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

COM S 207Literal, Operator, and Expression

Instructor: Ying Cai

Department of Computer ScienceIowa State Universityyingcai@iastate.edu

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 -123345 793450

Not OK 1,234 (comma not

allowed) $1234 ($ not allowed)

long int literal ending with l or

L 12345l or 12345L

double OK

0.354 1.234e25

(=1.234*1025) -100.23E-24

Not OK 1,234.34 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 2323223” “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 OperatorsResult 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 EnglishLike operators, expressions will typically have a result, the result will have a type, and there may be a side effectSimple 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 resultint oneThousand = 1000;

int oneMillion = 1000 * oneThousand;

int oneBillion = 1000 * oneMillion;

System.out.println(3 * oneBillion);

will print out -1294976296why?

the result (3 billion) overflows int capacitymaximum 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 anotherWidening 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 conversionsint count;

short pastCount;

count = pastCount; //allowed and conversion done

Promotiondouble result, sum;

int count;

sum = 24.32; count = 4;

result = sum/count; // count promoted to double

Casting: used for narrowing conversionsdouble money = 2000.234

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