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1.6 FizzBuzz Switched
Example 1-6 is another version of the
FizzBuzz game. This version uses a
switch statement instead of nested
if/else statements to determine what its output
should be for each number. Take a look at the example first, then
read the explanation of switch.
Example 1-6. FizzBuzz2.java
package je3.basics;
/**
* This class is much like the FizzBuzz class, but uses a switch statement
* instead of repeated if/else statements
**/
public class FizzBuzz2 {
public static void main(String[ ] args) {
for(int i = 1; i <= 100; i++) { // count from 1 to 100
switch(i % 35) { // What's the remainder when divided by 35?
case 0: // For multiples of 35...
System.out.print("fizzbuzz "); // print "fizzbuzz".
break; // Don't forget this statement!
case 5: case 10: case 15: // If the remainder is any of these
case 20: case 25: case 30: // then the number is a multiple of 5
System.out.print("fizz "); // so print "fizz".
break;
case 7: case 14: case 21: case 28: // For any multiple of 7...
System.out.print("buzz "); // print "buzz".
break;
default: // For any other number...
System.out.print(i + " "); // print the number.
break;
}
}
System.out.println( );
}
}
The switch
statement acts like a switch operator at a busy rail yard, switching
a train (or the execution of a program) to the appropriate track (or
piece of code) out of many potential tracks. A
switch statement is often an alternative to
repeated if/else statements, but it only works
when the value being tested is an integer (i.e.,
long, float,
double, boolean, and reference
types such as String objects are not allowed) and
when the value is being tested against constant values. The basic
syntax of the switch statement is:
switch(expression) {
statements
}The switch statement is followed by an
expression in parentheses and a block of
code in curly braces. After evaluating the
expression, the switch
statement executes certain code within the block, depending on the
integral value of the expression. How does the
switch statement know where to start executing
code for which values? This information is indicated by
case: labels and with the special
default: label. Each case:
label is followed by an integral value. If the
expression evaluates to that value, the
switch statement begins executing code immediately
following that case: label. If there is no
case: label that matches the value of the
expression, the switch statement starts executing
code following the default: label, if there is
one. If there is no default: label,
switch does nothing.
The switch statement is an unusual one because
each case doesn't have its own unique block of code.
Instead, case: and default:
labels simply mark various entry points into a single large block of
code. Typically, each label is followed by several statements and
then a break statement, which causes the flow of
control to exit out of the block of the switch
statement. If you don't use a
break statement at the end of the code for a
label, the execution of that case "drops
through" to the next case. If you want to see this
in action, remove the break statements from Example 1-6 and see what happens when you run the program.
Forgetting break statements within a
switch statement is a common source of bugs.
