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Graeme Kerry
is a first year computer systems engineering student
from the UK, studying at Lancaster University. He has been
programming in Java for about 3 years. Outside of studies
he enjoys sports and socialising with friends.
Kezz's Java Tutorials are written in Graeme's
spare time.
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If Statements
Welcome to the 4th installment of my Java programming tutorials.
In this tutorial I will discuss if statements and how they can be used
to implement decision making in your programs.
First of all lets have a look at an example of an if statement. This will show
you the syntax in Java.
if (age >= 18)
{
System.out.println("You are an adult");
}
else
{
System.out.println("You are a minor");
}
Just by looking at the code listed above it should
be pretty obvious as to what the code does. It checks the value of the variable
called age, if this is greater than or equal to 18 it prints "You are an adult",
and if it is less than 18 "You are a minor" will be printed.
This shows the general structure of an if-else statement in java:
if (condition)
{ //DO THIS }
else
{ //DO THIS }
A useful feature of if statements in java is that you
can nest them together to form complex decision making statements. The syntax
of this is listed below.
if (condition) { //DO THIS }
else if
(another condition) { //DO THIS }
else if (yet another
condition) { //DO THIS }
else { //FINALLY IF NONE OF THE ABOVE
CONDITIONS WERE MET DO THIS }
Finally for this tutorial I am going to go through
some special ways of using if statements and conditions. They are explained below
if (!condition)
This statement means if the condition is NOT
true. eg if (!(age==18)) means if the value of age is not 18
if ((condition1) && (condition2))
This statement means if condition 1 AND condition 2
are true. For example if ((if age>=18) && (gender.equals("male"))) translates to
if age is greater than or equal to 18 and the value of the string gender is male
The .equals(String) method is used for testing if 2 strings are equal, all other
variable types use ==.
if ((condition1) || (condition2)
This statement is very similar to the above one except
that the || means OR. So the statement translates to if condition1 OR condition2
are met
That's all folks....
I'm afraid there was a lot to take in in this tutorial (in very short space), however
you know what they say practice makes perfect. Thats why I have a small exercise for you:
You should now be able to write
a program that prompts the user for their name, age and gender and return it back
to them with additional information (eg whether its legal for them to drive yet
or what year they were born in). You should only prompt the user for those 3 pieces
of information and try and return as much info as you can from the details given.
If you have any trouble writing this or want to comment on the tutorials
email me
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