Strings - Beginning Java 8 Fundamentals - page 394

Strings in a switch Statement
I discussed the switch statement in Chapter 5. Java 7 added support for strings in a switch statement. The
switch -expression uses a String type. If the switch -expression is null , a NullPointerException is thrown. The case
labels must be String literals. You cannot use String variables in the case labels. The following is an example of using
a String in a switch statement, which will print "Turn on" on the standard output:

String status = "on";
switch(status) {
case "on":
System.out.println("Turn on"); // Will execute this
break;
case "off":
System.out.println("Turn off");
break;
default:
System.out.println("Unknown command");
break;
}

The switch statement for strings compares the switch -expression with case labels as if the equals() method
of the String class has been invoked. In the above example, status.equals("on") will be invoked to test if the first
case block should be executed. Note that the equals() method of the String class performs a case-sensitive string
comparison. It means that the switch statement that uses strings is case-sensitive.
The following switch statement will print "Unknown command" on the standard output, because the
switch-expression "ON" in uppercase will not match the first case label "on" in lowercase.

String status = "ON";
switch(status) {
case "on":
System.out.println("Turn on");
break;
case "off":
System.out.println("Turn off");
break;
default:
System.out.println("Unknown command"); // Will execute this
break;
}

As good programming practice, you need to do the following two things before executing a switch statement
with strings:

switch -expression for the switch statement is null . If it is null , do not execute
the switch statement.

• Check if the

switch statement, you need to
convert the switch -expression to lowercase or uppercase and use lowercase or uppercase in
the case labels accordingly.

• If you want to perform a case-insensitive comparison in a

You can rewrite the above switch statement example as shown in Listing 11-3, which takes care of the above
two suggestions.