Stringing Along in Java

1
Stringing Along in Java
A Java Class in Action

• CS 102-02
• Lecture 6-1

2
Today in a Nutshell

• Characters and strings
• Methods on strings
• Substrings
• Buffered strings

3
"Whats a String?"

• A string is a bunch of characters treated as a
  single unit
• Characters are the building blocks
• ASCII is a 7-bit encoding (variations are 8-bit)
• Unicode is a 16-bit encoding

4
Global Strings

• Globalization makes characters complicated
• Locales
• Locale object represents a specific geographical,
  political, or cultural region
• Locale-sensitive operations use a Locale object
  to tailor information for the user
• Example Displaying a number

5
Strings in Java

• String is a class in Java
• Strings are constant (values cannot be changed
  after they are created)
• Set of characters "Lisa Simpson" is an anonymous
  string (aka, string constant or literal string)
• "A" is a string, 'A' is a character

6
Here, There and Everywhere

• Strings are very common in programming
• Text is everywhere
• Strings are good for short pieces of text
• String manipulation
• Find the length of strings
• Extract characters
• Compare strings

7
How Long?

• Use length() to find out how long a string is
• String test
• test new String("The quick, brown")
• System.out.println("Length of test is "
• test.length())
• Works on anonymous strings too
• System.out.println("'Lisa Simpson' is "
• "Lisa Simpson".length()
• " characters long.")

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Strings are Character Sequences

• Grab individual characters with charAt()
• public char charAt(int index)
• A quick example
• for (int nextChar 0 nextChar lt test.length()
  nextChar)
• g.drawString(test.charAt(nextChar), xPos,
• yPos(15nextChar))

9
More for Your Money

• Get more than one character at atime with
  getChars()
• public void getChars(int srcBegin, int srcEnd,
  char dst, int dstBegin)
• Copies characters from this string into the
  destination character array.
• First character is at index srcBegin
• Last character to be copied is at index srcEnd-1
• Subarray of dst starting at index dstBegin and
  ending at index
• dstbegin (srcEnd-srcBegin) - 1

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Comparing Strings

• What do the concepts , lt and gt mean for
  strings?
• Compare initial characters in a string
• Different than numbers
• Upper and lower case
• Java uses lexicographic ordering

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Comparing Strings

• Are two strings equal (including upper and lower
  case)?
• public boolean equals(Object anObject)
• "ABC".equals("ABC") is true
• "ABC".equals("abc") is false
• If you want to ignore case, use
• public boolean equalsIgnoreCase(String
  anotherString)

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, lt or gt ?

• Comparing two strings
• public int compareTo(String anotherString)
• 0 if the argument string is equal to this string
• Less than 0 if this string is lexicographically
  less than the string argument
• Greater than 0 if this string is
  lexicographically greater than the string argument

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Comparing Substrings

• Use regionMatches to heck for equality within
  two strings
• public boolean regionMatches(int toffset, String
  other, int ooffset, int len)
• Example
• "A quick, brown fox".regionMatches(7, "An old,
  brown banana", 6, 7)

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Comparing Regions
Offset 7

• "A quick, brown fox"
• 0123456789
• "An old, brown banana"

Length 7
Offset 6
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Finding the Substring of Your Dreams

• Find characters (and sequences of characters)
  within strings
• Looking for characters?
• indexOf(int)
• indexOf(int, int)
• indexOf(String)
• indexOf(String, int)

lastIndexOf(int) lastIndexOf(int, int)
lastIndexOf(String) lastIndexOf(String, int)
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Getting the Index

• Examples
• "abcdefabc".indexOf((int) 'c') is 2
• "abcdefabc".indexOf("bc") is 1
• "abcdefabc".lastIndexOf("bc") is 7
• "abcdefabc".indexOf((int) 'a', 5) is 6

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Substrings

• A substring is a string within a string
• Two substring methods
• public String substring(int beginIndex) Starts
  with index and grabs the remainder of the string
• public String substring(int beginIndex, int
  endIndex)
• Includes character at beginIndex, but not the
  character at endIndex

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The String's the Thing

• Strings are an easily understandable format
• Need to convert a variable to something readable?
  Try valueOf()!
• boolean char char char, int, int double
• float int long Object
• For Object, valueOf() returns the same as
  obj.toString()
• A string that "textually represents" this object

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Replacing String Characters

• Replace one character with another in a new
  string
• replace(char oldChar, char newChar)
• Example
• String name
• "Babe, toe soeep-oerding pig"
• name.replace('o', 'h')

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Case Conversion

• Make a copy of a string, all in one case
• Handy for enforcing consistency always switch
  strings to upper case or lower case
• public String toLowerCase(Locale locale)
• public String toLowerCase()
• public String toUpperCase(Locale locale)
• public String toUpperCase()

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Trimming Away Excess String

• Throw away leading and trailing whitespace
• Makes matching more reliable
• public String trim()
• All characters that have codes less than or equal
  to '\u0020' (the space character) are considered
  to be white space

22
Buffer the String Slayer

• Strings are immutable objects
• Methods that seem to modify a string actually
  create a new string object
• Buffered strings can be modified
• Buffered strings have two "lengths"
• Current length of the string
• Buffer length (capacity)

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More on String Buffers

• Strings buffers are great when you need to do
  extensive string manipulation
• Handy for communications between programs
• Two programs can communicate with one another
  (for example, email)
• Store incoming and outgoing messages in buffers