Constants and Variables
 Memory cells used in program
 Called constants and variables
 Identifiers for constants and variables should be
declared before the constants or variables are used
 Declaration is accomplished using declaration
statements
 Constants
 Values do not change during execution of the program
 Variables
 Values can be changed as the program executes.
Declarations of symbolic constants in Java
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Value of a constant can not change during the
execution of the program
Constant must be initialized when it is declared
Syntax of constant declaration
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final TYPE identifier = value;
OR
static final TYPE identifier = value;
Examples
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final float PI=3.141592654F;
static final double CONVERT=2.21;
Declarations of variables in Java
 A variable declaration assigns names for
variables (memory cells used in program)
 Syntax of variable declaration
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TYPE var_identifier;
or
TYPE var_identifier1=value, var_identifier2, …;
multiple variables of the same type may be declared
on the same line
Variable may be initialized when it is declared
Examples of Declaration of Variable Objects
 int my_integer_value;
 char middle_initial, first_initial;
 byte counter;
 double ScaleFactor;
 float temperature;
 Boolean TestResult
Initialization
 Memory locations associated with defined
constants must be initialized when the constants
are defined
 Memory locations associated with variables may
be initialized anywhere in the program
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Initialization may occur in the declaration statement
Initialization may be done after declaration using an
assignment statement
 Memory locations associated with variables
should have their values defined before they are
used.

It is good programming practice to initialize variables at
the start of your program
Examples: Initialization and Declaration
long my_integer_value = -12L;
 char myinitial = ′a′;
 byte counter = 31;
 short AgeInYears = 22;
 double ScaleFactor = 17.346798574;
 float temperature = 3.475F;
 boolean done_flag=false;

Data Types and Expressions
 Data Type
 A set of values plus a set of operations on those values
 A crucial concept on modern programming
 Data Type of a variable determines how its memory
cells are interpreted
 In Java every variable or constant object has a type
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Only values of that type can be directly assigned to the
variable.
Operators combine variables of the same type
Methods for implicit and explicit conversions between
types exist for specific conversions
Expressions
 An expression can be a single variable, or can include a series
of variables. If an expression includes multiple variables they
are combined using operators
 Arithmetic expressions manipulate numeric variables
following the rules of algebra and have numeric values.
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Integral expressions manipulate integer values
Floating point or decimal expressions manipulate floating point
numbers
 Relational expressions compare numerical values and have
logical (boolean) values
 Logical expressions combine boolean variables or expressions
and yield boolean values
Expressions
 An expression is a series of variables combined using
unary and/or binary operations
 An algebraic expression has a numeric value, a
relational or logical expression has a boolean value
 Example
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X*Y is an algebraic expression
If the variables X and Y have different types then they must
be converted to a common type before the expression X*Y
is evaluated
The type of the value of the entire expression is the same as
the common type the variables are converted to
Assignment Statements
 Basic statement using the assignment operator to set the value
of a variable to the value of an evaluated expression
 A way to save the results of evaluating an expression
 Form: resultvariable = expression;
 Examples:
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X = X + X * Y;
root = -3;
X += Y;
X -= 5;
 The types of the resultvariable and expression must be the
same.
Assignment operators
 A=B
assign value of expression B to
variable A, store result in A
 A += B
add the value of expression B to
variable A, store result in A
 A -= B
subtract the value of expression B
from variable A, store result in A
 A *= B
multiply the value of expression B
by variable A, store result in A
 A /= B
multiply the value of expression B
by variable A, store result in A
Rules for implicit conversion
 The value of the expression in an assignment
statement may be converted to the type of the
resultvariable
 The value of one of the operands of a binary
operation may be converted before the operation is
performed
 Some conversions are done implicitly. These
conversions are the widening conversions that always
have valid results
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byte to int
float to double
short to int
int to long
int to float
Explicit conversion: The cast operation
 In Java you can explicitly convert the type of a
variable or expression within a larger expression
using a cast operator
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The value of the variable or expression is not changed
The value used in the larger expression is converted to the
requested type
 Sample expressions including casts
 (int)(Floatone+Floattwo)
 (float)Integerone + Float1 + Float2
 (double)(int1)+double(short2) * double2
 (float)(int1)/int2