Lists, Logic, and Loops - Java 6 - page 91

The variable can be used only within that block. An error would result if you tried to use
the y variable in another part of the testBlock() method.

The x variable was created inside the method but outside the inner block, so it can be
used anywhere in the method. You can modify the value of x anywhere within the
method.

Block statements usually are not used alone within a method definition, as they are in the
preceding example. You use them throughout class and method definitions, as well as in
the logic and looping structures you learn about next.

if Conditionals
A key aspect of any programming language is how it enables a program to make deci-
sions. This is handled through a special type of statement called a conditional .

A conditional is a programming statement executed only if a specific condition is met.

The most basic conditional in Java is the if keyword. The if conditional uses a Boolean
expression to decide whether a statement should be executed. If the expression produces
a true value, the statement is executed.

Here's a simple example that displays the message “Not enough arguments” on only
one condition: If the value of the arguments.length instance variable is less than 3

4

if (arguments.length < 3)
System.out.println(“Not enough arguments”);

If you want something else to happen when an if expression produces a false value, an
optional else keyword can be used. The following example uses both if and else :

int duration;
if (arguments.length < 1)
“'“server = “localhost”;

else

“”server = arguments[0];

The if conditional executes different statements based on the result of a single Boolean
test.

A difference between if conditionals in Java and those in other
languages is that Java conditionals only produce Boolean values
( true or false ). In C and C++, the test can return an integer.

NOTE