* swtjc stem * chapter 2-3 cg 29 java operators recall java’s programming components:...

***** SWTJC STEM *****

Chapter 2-3 cg 29

Java Operators

Recall Java’s programming components:

Packages - Collection of classes (Programs)

Classes - Collections of data and methods that operate on data

Methods - Collections of statements that operate on data

Variables - Store dataConstants - Store data that doesn’t changeLiterals - Explicit data like “Hello World”

***** SWTJC STEM ***** Expressions and Operators

• Expressions are segments of code that perform computations and return values. They are combinations of literals, variables, constants, and operators.

• An operator performs an action on variables, constants, and literals.

• Associated with an operator are one or two operands that receive the action of the operator.

• Unary operators act on only one operand.

• Example: -12, negation operator “-”

• Binary operators act on two operands.

• Example: 8 + 15, addition operator “+”

Chapter 2-3 cg 29


Chapter 2-3 cg 29

Unary Operators

• Unary operators support either prefix or postfix notation.

• Prefix notation means that the operator appears before its operand:

• operator operand• Example:

- i , negation operator “-” ++ i, shortcut increment operator

“++“• Postfix notation means that the operator appears after

its operand:

• operand operator• Example:

i ++, shortcut increment operator “++“


Chapter 2-3 cg 29

Binary Operators

• Binary operators use infix notation, which means that the operator appears between its operands:

• operand1 operator operand2

• Examples:

• i + j

• a / b

• x += 10


Chapter 2-3 cg 29

Basic Numeric Operators

Operator Use Description

+ +op Promotes op to int if it's a byte, short, or char

- -op Arithmetically negates op

Unary Operators (op is an operand)

Operator

+

-

*

/

%

Use

op1 + op2

op1 - op2

op1 * op2

op1 / op2

op1 % op2

Description

Adds op1 and op2

Subtracts op2 from op1

Multiplies op1 by op2

Divides op1 by op2

Computes the remainder of dividing op1 by op2

Binary Operators


Chapter 2-3 cg 30

Numeric Operator Examples

Declare Variables... int i = 37; int j = 42; double x = 27.475; double y = 7.22;

Adding... i + j is 79 x + y is 34.695

Subtracting... i - j is -5 x - y is 20.255 x - (-y) is 34.695

Multiplying... i * j is 1554 x * y is 198.3695

Dividing... i / j is 0 (integer division implied) x / y is 3.8054...

Computing the remainder... i % j is 37 , j % i is 5 x % y is 5.815

Mixing types...converts to double...

j + y is 49.22 i * x is 1016.58


Chapter 2-3 cg 30

Coding an expression - Examples

Example: Coding expressions

1. int thisDecade = 2000; byte decadeLength = 10; int nextDecade = thisDecade + decadeLength;

byte decadeLength = 10; assigns the value 10 to a 8-bit byte variable named decadeLength.

int thisDecade = 2000; assigns the value 2000 to a 32-bit integer variable named thisDecade.

int nextDecade = thisDecade + decadeLength; assigns the value 2010 to a 32-bit integer variable named nextDecade.


Chapter 2-3 cg 30

Coding an expression - Examples

• Examples: Expression coding continued . . .

2. float radius = 2.0f; float area = 3.14159f * radius * radius;

float radius = 2.0f; assigns the value 2.0 to a 32-bit (single precision) floating point variable named radius.

float area = 3.14159f * radius * radius; assigns the computed expression to a 32-bit (single precision) floating point variable named area.


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Shortcut Incr/Decr Operators

Shortcut Increment/Decrement Operators


++ (incr) op++ Increments operand op by 1; evaluates to the value of op before incrementing op

++ (incr) ++op Increments operand op by 1; evaluates to the value of op after incrementing op

-- (decr) op-- Decrements operand op by 1; evaluates to the value of op before decrementing op

-- (decr) --op Decrements operand op by 1; evaluates to the value of op after decrementing op

Note: --i and i– (decrement) work similarly.


Chapter 2-3 cg 29

Shortcut Incr/Decr Examples

i newNum

Before 10 Undeclared

After 11 100

Postfix Operator Code... int i = 10;int newNum = 10 * (i++);

i increments after *.

Prefix Operator Code... int i = 10;int newNum = 10 * (++i);

i newNum

Before 10 Undeclared

After 11 110

i increments before *.


Chapter 2-3 cg 29

Shortcut Assignments Operators

Operator Use Equivalent to

+= op1 += op2 op1 = op1 + op2

-= op1 -= op2 op1 = op1 - op2

*= op1 *= op2 op1 = op1 * op2

/= op1 /= op2 op1 = op1 / op2

%= op1 %= op2 op1 = op1 % op2

Examples . . . iValue += 8; is the same as iValue = iValue + 8; jValue %= 5; is the same as jValue = jValue % 5;


Chapter 2-3 cg 29

Shortcut Assignment Examples

Assignment Addition Code: int i = 10; int newNum = 10; newNum += i; Same as newNum = newNum + i; newNum becomes 20. i remains 10.

Assignment Division Code: int i = 10; int newNum = 10; newNum /= i; Same as newNum = newNum / i; newNum becomes 1. i remains 10.


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Character Operator


+ char1 + char2string1 + string 2

Concatenates characters and strings

Binary Operator

• A char/string variable holds character/string data, respectively.

• Char literals use apostrophes ‘s‘ and are single values.• String literals use quotation marks “red leaf” and can hold

more than one character (i.e., text).• Concatenation “ties together” char/string variables and

literals.


Chapter 2-3 cg 29

Character Operator Examples

Examples . . .• char cValue = ‘s’;

Declares a character variable cValue and assigns character s to it.

• String c1Value = “red”, c2Value = “bird”; Declares string variables c1Value and c2Value assigning strings “red” and “bird” to them respectively.

• System.out.println(c1Value + c2Value + cValue); Outputs string redbirds to the PC monitor, which is the concatenation of all three variables.


Chapter 2-3 cg 29-31

Creating Complex Assignments

• When creating complex assignment expressions,

1. How is the order of operations determined?

2. What if we mix data and variable types?

• Examples:

• int result = 14 + 8 / 2; Is the result 11 (+ first)? or 18 (/ first)?

• int result = 12 / 2 * 3; Is the result 18 (/ first)? or 2 (* first)?

• float total = 100.46f;int count = 10;float result = total / count; // Mixed types? Is result 10 (integer /)? or 10.046 (float /)?



Order of Operations - Precedence

• Expressions are evaluated according to operator precedence.

• When operators of equal precedence occur together in an expression, association governs the order.

• Left-associative means operations are performed left-to-right.

Binary operators, except the assignment operator, are left-associative.

• Right-associative means operations are performed right-to-left.

Unary and assignment operators are right-associative.



Order of Operations - Precedence

Precedence Level

Operator Operation Associates

1 +

-

++,--

unary plus

unary minus

shortcut

R to L

2 */

%

multiplicationdivision

modulus

L to R

3 +

-

+

addition

subtraction

concatenation

L to R

4 =

+=,-=,...

assignment R to L



Order of Operations - Examples

• Given differing orders of precedence.

• result = 14 + 8 / 2; // Divide first

• / higher precedence than + and result is 18.

• Precedence can be forced using parentheses.

• result = (14 + 8) / 2; // Add first

• + is forced first by parentheses and result is 11.

• Given the same order of precedence.

• result = 12 / 2 * 3; // Divide first

• / is first (L to R), then * and result is 18.

• Adding a unary operator -.

• result = 12 / -(-3 + 1) * 3; // Negation first

• - is first (R to L), then / (L to R), then * and result is 18.



Order of Operations - Assignment

• Given assignment operators. Assume int a = 1.

1. result = a + (a = 3);

1) Proceed L to R a = 1, then 1 + (a = 3).

2) Now do (a = 3) then 1 + 3 result = 4.

2. result = (a = 3) + a;

1) Proceed L to R (a = 3) first, so a is now 3.

2) Now do a + a = 3 + 3 so result is 6.

3. result = (a += 2 * a) + a

1) (a = 1 + 2 * 1) + a.

2) (a = 3) + a = a + a = 3 + 3 = 6.



Order of Operations - Incr/Decr

• Given increment/decrement operators. Assume int a = 5.1. result = a + (--a) + a

1) Proceed L to R a = 5, then 5 + (--a) + a.2) Now do a = a - 1= 4 a, then 5 + 4 + a 9 + a.3) Finally, a = 4 and 9 + 4 result is 13.

2. result = a + (a--) + a1) Proceed L to R a = 5, then 5 + (a--) + a.2) Now do 5 + 5 + a = 10 + a, then do a = a - 1 = 4 a.3) Finally 10 + a = 10 + 4 result is 14.


Chapter 2-3 cg 32

Mixed Data/Variable Types

• Java is a strong typed language, meaning that all data and variables must be explicitly typed.

• Sometimes conversion is necessary.• Recall

float total = 100.46f;int count = 10;float result = total / count; // Mixed types?

• Care must be exercised or information can be lost.• byte a = 20; // 1 byte in size

int b = 2 * a ; // 4 bytes in sizeb can hold a; (1 byte) will fit in (4 bytes).

• int a = 2000; // 4 bytes in sizebyte b = 2 * a ; // 1 byte in sizeb cannot store a. ; (4 bytes) will not fit in (1 byte)!


Chapter 2-3 cg 32


• Conversions are of two types:

1. Widening conversions.

• Safest, does not lose information.

• Data conversion involves smaller to larger storage.

doublefloat

float, doublelong*

long, float, doubleint

int, long, float, doublechar

int, long, float, doubleshort

short, int, long, float, doublebyte

ToFrom

* Some precision (significant digits) could be lost!


Chapter 2-3 cg 32


• Conversions are of two types (continued):

2. Narrowing conversions.

• Likely to lose information. Avoid!

• Data conversion involves larger to smaller storage.

byte, short, char, int, longfloat

byte, short, char, intlong

byte, short, charint

byte, shortchar

byte, charshort

charbyte

ToFrom

byte, short, char, int, long, floatdouble


Chapter 2-3 cg 32

Assignment Conversion

• Java conversions occur in three ways:

1. Assignment conversion

• Occurs when one type is assigned to another.

• Only widening conversions allowed.

• Is automatic.

• double money;int dollars = 1000;money = dollars; // int will fit in doubleOK - Widening conversion, done.

• double money = 1000;byte dollars;dollars = money; // double will not fit in int (max 255)!Not OK - Narrowing conversion, error!


Chapter 2-3 cg 32

Arithmetic Promotion

• Java conversion occur in three ways (cont.):

2. Arithmetic promotion

• Occurs in expressions when operators need to widen (promote) data to complete.

• Only widening conversions allowed.

• Promotion is automatic when possible.

• float total = 100.46f, result;int count = 10;result = total / count; count promoted to float automatically.Floating point division used to calculate result.result is 1.0046.


Chapter 2-3 cg 32

Casting - Forced Conversion

• Java conversion can occur in three ways:

3. Casting - Forcing the conversion

• Most general form of conversion.

• Unary operator specified by a data type in parentheses, (type) operand.

• Is not automatic. Programmer must specify.

• Example:float money = 8.75f;int dollars;dollars = (int) money;Casts money (float) to dollars (int).dollars is 8money truncated (decimal portion dropped)


Chapter 2-3 cg 32

Casting Continued


3. (cont) Casting examples

• double result;int count = 10, total = 20;result = (double) total / count;

total cast to double.count automatically promoted to double.Floating point division used.Quotient 2.0 stored in result as a double.


Chapter 2-3 cg 32

Casting Continued


3. (cont) Casting char variables

• char c = 'A'; // upper case Aint ic;ic = (int) c;char c is cast as an int ic is 65.

• ic = 97;c = (char) ic;int ic is cast as char c = ‘a’, lower case a.

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