Characters Strings

7/27/2019 Characters Strings

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Characters, Strings and the String

Buffer

Jim Burns


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Identifying problems that can occur when

you manipulate string data

String is not a simple data type like int, float,or double

String creates an instance of a class, the class

String As such it contains a reference or an address

and not the actual string

So you cannot do equality comparisons of twodifferent instances of String, because you aresimply testing if the addresses are the same


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An example of incorrect code

import javax.swing.JOptionPane;

public class TryToCompareStrings{

public static void main(String[] args)

{

String aName = "Carmen";

String anotherName;anotherName = JOptionPane.showInputDialog(null,

"Enter your name");

if(aName == anotherName)

JOptionPane.showMessageDialog(null, aName +

" equals " + anotherName);

else


" does not equal " + anotherName);

System.exit(0);

}

}


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Correct Code import javax.swing.JOptionPane;

public class CompareStrings

{ public static void main(String[] args)

{

String aName = "Carmen";

String anotherName;

anotherName = JOptionPane.showInputDialog(null, "Enter your name");

if(aName.equals(anotherName))


" equals " + anotherName);

else JOptionPane.showMessageDialog(null, aName +

" does not equal " + anotherName);

System.exit(0);

}

}


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Three classes for working with strings

Charactera class whose instances can hold a single

character valueprovides methods that can

manipulate or inspect single-character data

Stringa class for working with fixed-string datathat is unchanging data composed of multiple

characters, strings that are immutable

StringBuffera class for storing and manipulating

changeable data composed of mulltiple characters


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Manipulating Characters

We know the char data type can hold anysingle character

Character class provides the following

methods isUpperCase(), toUpperCase(), isLowerCase(),

toLowerCase(), isDigit(), isLetter(),isLetterOrDigit(), isWhitespace()

Methods that begin with is perform testsdelivering true or false values

Methods that begin with to performconversions


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Declaring a String Object

We know that characters enclosed within doublequotation marks are literal strings

Weve learned to print these strings using println()and showMessageDialog()

An literal string is an unnamed object, or anonymousobject, of the String class

A String variable is simply a named object of thesame class.

The class String is defined in java.lang.String, which isautomatically imported into every program you write


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With or without a String Constructor

With the constructor

String aGreeting = new String(Hello);

Without the constructor

String aGreeting = Hello;

Unlike other classes, you can create a String objectwithout using the keyword new or explicitly calling

the class constructor


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Comparing String Values

Consider the following two statements:

String aGreeting = hello;

aGreeting = Bonjour;

These statements are syntactically correct. Whathappens is that the address contained in aGreeting ischanged to point to Bonjour rather than hello,both of which are contained at different locations inmemory. Eventually, the garbage collector discardsthe hello characters.


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Comparing String Values

The String class provides methods for

comparing strings

In the example above the == sign is comparing

memory addresses, not the actual strings.

The String class equals() method evaluates the

contents of two String objects to determine if

they are equivalent.

I j i JO i P


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Import javax.swing.JOptionPane;

Public class CompareStrings

{

public static void main(String[] args){

String aName = Carmen, anotherName;

anotherName = JOptionPane. showInputDialog(null,

Enter your name);if(aName.equals(anotherName))

JOptionPane.showMessageDialog(null, aName + equals + anotherName);

elseJOptionPane.showMessageDialog(null, aName + does

not equal + anotherName));

System.exit(0);

}


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The equals() method

From the code above, we can see that the

equals() method returns a Boolean value of

true or false


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equalsIgnoreCase() Method

Similar to the equals() method

Ignores case

String aName = Roger;If(aName.equalsIgnoreCase(roGER))

evaluates to true


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compareTo() method

Returns an integer that is the numeric difference

between the first two non-matching

characters


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Using other String Methods

toUpperCase() and toLowerCase() convert any

String to its uppercase and lowercase

equivalent

Length() returns the length of a String

import javax swing *;


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import javax.swing. ;

public class BusinessLetter

{


{

String name;

String firstName = "";

String familyName = "";

int x;char c;

name = JOptionPane.showInputDialog(null,

"Please enter customer's first and last name");

x = 0;

while(x < name.length())

{

if(name.charAt(x) == ' ')

{

firstName = name.substring(0, x);familyName = name.substring(x + 1, name.length());

x = name.length();

}

++x;

}

JOptionPane.showMessageDialog(null,

"Dear " + firstName +

",\nI am so glad we are on a first name basis" +

"\nbecause I would like the opportunity to" +"\ntalk to you about an affordable insurance" +

"\nprotection plan for the entire " + familyName +

"\nfamily. Call A-One Family Insurance today" +

"\nat 1-800-555-9287.");

System.exit(0);

}

}

0


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x = 0;

while(x < name.length())

{

if(name.charAt(x) == ' ')

{

firstName = name.substring(0, x);

familyName = name.substring(x + 1,name.length());

x = name.length();

}

++x;

}


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Concatenation

You know you can concatenate strings to

strings as in System.out.println(firstName +

+ lastName);


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Concatenationnumbers to strings by

using +

The following is permissible:

Int myAge = 25;

String aString = My age is + myAge; Another example would be

String anotherString;

float someFloat = 12.34f;anotherString = + someFloat;


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Concatenation by using the toString()

method

String theString;

Int someInt = 10;

theString = Integer.toString(someInt);

String aString;

double someDouble = 8.25;aString = Double.toString(someDouble);


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Converting Strings to Numbers

Use a wrapper like the Integer class which is a

part of java.lang

A wrapper is a class that is wrapped around

a simpler element

Int anInt = Integer.parseInt(649) stores the

value 649 in the variable anInt

public class TestCharacter


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p

{


{

char aChar = 'C';

System.out.println("The character is " + aChar);

if(Character.isUpperCase(aChar))

System.out.println(aChar + " is uppercase");else

System.out.println(aChar + " is not uppercase");

if(Character.isLowerCase(aChar))

System.out.println(aChar + " is lowercase");

else

System.out.println(aChar + " is not lowercase");

aChar = Character.toLowerCase(aChar);

System.out.println("After toLowerCase(), aChar is " + aChar);

aChar = Character.toUpperCase(aChar);

System.out.println("After toUpperCase(), aChar is " + aChar);

if(Character.isLetterOrDigit(aChar))

System.out.println(aChar + " is a letter or digit");

else

System.out.println(aChar + " is neither a letter nor a digit");

if(Character.isWhitespace(aChar))System.out.println(aChar + " is whitespace");

else

System.out.println(aChar + " is not whitespace");

}

}

//see next slide

T Ch A


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Test Character Apppublic class TestCharacter

{

public static void main(String[] args){

char aChar = 'C';

System.out.println("The character is " + aChar);

if(Character.isUpperCase(aChar))System.out.println(aChar + " is uppercase");

else

System.out.println(aChar + " is not uppercase");

if(Character.isLowerCase(aChar))

System.out.println(aChar + " is lowercase");

else

System out println(aChar + " is not lowercase");


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System.out.println(aChar + is not lowercase );

aChar = Character.toLowerCase(aChar);

System.out.println("After toLowerCase(), aChar is " + aChar);

aChar = Character.toUpperCase(aChar);

System.out.println("After toUpperCase(), aChar is " + aChar);if(Character.isLetterOrDigit(aChar))

System.out.println(aChar + " is a letter or digit");

else

System.out.println(aChar + " is neither a letter nor a digit");

if(Character.isWhitespace(aChar))

System.out.println(aChar + " is whitespace");

else

System.out.println(aChar + " is not whitespace");

}}


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Learning about the StringBuffer Class

Some strings are not constants, not immutable

String someChars = Goodbye;

someChars = Goodbye Everybody;

someChars = Goodbye + Everybody; You cannot change the string Goodbye

To overcome these limitations, you can use theStringBuffer class

The StringBuffer class was invented to accommodatestrings that are not immutable (constants)


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The StringBuffer Class

Uses a buffer that is much larger than any one

string; actual size of the buffer is the capacity

Provides methods that can change individual

characters within a string

Must initialize StringBuffer objects as follows:

StringBuffer eventString = new StringBuffer(Hello

there);

Cannot use StringBuffer eventString = Hello

there;

M h d i h S i B ff Cl


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Methods in the StringBuffer Class setLength() will change the length of a String in

a StringBuffer object capacity() will find the capacity of an object

Has four constructors:

public StringBuffer() constructs a StringBuffer withno characters and a default size of 16 characters

public StringBuffer(int Capacity) creates a

StringBuffer with no characters and a capacity

defined by the parameter

public StringBuffer(String s) contains the same

characters as those stored in the String object s


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Still more methods in the StringBuffer

Class

Append() lets you add characters to the end of

a StringBuffer object

Insert() lets you add characters at a specific

location within a StringBuffer object

StringBuffer someBuffer = new StringBuffer(Happy

Birthday);

someBuffer.insert(6,30th);

Produces Happy 30thBirthday


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Still more methods in StringBuffer

setCharAt() method allows you to change a single

character at a specified location

someBuffer.setCharAt(6,4);

Changes someBuffer to Happy 40th

Birthday Can use charAt() method will return the character at

an offset number of positions from the first character

StringBuffer text = new StringBuffer(Java Programming);

Then text.charAt(5) returns the character P.

package Strings;import javax swing *;


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import javax.swing. ;

publicclass RepairName {

/**

* @param args

*/

publicstaticvoid main(String[] args)

{

String name, saveOriginalName;

int stringLength;int i;

char c;

name = JOptionPane.showInputDialog(null, "Please enter your first and last name");

saveOriginalName = name;

stringLength = name.length();

for (i=0; i < stringLength; i++)

{

c = name.charAt(i);

if(i==0)

{

c = Character.toUpperCase(c);name = c + name.substring(1, stringLength);

}

else

if(name.charAt(i) == ' ')

{

++i;

c = name.charAt(i);

c = Character.toUpperCase(c);

name = name.substring(0, i) + c + name.substring(i + 1, stringLength);

}}

JOptionPane.showMessageDialog(null, "Original name was " + saveOriginalName + "\nRepaired name is " + name);

System.exit(0);

}

// TODO Auto-generated method stub

}

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Characters Strings