Explain If Else Statement In Java With Program And Explanations, Program To Describe If Else Statement
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if statement is Java’s conditional branch statement. It can be used to route program execution through
two different paths. Here is the general form of the
if
statement:
if ( condition ) statement1 ;
else statement2 ;
Here, each statement may be a single statement or a compound statement enclosed in curly
braces (that is, a block ). The condition is any expression that returns a
boolean
value. The
else
clause is optional.
The
if
works like this: If the condition is true, then statement1 is executed. Otherwise,
statement2 (if it exists) is executed. In no case will both statements be executed. For example,
consider the following:
int a, b;
// ...
if(a < b) a = 0;
else b = 0;
Here, if
a
is less than
b
, then
a
is set to zero. Otherwise,
b
is set to zero. In no case are they
both set to zero.
Most often, the expression used to control the
if
will involve the relational operators.
However, this is not technically necessary. It is possible to control the
if
using a single
boolean
variable, as shown in this code fragment:
boolean dataAvailable;
// ...
if (dataAvailable)
ProcessData();
else
waitForMoreData();
Remember, only one statement can appear directly after the
if
or the
else
. If you want
to include more statements, you’ll need to create a block, as in this fragment:
int bytesAvailable;
// ...
if (bytesAvailable > 0) {
ProcessData();
bytesAvailable -= n;
} else
waitForMoreData();
Here, both statements within the
if
block will execute if
bytesAvailable
is greater than zero.
Some programmers find it convenient to include the curly braces when using the
if
,
even when there is only one statement in each clause. This makes it easy to add another
statement at a later date, and you don’t have to worry about forgetting the braces. In fact,
forgetting to define a block when one is needed is a common cause of errors. For example,
consider the following code fragment:
int bytesAvailable;
// ...
if (bytesAvailable > 0) {
ProcessData();
bytesAvailable -= n;
} else
waitForMoreData();
bytesAvailable = n;
It seems clear that the statement
bytesAvailable = n;
was intended to be executed inside
the
else
clause, because of the indentation level. However, as you recall, whitespace is
insignificant to Java, and there is no way for the compiler to know what was intended. This
code will compile without complaint, but it will behave incorrectly when run. The preceding
example is fixed in the code that follows:
int bytesAvailable;
// ...
if (bytesAvailable > 0) {
ProcessData();
bytesAvailable -= n;
} else {
waitForMoreData();
bytesAvailable = n;
}