The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
Unlike if-then
and if-then-else
statements, the switch
statement can have a number of possible execution paths. A switch
works with the byte
, short
, char
, and int
primitive data types. It also works with enumerated types (discussed in
Enum Types), the
String
class, and a few special classes that wrap certain primitive types:
Character
,
Byte
,
Short
, and
Integer
(discussed in
Numbers and Strings).
The following code example,
SwitchDemo
, declares an int
named month
whose value represents a month. The code displays the name of the month, based on the value of month
, using the switch
statement.
public class SwitchDemo { public static void main(String[] args) { int month = 8; String monthString; switch (month) { case 1: monthString = "January"; break; case 2: monthString = "February"; break; case 3: monthString = "March"; break; case 4: monthString = "April"; break; case 5: monthString = "May"; break; case 6: monthString = "June"; break; case 7: monthString = "July"; break; case 8: monthString = "August"; break; case 9: monthString = "September"; break; case 10: monthString = "October"; break; case 11: monthString = "November"; break; case 12: monthString = "December"; break; default: monthString = "Invalid month"; break; } System.out.println(monthString); } }
In this case, August
is printed to standard output.
The body of a switch
statement is known as a switch block. A statement in the switch
block can be labeled with one or more case
or default
labels. The switch
statement evaluates its expression, then executes all statements that follow the matching case
label.
You could also display the name of the month with if-then-else
statements:
int month = 8; if (month == 1) { System.out.println("January"); } else if (month == 2) { System.out.println("February"); } ... // and so on
Deciding whether to use if-then-else
statements or a switch
statement is based on readability and the expression that the statement is testing. An if-then-else
statement can test expressions based on ranges of values or conditions, whereas a switch
statement tests expressions based only on a single integer, enumerated value, or String
object.
Another point of interest is the break
statement. Each break
statement terminates the enclosing switch
statement. Control flow continues with the first statement following the switch
block. The break
statements are necessary because without them, statements in switch
blocks fall through: All statements after the matching case
label are executed in sequence, regardless of the expression of subsequent case
labels, until a break
statement is encountered. The program
SwitchDemoFallThrough
shows statements in a switch
block that fall through. The program displays the month corresponding to the integer month
and the months that follow in the year:
public class SwitchDemoFallThrough { public static void main(String[] args) { java.util.ArrayList<String> futureMonths = new java.util.ArrayList<String>(); int month = 8; switch (month) { case 1: futureMonths.add("January"); case 2: futureMonths.add("February"); case 3: futureMonths.add("March"); case 4: futureMonths.add("April"); case 5: futureMonths.add("May"); case 6: futureMonths.add("June"); case 7: futureMonths.add("July"); case 8: futureMonths.add("August"); case 9: futureMonths.add("September"); case 10: futureMonths.add("October"); case 11: futureMonths.add("November"); case 12: futureMonths.add("December"); break; default: break; } if (futureMonths.isEmpty()) { System.out.println("Invalid month number"); } else { for (String monthName : futureMonths) { System.out.println(monthName); } } } }
This is the output from the code:
August September October November December
Technically, the final break
is not required because flow falls out of the switch
statement. Using a break
is recommended so that modifying the code is easier and less error prone. The default
section handles all values that are not explicitly handled by one of the case
sections.
The following code example,
SwitchDemo2
, shows how a statement can have multiple case
labels. The code example calculates the number of days in a particular month:
class SwitchDemo2 { public static void main(String[] args) { int month = 2; int year = 2000; int numDays = 0; switch (month) { case 1: case 3: case 5: case 7: case 8: case 10: case 12: numDays = 31; break; case 4: case 6: case 9: case 11: numDays = 30; break; case 2: if (((year % 4 == 0) && !(year % 100 == 0)) || (year % 400 == 0)) numDays = 29; else numDays = 28; break; default: System.out.println("Invalid month."); break; } System.out.println("Number of Days = " + numDays); } }
This is the output from the code:
Number of Days = 29
In Java SE 7 and later, you can use a String
object in the switch
statement's expression. The following code example,
StringSwitchDemo
, displays the number of the month based on the value of the String
named month
:
public class StringSwitchDemo { public static int getMonthNumber(String month) { int monthNumber = 0; if (month == null) { return monthNumber; } switch (month.toLowerCase()) { case "january": monthNumber = 1; break; case "february": monthNumber = 2; break; case "march": monthNumber = 3; break; case "april": monthNumber = 4; break; case "may": monthNumber = 5; break; case "june": monthNumber = 6; break; case "july": monthNumber = 7; break; case "august": monthNumber = 8; break; case "september": monthNumber = 9; break; case "october": monthNumber = 10; break; case "november": monthNumber = 11; break; case "december": monthNumber = 12; break; default: monthNumber = 0; break; } return monthNumber; } public static void main(String[] args) { String month = "August"; int returnedMonthNumber = StringSwitchDemo.getMonthNumber(month); if (returnedMonthNumber == 0) { System.out.println("Invalid month"); } else { System.out.println(returnedMonthNumber); } } }
The output from this code is 8
.
The String
in the switch
expression is compared with the expressions associated with each case
label as if the
String.equals
method were being used. In order for the StringSwitchDemo
example to accept any month regardless of case, month
is converted to lowercase (with the
toLowerCase
method), and all the strings associated with the case
labels are in lowercase.
Note: This example checks if the expression in the switch
statement is null
. Ensure that the expression in any switch
statement is not null to prevent a NullPointerException
from being thrown.