Strings

1
Strings

• Instructor Mainak Chaudhuri
• mainakc_at_cse.iitk.ac.in

2
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

3
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

4
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)

5
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

6
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

7
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

8
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

9
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

10
Converting string to integer

• class StringToInt
• public static void main (String arg)
• // Assume arg0 is the input string
• int result 0, pos
• int len arg0.length()
• char c
• for (pos 0 pos
• c arg0.charAt(len-pos-1)
• if ((c 0) (c
• result ((c-0)Math.pow(10,
  pos))
• // continued in next slide

11
Converting string to integer

• else if ((c-) (poslen-1))
• result -result
• else
• System.out.println(Invalid input
  arg0)
• break
• // end for
• if (poslen)
• System.out.println(Integer value
  result)

12
Reversing a string

• class StringReverse
• public static void main (String arg)
• // Assume that the input is arg0
• String reversed
• int pos
• for (posarg0.length()-1 pos 0
  pos--)
• reversed arg0.charAt(pos)
• System.out.println (Original arg0
  , Reversed reversed)

13
Sorting a list of names

• class NaiveDictionarySort
• public static void main (String arg)
• // Assume that the names are in arg
• int n arg.length // list size
• String sortedList new Stringn
• boolean indexArray new booleann
• int k, j, runningIndex0, minIndex
• for (k0 k
• indexArrayk false
• // continued on next slide

14
Sorting a list of names

• while (runningIndex
• for (k0 k
• if (!indexArrayk) break
• sortedListrunningIndex argk
• minIndex k
• for (jk1 j
• if (indexArrayj) continue
• if (sortedListrunningIndex.compare
  To(argj) 0)
• sortedListrunningIndex
  argj
• minIndex j
• // continued on next slide

15
Sorting a list of names

• indexArrayminIndex true
• runningIndex
• System.out.println (Sorted list)
• for (k0 k
• System.out.println (sortedListk)

16
Announcement

• Batches B9 and B10 will go for lab08 this Sunday
  1000-1300
• No class this Sunday
• This is not a Wednesday compensation