java Control Statements

The if Statement
The Java if statement works much like the IF statement in any other language. Further,
it is syntactically identical to the if statements in C, C++, and C#. Its simplest form is
shown here:

if(condition) statement;

Here, condition is a Boolean expression. If condition is true, then the statement is
executed. If condition is false, then the statement is bypassed. Here is an example:
if(num < 100) println("num is less than 100");
In this case, if num contains a value that is less than 100, the conditional expression
is true, and println( ) will execute. If num contains a value greater than or equal to 100,
then the println( ) method is bypassed.
As you will see in other posts, Java defines a full complement of relational operators
which may be used in a conditional expression. Here are a few:
Operator Meaning
< Less than
> Greater than
== Equal to
Notice that the test for equality is the double equal sign.
Here is a program that illustrates the if statement:
/*
Demonstrate the if.
Call this file "IfSample.java".
*/
class IfSample {
public static void main(String args[]) {
int x, y;
x = 10;
y = 20;
if(x < y) System.out.println("x is less than y");
x = x * 2;
if(x == y) System.out.println("x now equal to y");
x = x * 2;
if(x > y) System.out.println("x now greater than y");

// this won't display anything
if(x == y) System.out.println("you won't see this");
}
}
The output generated by this program is shown here:
x is less than y
x now equal to y
x now greater than y
Notice one other thing in this program. The line
int x, y;
declares two variables, x and y, by use of a comma-separated list.
The for Loop
As you may know from your previous programming experience, loop statements are
an important part of nearly any programming language. Java is no exception. In fact,
as you will see in in other posts, Java supplies a powerful assortment of loop constructs.
Perhaps the most versatile is the for loop. If you are familiar with C, C++, or C#, then
you will be pleased to know that the for loop in Java works the same way it does in
those languages. If you don’t know C/C++/C#, the for loop is still easy to use. The
simplest form of the for loop is shown here:
for(initialization; condition; iteration) statement;
In its most common form, the initialization portion of the loop sets a loop control
variable to an initial value. The condition is a Boolean expression that tests the loop
control variable. If the outcome of that test is true, the for loop continues to iterate. If it
is false, the loop terminates. The iteration expression determines how the loop control
variable is changed each time the loop iterates. Here is a short program that illustrates

the for loop:
/*
Demonstrate the for loop.
Call this file "ForTest.java".

*/
class ForTest {
public static void main(String args[]) {
int x;
for(x = 0; x<10; x = x+1)
System.out.println("This is x: " + x);
}
}
This program generates the following output:
This is x: 0
This is x: 1
This is x: 2
This is x: 3
This is x: 4
This is x: 5
This is x: 6
This is x: 7
This is x: 8
This is x: 9
In this example, x is the loop control variable. It is initialized to zero in the initialization
portion of the for. At the start of each iteration (including the first one), the conditional
test x < 10 is performed. If the outcome of this test is true, the println( ) statement is
executed, and then the iteration portion of the loop is executed. This process continues
until the conditional test is false.
As a point of interest, in professionally written Java programs you will almost
never see the iteration portion of the loop written as shown in the preceding program.
That is, you will seldom see statements like this:
x = x + 1;
The reason is that Java includes a special increment operator which performs this
operation more efficiently. The increment operator is ++. (That is, two plus signs back
to back.) The increment operator increases its operand by one. By use of the increment
operator, the preceding statement can be written like this:

x++;
Thus, the for in the preceding program will usually be written like this:
for(x = 0; x<10; x++)
You might want to try this. As you will see, the loop still runs exactly the same as it
did before.
Java also provides a decrement operator, which is specified as – –. This operator
decreases its operand by one.