COMP 14 Introduction to Programming Miguel A Otaduy May 13 2004 Review Exercise Execution of c 2 a b in a computer Today in COMP 14 Java special symbols identifiers data types operators expressions Strings Reading Check Up syntax 1 The rules of a language determine which instructions are valid 2 True or False Hello is an example of False a legal Java identifier 3 If an operator has an integer and a floating point operand the result of floating point the operation is a number 4 The 9 expression int 9 2 evaluates to Introduction Computer program a sequence of statements whose objective is to accomplish a task Programming process of planning and creating a program Programming language a set of rules symbols and special words Sample Java Program public class Hello public static void main String args System out println Hi There Upon execution this program would display Hi There Programming Languages Programming languages have rules of grammar just as English does syntax rules which statements are legal and which are not semantic rules determine the meaning of the instructions token smallest individual unit of a program special symbols word symbols identifiers Special Symbols Word Symbols aka reserved words or keywords int float double char void public static throws return reserved words are always all lowercase each word symbol is considered to be a single symbol cannot be used for anything other than their intended purpose in a program shown in blue typewriter font in textbook full table in Appendix A Identifiers Names of things variables constants methods in your programs Can be composed of any combination of letters digits underscore and dollar sign Cannot begin with a digit May be any length Java is case sensitive Total total and TOTAL are different identifiers Illegal Identifiers Questions 1 2 3 4 5 6 Classify the following as legal or illegal identifiers My First Program illegal legal my1stProgram 1stProgram illegal money legal an identifier legal Jane sProgram illegal Primitive Data Types What s A Data Type A set of values and the operations that can be performed on those values Primitive data are fundamental values such as numbers and characters Operations are performed on primitive types using built in operators Primitive Data Types 8 primitive data types in Java 4 represent integers byte short int long 2 represent floating point numbers float double 1 represents characters char 1 represents boolean values boolean Primitive Data Types Numeric Types The difference between the various numeric primitive types is their size and therefore the values they can store Type byte short int long Storage 8 bits 16 bits 32 bits 64 bits float 32 bits double 64 bits Min Value 128 32 768 2 147 483 648 9 x 1018 Max Value 127 32 767 2 147 483 647 9 x 1018 3 4 x 1038 with 7 significant digits 1 7 x 10308 with 15 significant digits Integers Examples 6728 67 0 78 36782 Positive integers do not have a sign in front of them but they can No commas are used in an integer commas in Java are used to separate items in a list Primitive Data Types Characters A char stores a single character from the Unicode character set an ordered list of characters and each character corresponds to a unique number uses 16 bits per character allowing for 65 536 unique characters Character literals are delimited by single quotes a X 7 n newline character we ll discuss later Primitive Data Types Booleans Only two valid values true or false uses 1 bit for storage Represent any situation that has 2 states on off true false true and false are reserved words Arithmetic Expressions Expression a combination of one or more operands and their operators Arithmetic expressions compute numeric results and make use of the arithmetic operators Addition Subtraction Multiplication Division Remainder If either or both operands associated with an arithmetic operator are floating point the result is a floating point Division and Remainder If both operands to the division operator are integers the result is an integer the fractional part is discarded 14 3 equals 4 8 12 equals 0 The remainder or modulus operator returns the remainder after dividing the second operand into the first only works with integer types 14 3 equals 2 8 12 equals 8 Unary vs Binary Operators Unary operators has only one operand example negative not subtraction 5 Binary operators has two operands example subtraction 5 3 Operator Precedence Determines the order in which operators are evaluated 1 multiplication division and remainder 2 addition subtraction and string concatenation 3 arithmetic operators with the same precedence are evaluated from left to right Parentheses can be used to force the evaluation order just like in math Operator Precedence What is the order of evaluation in the following expressions a b c d e 1 2 3 4 a b c d e 3 1 4 2 a b c d e 2 1 4 3 a b c d e 4 3 2 1 Integral Expressions All operands are integers Result is an integer Examples 2 3 5 3 x y 7 x 2 y z 18 Floating point Expressions All operands are floating point numbers Result is a floating point Examples 12 8 17 5 34 50 x 10 5 y 16 2 7 0 3 5 Mixed Expressions Operands of different types Examples 2 3 5 2 0 3 5 6 4 3 9 1 3 9 1 0 3 9 Integer operands yield an integer result Floating point operands yield a floatingpoint result If both types of operands are present the result is a floating point number implicit type coercion Precedence rules are followed Type Conversion Casting Used to avoid implicit type coercion Syntax dataTypeName expression Expression evaluated first then type converted to dataTypeName Examples int 7 9 6 7 14 int 7 9 int 6 7 13 Questions Evaluate These Expressions 1 5 4 6 9 6 3 2 5 6 3 5 11 3 5 not possible 3 double 13 2 13 0 2 6 5 4 double 13 2 double 6 6 0 The class String 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 The class String is used to manipulate strings Examples Hello World 1234 45 67 Strings Every character has a position in the string starting with 0 Hello World 0123456789 The length of the string is the number of characters in it what s the length of Hello World 11 count the space Parsing Numeric Strings In Java input from the user comes in the form of a string we need to know how to get the number values out of the string Numeric String a string with only integers or decimal numbers 6723