Strings and a Helper Class

Some basics on Strings

· Strings can be ONE or more characters of text strung together

· “c” is a string

· “Mr. Lupoli stinks” is a string

· “123-213-1232” is a string

· “123123123” is a string

· Strings are immutable!!!

· If we make ANY changes we have to use the “=”

· A character data type cannot be a String

· To create a string

· notice when using Strings “” are used

· CHARACTERS use ‘ ’, you cannot use “”

String name = “Lupoli”;

String two = name; // equals is not just used for math

Index(ices)

[0]

[1]

[2]

[3]

[4]

[5]

[6]

[7]

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name

// notice a String starts at index 0!!

String Declaration and Initialization

· Sets aside an array of elements

· each element contains a String (single letter)

· Assigning values

· Must use “ “’s to set if literal

· variable = sc.next(); only reads up to the first white space.

· variable = sc.nextLine(); reads the whole line typed.

· don’t have to worry about declaring a SIZE that fits!! (automatically done!!)

· can use = to set a String

· can use + to concatenate

· No special treatment, just like any other variable

· MUST GIVE A DEFAULT VALUE!!! (“”)

String Declaration and Initialization

Gathering values into Strings Example 1

String firstName = “”, lastName = “”;

firstName = sc.next (); // input: Mr. Lupoli

lastName = sc.next ();

System.out.print(lastName + “, “ + firstName); // output: Lupoli, Mr.

firstName

lastName

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Gathering values into Strings Example 2

String firstName = “Kristen”;

String lastName = “Davis”;

System.out.print(lastName + “, “ + firstName); // output: Davis, Kristen

firstName

lastName

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Gathering values into Strings Example 3

String wholeName = “”;

wholeName = sc.nextLine(); // input: Mr. Lupoli

System.out.print(wholeName); // output: Lupoli, Mr.

wholename

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String as an Object

· a String is much more complicated than we know

· a String is an OBJECT (class)

· has helper function that give it more features

· treated as it’s OWN powerful identity

The OBJECT String

String as you know it

String as it really is

Code

Display/Result

String name = "Lupoli";

System.out.println(name.charAt(0));

System.out.println(name.length());

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What is a helper function?

· a pre-created code to help with mundane tasks

· gives the objects more features

· to use

· name of the variable “dot” helper function name

· many functions are used over and over again, why recreate the wheel!!

How to identify and read Helper functions

· API’s given by Java show all helper functions available

· Application Programming Interface

· think of it as a dictionary or directory

· API’s for Strings (Java 6)

· http://java.sun.com/javase/6/docs/api/java/lang/String.html

· General APIs

· http://java.sun.com/javase/6/docs/api/

API listing breakdown

Method Summary

char charAt(int index)           Returns the char value at the specified index.

what datatype the function gives back (returns) when called

name of function

what function needs in order to work (called a parameter)

Exploring what String Helper functions do

· use the code I give you below, and call the functions listed below

· see what displays

Use this code for exercise

public class helloWorld

{

public static void main(String[] args)

{

String name = "Lupoli";

System.out.println(name.charAt(0));

// Place all code for below here

}

} // may have to change the class name to match the file name

// complete the functions below on the code above to determine the output

function

code

Output

Datatype returned?

charAt

System.out.println(name.charAt(0));

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char

isEmpty()

toLowerCase()

toUpperCase()

indexOf(String str)

System.out.println(name.indexOf(“p”));

System.out.println(name.indexOf(“Z”));

DOUBLE QUOTES WILL BE OFF

Revisiting the ASCII Table

· alphabetical/numerical work just fine

· but mixing the two proves more interesting

· uses the ASCII table (covered in strings)

0 – 9 A – Z a – z

What value is A, a, Z and z respectfully?

What is the answer to below?

L u p o l i

76 117 112 111 108 105

Lupoli (<, >, ==) Luppold

Comparing Strings (more helper functions)

· normal comparison symbols do not work!!

· == , <=, >=, !=, >, <. etc…

· because String is a COMPLEX datatype

· compareTo

· compares two strings

· method returns a value

· == 0 (match)

· < 0 no match, S1 is alphabetically less than S2

· > 0 no match, S1 is alphabetically greater than S2

· equals (boolean)

· answer if an EXACT match

· compareToIgnoreCase/equalsIgnoreCase

· ignore case of strings, works the same way

// what is IgnoreCase??

Calling String helper function

· Same format each time

· Values returned can be placed in variables!!

(name of the string).(helper function)

Example String Helper Function Calls

int space = comment.indexOf(“ “);

String name = comment.substring(10);

String newLine = comment.replace(“Lupoli”, “Dork”);

Values compareTo( ) returns

String x = “cat”;

String y = “dog”;

x.compareTo(y);

returns

when

< 0

string1 alphabetically/ASCII before string2

cat dog

0

string1 alphabetically/ASCII INDENTICAL string2

cat cat

> 0

string1 alphabetically/ASCII” after string2

dog cat

compareTo in use

// compareTo example

String testOne = "Lupoli";

String testTwo = "Martino";

if(testOne.compareTo(testTwo) < 0)

{ System.out.println("testOne is LESS than testTwo"); }

else if(testOne.compareTo(testTwo) > 0)

{ System.out.println("testOne is GREATER than testTwo"); }

else // (testOne.compareTo(testTwo) == 0)

{ System.out.println("testOne is EQUAL to testTwo");}

if(testOne.compareTo("Lupoli") == 0)

{ System.out.print("Strings matched"); }

Values equals( ) returns

String x = “cat”;

String y = “dog”;

if( x.equals(y) ) // usually inside an IF statement

returns

when

0 (false)

string1 alphabetically/ASCII NOT IDENTICAL string2

1 (true)

string1 alphabetically/ASCII IDENTICAL string2

equal

// equal example

testOne = "Lupoli";

testTwo = "Martino";

if(testOne.equals(testTwo))

{ System.out.println("testOne is LESS than testTwo"); }

else // (testOne.equals(testTwo) == 0)

{ System.out.println("testOne is EQUAL than testTwo"); }

if(testOne.equals("Lupoli"))

{ System.out.println("Strings matched"); }

String comparing exercise

String 1 (x)

String 2 (y)

comparison

Answer

cat

dog

x.equals(y)

false

Lupoli

Luppold

x.compareTo(y)

Zach

Emily

x.compareTo(y)

Eric

Eric

x.compareTo(y)

Mandy

MANDY

x.equals(y)

Mandy

MANDY

x.equalsIgnoreCase(y)

So… Strings are immutable, so what??

· Remember Strings are immutable

Non-immutable strings example

public class Example {

public static void main(String[] args) {

String answer = "Lupoli";

// trying to add something WITHOUT resetting the string

answer.concat(" is awesome");

System.out.println("And we now have: " + answer);

// trying to add something WITH resetting the string

answer = answer + " stinks";

System.out.println("And we now have: " + answer);

}

}

And we now have: Lupoli

And we now have: Lupoli stinks

· We now have StringBuilder

· Strings that are mutable

· http://docs.oracle.com/javase/7/docs/api/java/lang/StringBuilder.html

Editing elements in a String array

· HAVE TO DELCARE THE STRING FIRST!!!

· individual characters inside a String array can be accessed.

Accessing a value inside an String

String fname = “John”;

System.out.print(“Character at index 2 is “ + fname[2] + “\n”); // displays ‘h’

[0]

[1]

[2]

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[4]

[5]

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[7]

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\0

Editing a value inside a String

String fname = "John";

fname = fname.replace('h', 'X'); // editing element number 2, NOTICE NO CHAR!!

System.out.print("Name: " + fname + "\n"); // displays “JoXn”

[0]

[1]

[2]

[3]

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\0

FYI another way:

result = 't' + result.substring(1,result.length())

Finding a “null” or “” in a String/array of Strings

· you might find that an array element does not contain viable data

· to find, use the “.equals()” string command

· commonly mistaken what to do

Common search errors

String

String in an Array

if(answers[i] != "") { length++; }

if(answers[i] != " ") { length++; } if(answers[i] != null) { length++; }

if(answers[i] != "null") { length++; }

Correct null search code

String

String in an Array

String type = “”;

if(answers.equals(""))

if(!answers[i].equals("") ) { length++; }

Concatenation

· adds to END of existing String

· the string will increase in size automatically

· syntax

· final = original + attachment;

· final = original.concat(attachment);

· concat will ONLY work with Strings (not ints)

Code

Visually

String string1 = “Goodbye”;

String string2 = “, Cruel ”;

string1 = string1 + string2;

string1 = string1 + “World!”; // literal string

string1

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string1

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string1

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Determine what “answer” will look like after the code below WITHOUT A COMPILER!!! Draw it out!!!

1. String string1 = “Goodbye”; // drawn below

2. String string2 = “, Cruel ”;

3. String answer = “”;

4. answer = answer + string1;

5. answer += string2; // hmmm, think about it!!

6. string1 = “Lupoli”;

7. answer = answer + string1;

8. System.out.println(answer); // put answer below (if not already!)

string1

string2

answer

Search Methods

contains methods

returns

method

 boolean

contains(CharSequence s) Returns true if and only if this string contains the specified sequence of char values.

String line = "Mr. Lupoli is a programming professor";

if(line.contains("Lupoli") || line.contains("LUPOLI"))

{ System.out.println("Yeah, he's in there"); }

else

{ System.out.println("Nope, not in there"); }

String variable = "Munson";

if(line.contains(variable))

{ System.out.println("Yeah, he's in there"); }

lastIndexOf method

 int

lastIndexOf(int ch)           Returns the index within this string of the last occurrence of the specified character.

 int

lastIndexOf(int ch, int fromIndex)           Returns the index within this string of the last occurrence of the specified character, searching backward starting at the specified index.

 int

indexOf(String str)           Returns the index within this string of the first occurrence of the specified substring.

String line = "Mr. Lupoli is a programmer professor";

1. What direction will the search start?

2. What datatypes will these functions below return??

3. What are these functions returning in general?

4. Determine what each display will produce System.out.println(line.lastIndexOf("pro"));

System.out.println(line.lastIndexOf('o'));

System.out.println(line.lastIndexOf('o', 20));

substring methods

 String

substring(int beginIndex)           Returns a new string that is a substring of this string.

 String

substring(int beginIndex, int endIndex)           Returns a new string that is a substring of this string.

String line = "Mr. Lupoli is a programming professor";

// Determine what each display will produce

String subString1 = line.substring(4);

System.out.println(subString1);

String subString2 = line.substring(4, 9);

System.out.println(subString2);

Converting a number to a Stringint value = 27;

String greeting = “Hello There”;

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String complete = greeting + value; // just the same as concatenation of 2 Strings!!

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Converting Strings to Numbers - FYI

There will be many times were the input interface will treat whatever the user types in as a String, (JOptionPane), we can then transform that input into the format intended.

String x;

int real_number;

realnumber = Integer.parseInt(x); // now “realnumber” is actually an INT value 23

Type Name

Method for conversion

byte

Byte.parseByte(String_to_convert)

short

Short.parseShort(String_to_convert)

int

Integer.parseInt(String_to_convert)

long

Long.parseLong(String_to_convert)

float

Float.parseFloat(String_to_convert)

double

Double.parseDouble(String_to_convert)

// x = JOptionPane.showDialog(“Enter a whole number:”); // “x” is a STRING 23

Helper Method - Char at (charAt)

· returns a CHAR value from a specific AND single location in the string

· great for grabbing the FIRST letter of a first name for a username

· usually in if statements and for loops

· great for counting spaces

charAt() function

Returns

Syntax

char

charAt(int index)           Returns the char value at the specified index.

name

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int frequency = 0;

for(int i = 0; i < name.length(); i++)

{

if(name.charAt(i) == ' ') { frequency++; }

} // counts # of spaces in the name

String Tokenizer

· import java.util.StringTokenizer;

· breaks input line into a sequence of Strings (words) separated by spaces

· CANNOT TOKENIZE INDIVIDUAL LETTERS (use .charAt( ))

· this String below was read in using sc.readLine( );

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tokens

(separated by spaces)

String inputline = sc.nextLine( );

StringTokenizer tokenizer = new StringTokenizer(inputline);

Other tokenize functions

tokenizer.hasMoreTokens( );

· determines if more “tokens” in the String

· used usually in a conditional loop

String word = tokenizer.nextToken( );

· grabs next token, assigns to “word”

· records last place it grabbed a word

int count = tokenizer.countTokens( );

returns the number of tokens remaining to be returned by NEXTTOKEN()

Introduction to the While Loop

· Condition is tested BEFORE body of the loop

· used when NOT sure when it may end

· need a priming read to test condition before it will loop

· priming read, ask for a value, tests the answer with the loop condition

While Loop Structure

Flowchart Example

1

Yes

Inside loop body

5

4

2

3

No

Continue outside of loop body

While Loop

While loop Example

// import Scanner!!

Scanner sc = new Scanner(System.in);

public static void main(String args[]){ int getValue, setTotal;

/* Give directions to user */ System.out.print( “This program adds a list of numbers.\n”); System.out.print( “Signal end of list with a 0.\n”);

setTotal = 0; /* Initialize setTotal */

/* Get integers from the user until a 0 is entered */

// Get the first integer from the user

// This is known as a "priming read" */

System.out.print( “Enter an integer, 0 to end : \n”);

getValue = sc.nextInt();

// Continue to get integers from the user

// until a 0 is entered, accumulating into setTotal

while (getValue != 0)

{

setTotal = setTotal + getValue; // running setTotal

System.out.print( “Enter an integer, 0 to end : \n”);

getValue = sc.nextInt();

}

/* Print the total */ System.out.print( “The total is “ + setTotal + “\n”);}

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Scanner sc = new Scanner(System.in);

String inputline = sc.nextLine( ); // user inputted line above

StringTokenizer tokenizer = new StringTokenizer(inputline);

Use the loop to grab each token from the string and display each token. Some of the answer is given below. Loop at the Java API for StringTokenizer (or Tokenizer functions above) to see if there is a way to determine IF there are no tokens left!!

while( )

{

System.out.println( );

}

Array of Strings

String [] nameOfDay = { // Array of 7 string

"Sunday",

"Monday",

"Tuesday",

"Wednesday",

"Thursday",

"Friday",

"Saturday"

};

Sunday Tuesday Thursday Saturday

0 1 2 3 4 5 6

Monday Wednesday Friday

System.out.println(nameOfDay[5]); // displays “Friday”

Breaking down a String

· you can look at individual chars inside a string

· use the char functions to determine what is inside that string

· isLetter

· isDigit

· isWhitespace

· isLowerCase

· isUpperCase

String line = “Goodbye, Cruel World”;

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√

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√

√

√

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√

Total = 17

Is Upper Letter example

int count = 0;

for(int i = 0; i < line.length(); i++) // counts # of letters in the string

{

if(Character.isUpperCase(line.charAt(i))){ count++; }

}

System.out.println(count);

isDigit example

int count = 0;

for(int i = 0; i < line.length(); i++) // counts # of numbers in the string

{

if(Character.isDigit(line.charAt(i))){ count++; }

}

System.out.println(count);

1. Assign helper functions to teams

2. Have them look up how to use the functions (find examples on google)

a. simple examples!! You will find crazy ones

3. Test example by coding it in Eclipse (copy paste, adjust slightly)

4. Create a new example using the function degrading Lupoli

String start = “Lupoli needs a vacation”;

String answer = start.replace(‘i’, ‘ ‘);

System.out.println(answer);

5. Draw what the function is doing in an animation/cartoon

a. make sure to explain, BUT NOT IN SENTENCES!!

b. use markers to draw

c. use the entire paper, make it as big as you can!

i. yes, we can try, try again

d. place name in lower right corner (small)

e. please be neat

f. be creative!!!

g. check with Mr. Hughes or Mr. Lupoli when completed

6. Will combine into ONE document so all can use!!!

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