A switch statement allows a variable to be tested for equality against a list of values. Each value is called a case, and the variable being switched on is checked for each case. As such, it often provides a better alternative than a large series of if-else-if statements. Here is the general form of a switch statement:
switch (expression) {
case value1:
// statement sequence
break;
case value2:
// statement sequence
break;
.
.
.
case valueN :
// statement sequence
break;
default:
// default statement sequence
}Each value specified in the case statements must be a unique constant expression (such as a literal value). Duplicate case values are not allowed. The type of each value must be compatible with the type of expression.
The break statement is used inside the switch to terminate a statement sequence. When a break statement is encountered, execution branches to the first line of code that follows the entire switch statement.
If none of the constants matches the value of the expression, then the default statement is executed. However, the default statement is optional. If no case matches and no default is present, then no further action is taken.
// A simple example of the switch.
class SampleSwitch {
public static void main(String args[]) {
for(int i=0; i<6; i++)
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;
case 3:
System.out.println("i is three.");
break;
default:
System.out.println("i is greater than 3.");
}
}
}i is zero.
i is one.
i is two.
i is three.
i is greater than 3.
i is greater than 3.
The break statement is optional. If you omit the break, execution will continue on into the next case. It is sometimes desirable to have multiple cases without break statements between them.
class Switch {
public static void main(String args[]) {
int month = 3;
String season;
switch (month) {
case 12:
case 1:
case 2:
season = "Winter";
break;
case 3:
case 4:
case 5:
season = "Spring";
break;
case 6:
case 7:
case 8:
season = "Summer";
break;
case 9:
case 10:
case 11:
season = "Autumn";
break;
default:
season = "Bogus Month";
}
System.out.println("April is in the " + season + ".");
}
}March is in the Spring
You can use a switch as part of the statement sequence of an outer switch. This is called a
nested switch. Since a switch statement defines its own block, no conflicts arise between the case constants in the inner switch and those in the outer switch.
In summary, there are three important features of the switch statement to note:
- The
switchdiffers from theifin thatswitchcan only test for equality, whereasifcan evaluate any type ofBooleanexpression. That is, theswitchlooks only for a match between the value of the expression and one of itscaseconstants. - No two
caseconstants in the sameswitchcan have identical values. Of course, aswitchstatement and an enclosing outerswitchcan havecaseconstants in common. - A
switchstatement is usually more efficient than a set of nestedifs