Computer Programming Java VARIABLES.pptx

Java Variables
Variables are containers for storing data
values.
In Java, there are different types of variables,
for example:
•String - stores text, such as "Hello". String
values are surrounded by double quotes
•int - stores integers (whole numbers),
without decimals, such as 123 or -123

Java Variables
•float - stores floating point numbers,
with decimals, such as 19.99 or -19.99
•char - stores single characters, such as
'a' or 'B'. Char values are surrounded by
single quotes
•boolean - stores values with two states:
true or false

Declaring (Creating) Variables
To create a variable, you must specify the type
and assign it a value:
Where type is one of Java's types (such as int or String), and variableName is
the name of the variable (such as x or name). The equal sign is used to assign
values to the variable.

Example
Create a variable called name of type String and assign
it the value "John".
Then we use println() to print the name variable:

Create a variable called myNum of
type int and assign it the value 15:

You can also declare a variable without
assigning the value, and assign the value
later:
Note that if you assign a new value to an existing variable, it will
overwrite the previous value:

Change the value of myNum from 15 to 20:

Final Variables
If you don't want others (or yourself) to overwrite
existing values, use the final keyword (this will declare
the variable as "final" or "constant", which means
unchangeable and read-only):

A demonstration of how to declare
variables of other types:

EXERCISE
•True or False:
To create a variable in Java, you
must specify the type first.

EXERCISE
• Create a variable named carName and
assign the value Volvo to it.

EXERCISE
•Create variable named
maxSpeed and assign value 120
to it.

JAVA PRINT VARIABLES
Display Variables
• The println() method is often used to
display variables.
• To combine both text and a variable, use
the + character:
String name = "John";
System.out.println("Hello " + name);
Example:

You can also use the + character to add a
variable to another variable:
String firstName = "John ";
String lastName = "Doe";
String fullName = firstName + lastName;
System.out.println(fullName);
Example:

For numeric values, the + character works as a
mathematical operator (notice that we
use int (integer) variables here):
Example:
int x = 5;
int y = 6;
System.out.println(x + y); // Print the value of x + y

EXERCISES:
1. What method is often used to print
variables?
2. Insert the missing parts to combine both
text and a variable.
String name = “John”;
System.out.println(“Hello” );

EXERCISES:
3. Display the sum of 5 + 10, using two variables: x
and y.
= ;
int y = 10;
System.out.println( x + y );

EXERCISES:
4. Create a variable called z, assign x + y to it, and
display the result.
int x = 5 ;
int y = 10;
= x + y;
System.out.println( );

Java Declare Multiple Variables
Declare Many Variables
• To declare more than one variable of the same type, you
can use a comma-separated list:
Example
• Instead of writing: You can simply write:
int x = 5; int x = 5, y=6, z=50;
int y = 6; System.out.println( x + y + z);
int z = 50;
System.out.println( x + y + z);

One Value to Multiple Variables
• You can also assign the same value to multiple
variables in one line:
• Example:
int x, y, z;
x = y = z = 50;
System.out.println(x + y + z);

Java Identifiers
•Identifiers
•All Java variables must
be identified with unique names.
•These unique names are called identifiers.
•Identifiers can be short names (like x and
y) or more descriptive names (age, sum,
totalVolume).

Note: It is recommended to use descriptive names in
order to create understandable and maintainable code:

The general rules for naming
variables are:
•Names can contain letters, digits, underscores, and dollar
signs
•Names must begin with a letter
•Names should start with a lowercase letter, and cannot
contain whitespace
•Names can also begin with $ and _
•Names are case-sensitive ("myVar" and "myvar" are
different variables)
•Reserved words (like Java keywords, such
as int or boolean) cannot be used as names

Computer Programming Java VARIABLES.pptx

True or False:
All java variables
must be identified
with unique names.

Create a variable
named maxSpeed
and assign the value
120 to it.

Java Variables - Examples
Real-Life Examples
• Often in our examples, we simplify
variable names to match their data
type (myInt or myNum for int types,
myChar for char types, and so on).
This is done to avoid confusion.

However, for a practical example of using variables, we
have created a program that stores different data about
a college student:

Calculate the Area of a Rectangle
In this real-life
example, we create
a program to
calculate the area
of a rectangle (by
multiplying the
length and width):

Computer Programming Java VARIABLES.pptx

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