Lab session 3 and 4

Lab sessionLab session3 and 43 and 4

Topics to be coveredTopics to be covered

• Escape sequences Escape sequences • Variables /identifiers Variables /identifiers • ConstantsConstants• assignment statementassignment statement• String concatenationString concatenation• String methodsString methods

ESCAPE SEQUENCESESCAPE SEQUENCES

• Java defines several Escape sequences to represent Special characters.

• An escape sequence begins with a backslash character (\) and indicates a character or characters that follow should be interpreted in some special way.

What does \t doWhat does \t do• \t - tab• When u use this in a println

statement • System.out.println(“Roses are red,\t Violets are blue,\t,Sugar is sweet”)

• OUTPUT

Roses are red, Violets are blue , Sugar is sweet

Escape Seq Meaning \b backspace \t tab \n newline \r carriage return \” Double quote \’ Single quote \\ backslash

What does \n doWhat does \n do

• \n - newline• When u use this in a println statement

• System.out.println(“Roses are red,\n Violets are blue,\n Sugar is sweet”);

OUTPUT

Roses are red, Violets are blue , Sugar is sweet

What does \” doWhat does \” do

• \n” - Double quote• When u use this in a println statement

• System.out.println(“\ Roses are red,\”Violets are blue”,\n Sugar is sweet”);

OUTPUT

Roses are red, “Violets are blue” , Sugar is sweet

What does \’ doWhat does \’ do

• \’ - Single quote• When u use this in a println statement

• System.out.println(“Roses are red, \‘Violets are blue\’Sugar is sweet.”);

OUTPUT

Roses are red, ‘Violets are blue’, Sugar is sweet.

What does \\ doWhat does \\ do

• \\ - backslash

• When u use this in a println statement

• System.out.println(“Roses are red\\Violets are blue\\Sugar is sweet.”);

OUTPUT

Roses are red\Violets are blue\Sugar is sweet.

What does \b doWhat does \b do

• \’ - backspace

• When u use this in a println statement

• System.out.println(“Roses are red, \bViolets are blue,\bSugar is sweet.”);

OUTPUT

Roses are red, Violets are blue,Sugar is sweet.

String ConcatenationString Concatenation• Strings that are printed using a print statement

can be concatenated using +

• Eg• System.out.println(“Roses are red”+“ ” +“Violets are blue” );

OUTPUT

Roses are red Violets are blue

VARIABLES /IDENTIFIERSVARIABLES /IDENTIFIERS• A Variable is a name for a location in

the memory used to hold a data value

num=25

25

num

memory

• Eg public class keys { Public static void main(String args[]) { int key ; //declaration statement key = 88; //initialization statement System.out.println(“A piano has” + key + “keys.”); System.out.println( key );} OUTPUT:

A piano has 88 keys 88

Primitive Data typePrimitive Data typeThere are 8 data types in java• Integer - has 4 subsets (byte, short, int,long)• Floating point numbers - 2 subsets ( float, double)• Boolean• Character

• Examples: • int num; // num can store whole numbers

• float average; // average can store decimal numbers

• char ch; // stores alphabets

• Boolean value; // stores either True/False

INTIALISATION STATEMENTINTIALISATION STATEMENT

• num=23;• average=23.00;• ch= ‘s’;• value=true;

Assignment statementAssignment statement• Assignment statement –assigns a value to a variable.Public class assign{Public static void main (String args[]){ int no; no=89; int num=56; //assignment st System.out.println(num); System.out.println (“The no is :“+no); }

Arithmetic expressionArithmetic expression• An expression is a combination of one or more

operators and operands• the basic arithmetic operations defined for integer type

and floating point type are• addition(+),subtraction(-,multiplication(*),division(/).• Java has one more arithmetic operation remainder(%)• 17%4 will return 1• a= b + c; a,b,c – operands + -- operator

Operator precedenceOperator precedence• Result=14+8/2; ans=18 ans=11

correct ans is 18

operator precedence hierarchy division/multiplication/% add/sub /concatenation

assignment

• Result=(14+8)/2; ans=11;

• result=((18-4)*(2+2)); =(14*4) = 56

expression should be syntactically correct no of left parenthesis should be =no of right parenthesis Result=((19+6)%3)*3); //invalid Result=2+8-6; usually u start from left when same level of precedence

objectsobjects• Class is used to define an object• Class name is nothing but type of object;• String name; //declaration 1st step• The above declaration creates a reference to

string object• No object actually exist• To create an obj use NEW operator:• name=new String (“Adam”); //obj created 2nd

step

• 1st and 2nd can be combined• String name=new String (“Adam”);• The String class has a no of methodsWhich its objects can useThey are

charat,replace,substring,length, toLowercase,toUppercase, concat,equals

String methodsString methods• String(String str)

• Constructor: creates a new string object with the same characters As str

• Eg String name=new String(“kenny”);Is eqvivalent to String name=“kenny”;

Length methodLength method• Int length ()

• Returns the no of characters in the string

• Eg String greeting= “Hello!”; greeting. length(); returns 7

LowercaseLowercase• String toLowerCase()

• Returns a new string identical to this string except all uppercase letters converted to lowercase

• Eg String greeting= “Hello!”; greeting. toLowerCase(); returns “hello!”.

UPPER CASEUPPER CASE• String toUpperCase()

• Returns a new string identical to this string except all lowercase letters converted to uppercase Eg

String greeting= “Hello!”; greeting. toLowerCase(); returns “HELLO!”.

TrimTrim• String trim()

• Returns a new string identical to this string but with leading and trailing white space removed

String pause= “ hhh “; pause. trim() returns “hhh”.

concatenationconcatenation• String concat(String str)

• Returns a new string consisting of this string concatenated with str

• Eg String name=new String (“kenny”); name.concat(“ is great “) returns “kenny is great”;

Char atChar at• Char charat(int index)

• Returns a character at specified index

• eg String name=new String (“kenny”); name.charat(0) returns ‘k’; name.charat(4) returns ‘y’;

SubstringSubstring• String substring(int start)

• Returns a substring of a string starting from index till end of this string.

• Eg String name=new String (“kenny”); name.substring(2) returns “nny”;

• String substring(int start,int end)

• Returns a substring of a string starting from index start through but not including index endof this string.

• Eg String name=new String (“kenny”); name.substring(2,4) returns “nn”;

ReplaceReplace• String replace(char old,char new)

Returns a new string identical to this string except that every occurrence of old is replaced by new.

• Eg String name=new String (“kenny”); name. replace (‘n’ ,’l’) returns “kelly”;

equalsequals

• Boolean equals(String str);

• Returns true if the string contains the same characters as str and false otherwise

(including case)

String greeting= “Hello!”; greeting. equals(“Hello”) returns true. but greeting. equals(“HELL0”) returns false

equalsIgnorecaseequalsIgnorecase• Boolean equalsIgnoreCase(String str);

• Returns true if the string contains the same characters as str and false otherwise

(without regard to case);

String greeting= “Hello!”;

greeting. equals(“HELL0”) returns true