Strings

1
Strings

• Can view as array of chartacters
• Implemented as a class with its own methods
• Simplest operation on strings is catenating two
  strings
• String x Good
• String y Morning!
• String z x y
• String w x y // also works
• Possible to concatenate strings to variables of
  other types e.g., int, float, etc.
• Internally converted to string

2
Methods of string class

• Determining the length of a string
• String x abc
• int lengthOfx x.length()
• Determining the character at a position
• String x abc
• char cAt2 x.charAt(2)
• char first x.charAt(0)
• char last x.charAt(x.length()-1)
• Case conversion
• String x Mainak
• String y x.toUpperCase() // y is MAINAK
• String z x.toLowerCase() // z is mainak

3
More on concatenation

• Concatenating strings is different from
  concatenating characters
• String x a
• String y b
• String z x y // z is ab
• char x1 a
• char y1 b
• char z1 x1 y1 // z is not ab
• For concatenating two strings you can use the
  concat method also
• String z to.concat(get).concat(her)

4
Extracting substrings

• Can extract the substring starting at a position
• String x together
• String y x.substring(2) // y is gether
• String z x.substring(3) // z is ether
• String w x.substring(0) // same as x
• String u x.substring(x.length()-1) // r
• String v x.substring(x.length()) // blank
• Can extract substring between two positions
• String y x.substring(0, 5) // y is toget
• String z x.substring(5, x.length()) // her
• String w x.substring(5, 6) // w is h
• String u x.substring(5, 5) // u is

5
Searching in a string

• Finding the first occurrence of a character or a
  substring within a string
• String x abracadabra
• int k x.indexOf(a) // k is 0
• int p x.indexOf(a, 1) // p is 3 search
• // begins from pos 1
• int t x.indexOf(e) // t is -1
• int q x.indexOf(ra) // q is 2
• int s x.indexOf(ra, 3) // s is 9
• Possible to find the last occurrence also
• int p x.lastIndexOf(r) // p is 9

6
Comparison of strings

• Compares strings in dictionary order (also known
  as lexicographical order)
• Returns zero if strings are equal
• String x abc
• String y abcd
• String z ab
• String w abd
• int p x.compareTo(y) // p is negative
• int q x.compareTo(x) // q is zero
• int r x.compareTo(z) // r is positive
• int s y.compareTo(w) // s is negative
• This comparison is case sensitive
• Use compareToIgnoreCase otherwise

7
Some more useful methods

• Removing leading and trailing whitespaces
• String x abc
• String y x.trim() // y is abc
• Test for prefix
• String x Mainak
• boolean y x.startsWith(Main) // y is true
• boolean z x.startsWith(nak, 3) // z is true
• Test for suffix
• String x Canada
• boolean y x.endsWith(ada) // y is true

8
Some more useful methods

• Substitute all occurrences of a character with
  another character
• String x deer
• String y x.replace(e, o) // y is door
• String z x.replace(a, o) // z is deer
• Partial string match
• String x abracadabra
• boolean y x.regionMatches(true, 2, bracket,
  1, 3) // y is true
• The first argument should be set to true if the
  match is intended to be case ignorant

9
regionMatches

• boolean regionMatches(int toffset, String other,
  int ooffset, int len)
• Tests whether the specified region of this string
  matches the specified region of the String
  argument.
• Region is of length len and begins at the index
  toffset for this string and ooffset for the other
  string.

10
regionMatches

• boolean regionMatches(boolean ignoreCase, int
  toffset, String other, int ooffset, int len)
• Tests whether the specified region of this string
  matches the specified region of the String
  argument. Region is of length len and begins at
  the index toffset for this string and ooffset for
  the other string.
• The boolean argument indicates whether case
  should be ignored if true, case is ignored when
  comparing characters.

11
RegionMatchesDemo

• public class RegionMatchesDemo
• public static void main(String args)
• String searchMe "Green Eggs and Ham"
• String findMe "Eggs"
• int searchMeLength searchMe.length()
• int findMeLength findMe.length()
• boolean foundIt false
• for (int i 0 i lt (searchMeLength -
  findMeLength) i)
• if (searchMe.regionMatches(i, findMe, 0,
  findMeLength))
• foundIt true
• System.out.println(searchMe.substring(i,
  i findMeLength))
• break
• if (!foundIt) System.out.println("No match
  found.")

12

• The program steps through the string referred to
  by searchMe one character at a time. For each
  character, the program calls the regionMatches
  method to determine whether the substring
  beginning with the current character matches the
  string the program is looking for.
• The output from this program is Eggs.