Expressions
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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.
 Integral expressions manipulate integer values
 Floating point or decimal expressions manipulate floating point numbers
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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
 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
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
 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
Integral Expressions
► All
operands are integers
► Examples:
2+3*5
3 + x – y/7
x + 2 * (y – z) + 18
Floating-point Expressions
► All
operands are floating-point numbers
► Examples:
12.8 * 17.5 – 34.50
x * 10.5 + y - 16.2
Mixed Expressions
► Operands
of different types
► Examples:
2 + 3.5
6/4 + 3.9
► Integer operands yield an integer result; floating-point
numbers yield floating-point results
► If both types of operands are present, the result is a
floating-point number
► Precedence rules are followed
Initialization
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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
 Initialization may occur in the declaration statement
 Initialization may be done after declaration using an assignment
statement
 Initialization may also be done by ‘reading’ the value
►
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
Values and Memory Allocation for
Integral Data Types
The class String
► Used
to manipulate strings
► String
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Sequence of zero or more characters
Enclosed in double quotation marks
Null or empty strings have no characters
Numeric strings consist of integers or decimal
numbers
 Length is the number of characters in a string
Strings and the Operator +
► Operator
+ can be used to concatenate two strings or
a string and a numeric value or character
► Example:
Parsing Numeric Strings
► String
to int
Integer.parseInt(strExpression)
► String to float
Float.parseFloat(strExpression)
► String to double
Double.parseDouble(strExpression)
*strExpression: expression containing a numeric string
Input
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Standard input stream object: System.in
Input numeric data to program

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Separate by blanks, lines, or tabs
To read a line of characters:
Create an input stream object of the class
BufferedReader
2. Use the method readLine
1.
Input
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Standard input stream object: System.in
To read a line of characters: Create an input
stream object of the class BufferedReader
InputStreamReader charReader =
new InputStreamReader(System.in);
BufferedReader keyboard =
new BufferedReader(charReader):
►
Read the data into a variable of type string
inputStr = keyboard.readLine();
►
Parse the string
Output
► Standard
output object: System.out
► Methods
 print
 println
 flush
► Syntax
System.out.print(stringExp);
System.out.println(stringExp);
System.out.flush();
Commonly used escape sequences