo == 3 the output will be:
I'm one, two, or three
Java SE 5
The switch statement can also be used with enums.
enum Option {
BLUE_PILL,
RED_PILL
}
public void takeOne(Option option) {
switch(option) {
case BLUE_PILL:
System.out.println("Story ends, wake up, believe whatever you want.");
break;
case RED_PILL:
System.out.println("I show you how deep the rabbit hole goes.");
break;
}
}
Java SE 7
The switch statement can also be used with Strings.
public void rhymingGame(String phrase) {
switch (phrase) {
case "apples and pears":
System.out.println("Stairs");
break;
case "lorry":
System.out.println("truck");
break;
default:
System.out.println("Don't know any more");
}
}
