COM S 207 Literal, Operator, and Expression Instructor: Ying Cai Department of Computer Science Iowa State University

Literals Literals are VALUES in a program int i = 10; char c = ‘A’; String s = “Hello”; In the above program, 10, ‘A’, and “Hello” are literals

datatype or type of a literal When Java sees a value, it DECIDES on a type for the literal 1234  Java will decide that this is an int type ‘a’  Java will decide that this is a char type true  Java will decide that this is a boolean type 2.3  Java will decide that this is a double type “Hi”  Java will decide that this is a String type The values will always be taken to be one of these types

Values must follow rules to be recognized int OK  1234   Not OK  1,234 (comma not allowed)  $1234 ($ not allowed) long int literal ending with l or L  12345l or 12345L double OK   1.234e25 (=1.234*10 25 )  E-24 Not OK  1,  1.23-e25 float double literals ending with f or F  0.23f or 0.23F

Values must follow rules to be recognized char single quote around a character  ‘a’, ‘A’, Not OK  ‘AB’ boolean only two valid value  true  false Not OK  TRUE  False  Yes  No  True  FALSE

String literals A String literal needs double quotes to surround them OK  “hello all”  “1234 hello ”  “a”  “a\””’

Arithmetic Operators These work with all primitive types except boolean + additive operator - subtraction operator * multiplication operator / division operator % remainder operator e.g., 5%2 = 1; 10%4 = 2; 10%6 =4 Result type depends on the type of the operand

Relational Operators Result type is boolean. Operands can be any primitive data type except boolean.

Boolean Operators Operands must be boolean. Result is of type boolean AND && OR (||) Reverse (!)

Assignment Operators “=“ is simple assignment operator It is different from “==“ which is a relational operator

++ Unary Operator ++i (pre increment) result value is new value side effect: 1 is added to value of I int i = 10; int k = ++i; // results: k=11 and i=11 i++ (post increment) result value is old value of I side effect: 1 is added to value of I int i = 10; int k = i++; // results: k=10 and i=11

Expressions Expressions are like clauses in sentences in English Like operators, expressions will typically have a result, the result will have a type, and there may be a side effect Simple expressions single operator and operands.  5/3, 5%3 method called  s.substring(0, 9)

Compound Expression Compound expressions are built from simple expressions (i >= 3) && (j/3 != 0) && (k < 5) i = j = 3 expression 1 expression 2 expressions

Precedence The order in which operations are done in an expression is defined by precedence of operators To avoid errors/confusing, using brackets ”()”

Associativity If we have operators with same precedence, which operation will be done first? This is known as “associativity” Associativity can be Right to Left (= operator) Left to Right (+ operator)

Storage per Type (in bytes)

Overflow Overflow occurs when the storage for a variable cannot hold the result int oneThousand = 1000; int oneMillion = 1000 * oneThousand; int oneBillion = 1000 * oneMillion; System.out.println(3 * oneBillion); will print out why? the result (3 billion) overflows int capacity maximum value for an int is +2,147,483,647 Use a long instead of an int (or use a double)

Data Conversion Converting one data type into another Widening conversion: no problem more space is available in the new type no data loss Narrowing conversion: problematic Less space is available in the new type data loss possible

Conversions Assignment for widening conversions int count; short pastCount; count = pastCount; //allowed and conversion done Promotion double result, sum; int count; sum = 24.32; count = 4; result = sum/count; // count promoted to double Casting: used for narrowing conversions double money = int handOver = (int) money; //thows away fraction

Special Conversion to String If one of the operands to the + operator is a String, the other operator is converted to a String and the two string are concatenated “hello” + 1  “Hello1” 1 + “hello”  “1Hello” This works for all types