2 data types and operators

8/12/2019 2 Data Types and Operators

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Data types andOperators by Komal Sangtani


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Topics to be covered: Primitive Datatypes, Declarations, Ranges Variable Names Conventions Numeric Literals, Character Literals String Literals

Arrays (One dimensional; two- dimensional)

Array of Object References Accessing arrays, manipulating arrays Enumerated Data Types Non-Primitive Datatypes Defining a class, variable and method in

Java Method Signature; method calls

Expressions in Java;

Introduction to variousoperators Assignment Operator Arithmetic Operators Relational Operators Logical Operators Conditional Operators Operator Precedence Implicit Type Conversions Upcasting and

downcasting Strict typing Type conversion


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Steps for writing & compiling prog.

Create source code file (call it for exampleHello.java).

To compile:

prompt >> javac MyFirstProgram.java This produces byte code file named

Hello. class To run:

prompt >> java MyFirstProgram


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Writing first class

File:- Hello.java public class Hello {

public static void main(String args[]){

System.out.println (Hello World..!); }

}


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How it works!


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Identifiers - symbolic names Identifiers are used to name classes, variables,

and methods Identifier Rules:

Must start with a "Java letter" A - Z, a - z, _, $, and Unicode letters

Can contain essentially any number of Javaletters and digits, but no spaces

Case sensitive!! Number1 and number1 are different!

Cannot be keywords or reserved words


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Program Building Blocks

The Statement Performs some action Terminates with a semicolon (;) Can span multiple lines


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Building Blocks - The Block The Block

0, 1, or more statements Begins and ends with curly braces { } Can be used anywhere a statement is allowed.


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Building Blocks - White Space Space, tab, newline are white space characters At least one white space character is required

between a keyword and identifier Any amount of white space characters are

permitted between identifiers, keywords,operators, and literals

To increase readability of your code, surroundoperators and operands with white space andskip lines between logical sections of program.


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Building Blocks - Comments Comments explain the program to yourself and others Block comments

Can span several lines

Begin with /* End with */ Compiler ignores all text between /* and */

Line comments Start with // Compiler ignores text from // to end of line


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Data Types, Variables, andConstants

Declaring Variables Primitive Data Types Initial Values and Literals String Literals and Escape Sequences Constants


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Data Types For all data, assign a name (identifier) and a data

type Data type tells compiler:

How much memory to allocate Format in which to store data Types of operations you will perform on data

Compiler monitors use of data Java is a "strongly typed" language

Java "primitive data types"byte, short, int, long, float, double, char, boolean


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Declaring Variables Variables hold one value at a time, but that value

can change Syntax:

dataType identifier;or

dataType identifier1,

identifier2, ; Naming convention for variable names:

first letter is lowercase embedded words begin with uppercase letter


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Integer Types - Whole NumbersType Size in bytes Minimum Value Maximum Value byte 1 -128 127short 2 -32,768 32,767int 4 -2, 147, 483, 648 2, 147, 483, 647long 8 -9,223,372,036,854,775,808 9,223,372,036,854,775,807

Example declarations:int testGrade;

int numPlayers, highScore, diceRoll;

short xCoordinate, yCoordinate;

byte ageInYears;

long cityPopulation;


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Floating-Point Data Types Numbers with fractional partsType Size in Bytes Minimum Value Maximum Value

float 4 1.4E-45 3.4028235E38double 8 4.9E-324 1.7976931348623157E308

Example declarations:float salesTax;

double interestRate;double paycheck, sumSalaries;


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char Data Type One Unicode character (16 bits - 2 bytes)Type Size in Bytes Minimum Value Maximum Value char 2 character character

encoded as 0 encoded as FFFF

Example declarations:char finalGrade;

char newline, tab, doubleQuotes;


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boolean Data Type Two values only:

true

false Used for decision making or as "flag" variables Example declarations:

boolean isEmpty;

boolean passed, failed;


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Assigning Values to Variables

Assignment operator = Value on the right of the operator is assigned to the

variable on the left Value on the right can be a literal (text representing a

specific value), another variable, or an expression (explained later)

Syntax:

dataType variableName =initialValue;

Or

dataType variable1 = initialValue1,

variable2 = initialValue2 , ;


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Literals

A Literal is the source code representation of afixed value; literals are represented directly inyour code without requiring computation

int, short, byte Optional initial sign (+ or -) followed by digits 0 9

in any combination. long

Optional initial sign (+ or -) followed by digits 0 9 inany combination, terminated with an L or l .

***Use the capital L because the lowercase l can be

confused with the number 1.
http://download.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.htmlhttp://download.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html


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Floating-Point Literals float Optional initial sign (+ or -) followed by a floating-

point number in fixed or scientific format,terminated by an F or f .

double Optional initial sign (+ or -) followed by a floating-

point number in fixed or scientific format.

Note: Commas, dollar signs, and percent signs (%)cannot be used in integer or floating-pointliterals


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char and boolean Literals char

Any printable character enclosed in single quotes A decimal value from 0 65535

'\m' , where \m is an escape sequence. For example,'\n' represents a newline, and ' \t' represents a tabcharacter.

boolean

true or falseSee Example 2.2 Variables.java


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Assigning the Values of OtherVariables

Syntax:

dataType variable2 =variable1;

Rules:1. variable1 needs to be defined before this

statement appears in the source code2. variable1 and variable2 need to be compatible

data types; in other words, the precision ofvariable1 must be lower than or equal to that of

variable2 .


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Compatible Data TypesAny type in right column can be assigned to type in left

column:

Data Type Compatible Data Typesbyte byteshort byte, shortint byte, short, int, charlong byte, short, int, long, char

float float, byte, short, int, long, chardouble float, double, byte, short, int, long, charboolean booleanchar char


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Escape Sequences To include a special character in a String , use an

escape sequenceCharacter Escape SequenceNewline \nTab \tDouble quotes \"Single quote \'Backslash \\Backspace \bCarriage return \rForm feed \f


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Operators

Operators are special symbols used for: mathematical functions assignment statements

logical comparisons Examples of operators:

3 + 5 // uses + operator 14 + 5 4 * (5 3) // uses +, -, * operators

Expressions : can be combinations of variables andoperators that result in a value


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Groups of Operators

There are 5 different groups of operators: Arithmetic Operators Assignment Operator Increment / Decrement Operators Relational Operators Logical Operators


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Assignment Operator

Syntax:

target = expression;

expression: operators and operands that evaluateto a single value--value is then assigned to target--target must be a variable (or constant)--value must be compatible with target's datatype


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Examples:

int numPlayers = 10; // numPlayers holds10numPlayers = 8; // numPlayers holds 8

int legalAge = 18;

int voterAge = legalAge;

The next statement is illegalint height = weight * 2; //weight is not

defined

int weight = 20;

and generates the following compiler error:illegal forward reference


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Arithmetic OperatorsOperator Operation

+ addition

- subtraction

* multiplication

/ division

% modulus(remainder afterdivision)


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Arithmetic/Assignment Operators

Java allows combining arithmetic andassignment operators into a single operator:

Addition/assignment += Subtraction/assignment = Multiplication/assignment =

Division/assignment /= Remainder/assignment %=


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Arithmetic/Assignment Operators

The syntax isleftSide Op= rightSide ;

This is equivalent to:leftSide = leftSide Op rightSide ;

x%=5; x = x % 5;

x*=y+w*z; x = x*(y+w*z);

Allways it is avariable identifier. It is an arithmetic

operator.

It is either a literal | a variable identifier | an expression.


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Example

int x = 3; int y = 5; boolean result ;

result = (x > y); now result is assigned the value false because 3

is not greater than 5


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Logical Operators

Symbol Name&& AND|| OR

! NOT

|| T FT T T

F T F

&& T FT T F

F F F

Page 36


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Exampleboolean x = true ;

boolean y = false ;boolean result;

result = (x && y);

result is assigned the value false

result = ((x || y) && x);(x || y) evaluates to true(true && x) evaluates to trueresult is then assigned the value true

O P d


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Operators Precedence

Parentheses (), inside-out

Increment/decrement ++, --, from left to right

Multiplicative *, /, %, from left to right

Additive +, -, from left to right

Relational , =, from left to right

Equality ==, !=, from left to right

Logical AND &&

Logical OR ||

Assignment =, +=, -=, *=, /=, %=


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Arrays An array is a list of similar things An array has a fixed:

name type length

These must be declared when the array is

created. Arrays sizes cannot be changed during the

execution of the code


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3 6 3 1 6 3 4 1myArray =

0 1 2 3 4 5 6 7

myArray has room for 8 elements

the elements are accessed by their indexin Java, array indices start at 0


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Declaring Arrays

int myArray[];declares myArray to be an array of integers

myArray = new int[8];

sets up 8 integer-sized spaces in memory,labelled myArray[0] to myArray[7]

int myArray[] = new int[8];

combines the two statements in one line


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Assigning Values

refer to the array elements by index to storevalues in them.myArray[0] = 3;

myArray[1] = 6;myArray[2] = 3; ...

can create and initialise in one step:

int myArray[] = {3, 6, 3, 1, 6, 3, 4, 1};


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Iterating Through Arrays

for loops are useful when dealing with arrays:

for (int i = 0; i < myArray.length; i++) {myArray[i] = getsomevalue();

}


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Arrays of Objects

So far we have looked at an array of primitivetypes.

integers could also use doubles, floats, characters

Often want to have an array of objects Students, Books, Loans

Need to follow 3 steps.


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Declaring the Array

1. Declare the array private Student studentList[];

this declares studentList

2 .Create the arraystudentList = new Student[10];

this sets up 10 spaces in memory that canhold references to Student objects

3. Create Student objects and add them to the array:studentList[0] = new Student("Cathy","Computing");


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Numeric Type Conversion

Consider the following statements:

byte i = 100;

long k = i * 3 + 4;double d = i * 3.1 + k / 2;


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Conversion RulesWhen performing a binary operation involving twooperands of different types, Java automaticallyconverts the operand based on the following rules:

1. If one of the operands is double, the other isconverted into double.2. Otherwise, if one of the operands is float, theother is converted into float.

3. Otherwise, if one of the operands is long, theother is converted into long.4. Otherwise, both operands are converted into int.


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Type Casting

Implicit castingdouble d = 3; (type widening)

Explicit castingint i = (int)3.0; (type narrowing)int i = (int)3.9; (Fraction part

is truncated)What is wrong? int x = 5 / 2.0;

Casting between char and


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Casting between char andNumeric Types

int i = ' a ' ; // Same as int i = (int) ' a ' ;

char c = 97; // Same as char c = (char)97;


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