Expressions An expression can be a single variable

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. ► § 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 § 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 § § § byte to int float to double short to 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 + Float 1 + Float 2 § (double)(int 1)+double(short 2) * double 2 § (float)(int 1)/int 2

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 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 § 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. parse. Int(str. Expression) ► String to float Float. parse. Float(str. Expression) ► String to double Double. parse. Double(str. Expression) *str. Expression: expression containing a numeric string

Input Standard input stream object: System. in ► Input numeric data to program ► § ► Separate by blanks, lines, or tabs To read a line of characters: 1. Create an input stream object of the class Buffered. Reader 2. Use the method read. Line

Input Standard input stream object: System. in ► To read a line of characters: Create an input stream object of the class Buffered. Reader ► Input. Stream. Reader char. Reader = new Input. Stream. Reader(System. in); Buffered. Reader keyboard = new Buffered. Reader(char. Reader): ► Read the data into a variable of type string input. Str = keyboard. read. Line(); ► Parse the string

Output ► Standard output object: System. out ► Methods § println § flush ► Syntax System. out. print(string. Exp); System. out. println(string. Exp); System. out. flush();

Commonly used escape sequences