Java Reference
In-Depth Information
TIP: Repeat N Times Loops
The simplest way to produce a loop that repeats the loop body a predetermined num-
ber of times is with a for statement. For example, the following is a loop that repeats
its loop body three times:
for ( int count = 1; count <= 3; count++)
System.out.println("Hip, Hip, Hurray");
The body of a for statement need not make any reference to a loop control variable,
such as the variable count .
PITFALL: Extra Semicolon in a for Statement
You normally do not place a semicolon after the closing parenthesis at the beginning
of a for loop. To see what can happen, consider the following for loop:
Problem
semicolon
for ( int count = 1; count <= 10; count++);
System.out.println("Hello");
If you did not notice the extra semicolon, you might expect this for loop to write
Hello to the screen 10 times. If you do notice the semicolon, you might expect the
compiler to issue an error message. Neither of those things happens. If you embed this
for loop in a complete program, the compiler will not complain. If you run the pro-
gram, only one Hello will be output instead of 10 Hellos. What is happening? To
answer that question, we need a little background.
One way to create a statement in Java is to put a semicolon after something. If you
put a semicolon after number++ , you change the expression
number++
into the statement
number++;
If you place a semicolon after nothing, you still create a statement. Thus, the
semicolon by itself is a statement, which is called the empty statement or the null
statement . The empty statement performs no action, but still is a statement. There-
fore, the following is a complete and legitimate for loop, whose body is the empty
statement:
empty
statement
null
statement
for ( int count = 1; count <= 10; count++);
(continued)
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