Operations on Strings

8/8/2019 Operations on Strings

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Operations on String

Joining Strings

tring myString = The quick brown fox +

String date = 31st ;String month = December;String lastDay = date + month;// Result

String phrase = Toomany;


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Example I (String

JoinStrings.javaTestConcat.java

conc Concatenates 2


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The conversion of values ofthe basic types to type Stringis actually accomplished byusing a static method,toString(), of a standard class

that corresponds to the basictype (wrapper class).

BasicType

WrapperClass

byte Byte

short Shortint Integer

long Longfloat Float

double Double

boolean Booleanchar Character

The classes in the table are calwrapper classes because objects of eaof these class types wrap a value of tcorresponding primitive type. Whenevevalue of one of the basic types appears an operand to + and the other operand isString object, the compiler arranges pass the value of the basic type as targument to the toString() method thatdefined in the corresponding wrapp

String doubleString =Creates a String objefrom a value of any of t


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Operations on Strings

string1 ==Does not compare the strings themselvescompares the references to the strings, the result will be true only if string1 a

Example II (2 Strings, Identical but Not the

MatchStrings.java

Comparing Strings for Equalty

f (string1.equals(string3)) {

System.out.println(string1.equals(stringis true. + so strings are equal.);Does a case-sensitive comparison corresponding characters in the strings areturns true if the strings are equal; faotherwise. Two strings are equal if they are tsame length, i.e., have the same number


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This feature makes it possible

to compare strings with the== operator effective.

String interning ensures thatno 2 String objects

equalsIgnoreCCheck for equality betweenstrin s, i norin the case

Example III (String Identity)

MatchStrings2.javaequalsDemo.jav

aEqualsNotEqualT

String Interning


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encapsulate the same string,so all String objects

encapsulate unique strings.This means that if 2 Stringvariables reference stringsthat are identical, thereferences must be identical,

too.To arrange that all Stringobjects encapsulate uniquestrings, use intern().

tring string1 = Too many ;tring string2 = cooks;tring string3 = Too many cooks;

/ Make string1 and string3 refer to separatetrings that are identical

tring1 += string2;tring1 = string1.intern();// Intern string1

Checks the string referenced string1 against all the Strobjects currently in existence. Ialready exists, the current objwill be discarded, and string1 wcontain a reference to the existiobject encapsulating the samstring. As a result, the expressi


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All string constants andconstant String expressionsare automatically interned.

Benefits of string interning:-(i) Reduces the amount of

memory required forstoring String objects in

the program. If theprogram generates a lot ofduplicate strings then thiswill be significant.

Strin strin 4 = Too The reference stored string4 will be automaticathe same as the referen

strin 1 = (strin 1 +interns the result of texpression (string1 string2), ensuring that t


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(ii) Allows the use of ==instead of the equals()method when we want tocompare strings forequality. Since the ==operator just compares 2references, it will be much

faster than the equals()method, which involves asequence of character-by-character comparisons.

Checking the Start and End of a

tring string1 = Too many cooks;f (string1.startsWith(Too)) {

System.out.println(The string does startwith \Too\ too!);

Tests whether string starts with particular charactsequence


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string1.endsWith( Checks for whappears at the

end of a strinSe uencin Strin s

string1.compareTo(

Compares 2 strings by comparing successicorresponding characters, starting with t1st character in each string. The procecontinues until either correspondicharacters are found to be different, or t

last character in one or both strings reached. Characters are compared comparing their Unicode representations2 characters are equal if the numeric valuof their Unicode representations are equOne character is greater than another if t

SequenceStrings.javaSortString.java

Example IV (Ordering

Value

Meaning

< 0 Invoking string 0 Invoking string

int Case difference


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Extractin Strin

char charAt(int

StringCharacters.java

Example

V (Getting at Characters in a

Searchin Strin s or

int index = 0;// Position of character in the

string

Returns -1 o

search is

index = Searches the string backwards, startwith the last character in the string. The variable index therefore contains tindex position of the last occurrence of a,


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index = text.indexOf(a,Searches forwardsfrom a given positio

nt aIndex = -1;// Position of 1st ant bIndex = -1;// Position of 1st b afte

aIndex = text.indexOf(a);// Find firstaf (aIndex >= 0) {// Make sure you

Finds the 1st

that comes aft

the 1st

a in

int aIndex = -1;// Search startpositionint count = 0; // Count of aoccurrences

while ((aIndex = text.indexOf(a, +

Used to count homany times articular charact

Searchin or


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Method Description

indexOf(intch)

Returns the indexposition of the 1st

occurrence of thecharacter ch inthe String for

which the methodis called. If thecharacter ch doesnot occur, -1 isreturned.

indexOf(intch, intindex)

Same as theprecedingmethod, but withthe searchstarting atposition index inthe string. If thevalue of index is


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outside the legallimits for the

String object, -1 isreturned.

indexOf(String str)

Returns the indexposition of the 1st

occurrence of the

substring str inthe String objectfor which themethod is called.If the substring

str does notoccur, -1 isreturned.

indexOf(String str, intindex)

Same as theprecedingmethod, but withthe searchstarting at


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position index inthe string. If the

value of index isoutside the legallimits for theString object, -1 isreturned.

String string1 = The Ides ofMarch; Returns

FindCharacters.javaindexOfDemo.java

Example

VI (Exciting Concordance


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Extractin

String place = PalmSprings;

The variable lastWord will contthe string Springs, whcorresponds to the substring startat index position 5 in place throughthe end of the string. Copies the substring from the origito form a new String object.

Useful when a string has basically


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String segment = Enables us to extract a substrifrom a string by specifying tindex positions of the 1st characin the substring and one beyo

the last character of the substrias arguments to the method.

ExtractSubstrings.java

Example VII (Word for


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Tokenizing a

split Splits a string into tokens. Does this in a single step, returning the tokens from a string as an array

tring text = to be or not to be, that is the

uestion.;

Specifies a patternfor a delimiter. Anydelimiter that matchesthe pattern is assumed

to be a separator for a

An integer value that is a count of tmaximum no. of times the pattern can applied to find tokens and, therefore, affethe maximum no. of tokens that can

found. If 0, the pattern will be applied as matimes as possible, and any trailing emp

tring[ ] words = text.split([, .]);//

2nd argument

Example VIII (Using a Tokenizer)


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StringTokenizin

g.java

Modifying Versions of String

String newText = text.replace( , /);//Replaces each spain the string te

String sample = This isa string ;

Removes whitespace frothe beginning and end ostring (but not the interior

Creating Character Arrays from String Objec

tring text = To be or not to be;

har[ ] textArray = text.toCharArray();//

String text = To be ornot to be;char[ ] textArray = new

Copies characters from text at indpositions 9 to 11 inclusive, textArray[0] will be n, textArray[


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The indexposition ofthe 1st

characterto beextracted

The indexpositionfollowingthe lastcharacter tobeextracted

Thename ofthe arrayto holdthecharacte

Theindex ofthearrayelementto hold

Using the Collection-BasedforLoop with atring phrase = The quick brown fox

umped over the lazy dog.;nt vowels = 0;

or (char ch : phrase.toCharArray()) {ch = Character.toLowerCase(ch);if (ch == a || ch == e || ch == i || ch

== o || ch == u) {++vowels;

}

Cant use a String object direcas the source of values forcollection-based for loop.

getCharsDemo.javaTestGetChars.

java

Example IX (Using getChars())


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Obtaining the Characters in a String as an Array of

String text = To be or not to be;// Definea string

Creating String Objects from Character Arrahar[ ] textArray = {T, o, , b, e, , or, , n, o, t, , t, o, , b, e };tring text = String.copyValueOf(textArray)

ChangeCase.java.java

ExampleX (Changing


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The object text

references the string

String text =String.copyValueOf(textArray, 9,3);

Extracts 3 charactestarting wtextArray[9], so te

String(byteasciiChars[ ]);String(byteasciiChars[ ], int startInde

Creating String Objects from Byte Arrays

SubStringCons.java

Example XI (Using a byte


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Mutable strings Strings thatcan be changed

Immutable strings Stringsthat cant be changed

String objects cannot bechanged.

Mutable Strings

Strin Conversion & toStrin

public String

ExampleXII (Using

help.javahelp1.javatoStringDemo.java

StringBuffer and StringBuildobjects should be used whwe are transforming strin

frequently adding, deletinor replacing substrings instring. Operations will faster and easier usmutable objects. If we hamainly static strings that

occasionally need


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Use StringBuffer /StringBuilder

Thread- Not Thread-

CreatingStringBufferObjects

StringBuffer aString = new

tring phrase = Experience is what you gewhen youre expecting something else.;

tringBuffer myString = null;myString = new StringBuffer(Many a mickmakes a muckle);

Only the variable created that doesn

A StringBuffer variable can initialized with an exist

The Capacity of a StringBuffer


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A StringBuffer objectcontains a block of memory

called a buffer, which mayor may not contain a string,and if it does, the stringneed not occupy the entire

buffer. Thus, the length ofa string in a StringBufferobject can be differentfrom the length of thebuffer that the object

contains. The length of thebuffer is referred to as thecapacity of theStringBuffer object.


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When a StringBuffer object iscreated from an existing

string,capacity = string length

+ 16

The capacity of a StringBufferobject is not fixed though. Itgrows automatically as we add

Both the capacand the length ain units of Unico

characters, twice as ma


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to the string to accommodatea string of any length.

StringBuffer newString = new Object created wthe capacity to st50 characters. If the capacity vais omitted, the obj

int theCapacity = aString.lengt

aString.ensureCapa Used to change the default capacity If the current capacity of the aStriobject is less than 40, this will increase tcapacity of aString by allocating a nlarger buffer, but not necessarily with

capacity of 40. The capacity will be tlarger of either the value that we specify (

Changing the String Length for a StringBuffer

aString.setLen When the length for a StringBuffer objectincreased, characters are added to the exististring and the extra characters will conta\u0000.

More commonly used to decrease the lengt

aString.setLeng


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setLength() does notaffect the capacity of theobject unless the length isset to be greater than the

capacity. In this case thecapacity will be increasedto accommodate the newstring length to a valuethat is twice the original

capacity plus 2 if thelength we set is less thanthis value. If we specify alength that is greater than

twice the original capacityplus two, the new capacity


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will be the same as thelength we set.

The capacity will always beincreased automaticallywhenever necessary to

accommodate the longerstring.

//Assume, capacity of aString =66

//Assume, capacity of aString =66

Specifying a ve lengthrowsStringIndexOutOfBound

Adding to a StringBuffer Object

StringBuffer aString = new

StringBuffer(A stitch in time);

aString will conta

A stitch in ti


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append() returns a referenceto the extended StringBuffer

object, so we could also assignit to another StringBufferobject.

Multiple append() operationsin a single statement :-

StringBuffer bString =Now both aStriand bString poto the sam

tringBuffer proverb = new StringBuffer();/Capacity = 16

roverb.append(Many).append(

The . opera( membselection

operator) usto execute particularmethod for

Appending a

StringBuffer buf = newStringBuffer(Hard );String aString = Waxworks;


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Appending Basic

StringBuffer buf = newStringBuffer(The number is );long number = 999;

buf.append(12.34); // buf contains The

har[ ] text = { i, s, , e, x, a, c, t,, y};


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Data types that can be appended

to a StringBuffer objectboolean

int long String Object

char byte short float double

Finding the Position of a Substring

StringBuffer phrase = new StringBuffer(ontwo three four);

position =This statement starts the searchindex position 6 so the first characters (index values 0 to 5)

Replacing a Substring in the

tringBuffer phrase = new StringBuffer(onwo three four);tring substring = two;tring replacement = twenty;

nt position = phrase.lastIndexOf(substring)

Becausereplacemeis a strcontaining

morecharactersthansubstring, tlength of tstring inphrase will

increased, a


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Data types that can be used ininsert as a 2nd argumentboolean

int long String Object

char byte short float double

startindex inthe

Index position onebeyond the endindex of the

stringto

Inserting

/ Assume bufcontains the string Manyands make light work,

insert(int index, char[ ] str, intInserts a substring into tStringBuffer object starting position index. The substringthe String representation length characters from t


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Extracting Characters from a Mutable Strin

charAt()

Other Mutable String

buf.setCharAt(Sets the 4th character in the

tringBuffer phrase = newtringBuffer(When the boats come in);

phrase.deleteDeletes the substring the from

phrase, so it will then contain the stri

tringBuffer palindrome = newtringBuffer(so many dynamos);

Creating a StringObject from a StringBuffer


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toString() is used extensivelyby the compiler together with

append() to implement theconcatenation of Stringobjects.

Implementedby the compileras

tringBuffer proverb = newtringBuffer(Many hands make light work

tring saying = Many + hands +

tring saying = newtringBuffer().append(Many).append(

Example - 13


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UseStringBuffer.java

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Operations on Strings