Split a String into a Number of Substrings in Java

17 Feb, 2022
Given a String, the task it to split the String into a number of substrings.
A String in java can be of 0 or more characters. 
Examples :
(a) "" is a String in java with 0 character
(b) "d" is a String in java with 1 character
(c) "This is a sentence." is a string with 19 characters.

Substring: A String that is a part of another string is called substring of the other string.
Example 1: Let us consider the string bat. The possible substrings are:
(1) "b"
(2) "ba"
(3) "bat", every string is a substring of itself
(4) "a"
(5) "at"
(6) "t"
(7) ""  , "" is a substring of every string

Example 2: Let us consider the string The Cat. The possible substrings are: 
(1) "T"
(2) "Th"
(3) "The"
(4) "The "
(5) "The C"
(6) "The Ca"
(7) "The Cat", every string is a substring of itself
(8) "h"
(9) "he"
(10) "he "
(11) "he C"
(12) "he Ca"
(13) "he Cat"
(14) "e"
(15) "e "
(16) "e C"
(17) "e Ca"
(18) "e Cat"
(19) " "
(20) " C"
(21) " Ca"
(22) " Cat"
(23) "C"
(24) "Ca"
(25) "Cat"
(26) "a"
(27) "at"
(28) "t"
(29) ""  , "" is a substring of every string


Note: Total number of substrings of a string of length N is (N * (N + 1)) / 2. This is after excluding the empty string “” because it is a substring of all strings.
Approach:
Let us consider a string which has n characters:
1. For each character at index i (0 to n-1):
        find substrings of length 1, 2, ..., n-i
        

Example: Let our string be cat, here n = 3 (the length of string)
here, 
    index of 'c' is 0
    index of 'a' is 1
    index of 't' is 2
    
Loop from i = 0 to 2: (since n-1 = 2)

When i = 0:
    Substring of length 1 : "c"   
    Substring of length 2 : "ca" 
    Substring of length 3 : "cat" , (substring of length n-i or 3-0 = 3)
    
When i = 1:
    Substring of length 1 : "a"
    Substring of length 2 : "at" , (substring of length n-i or 3-1 = 2)
    
When i = 2:
    Substring of length 1 : "t" , (substring of length n-i or 3-2 = 1)

Example: 
Java
// Java Program to split a string into all possible// substrings excluding the string with 0 characters i.e. ""  import java.io.*;import java.util.ArrayList;  class SubstringsOfAString {      // function to split a string into all its substrings    // and return the list as an object of ArrayList    public static ArrayList<String>    splitSubstrings(String s)    {          // variables to traverse through the        // string        int i, j;          // to store the length of the        // string        int stringLength = s.length();          // List object to store the list of        // all substrings of the string s        ArrayList<String> subStringList            = new ArrayList<String>();          // first for loop        for (i = 0; i < stringLength; i++) {              for (j = i + 1; j <= stringLength; j++) {                  subStringList.add(s.substring(i, j));            }          } // end of first for loop          // returning the list (object        // of ArrayList) of substrings        // of string s        return subStringList;    }      public static void main(String[] args)    {          // here "The Cat" is our input string        String stringInput = new String("The Cat");          ArrayList<String> subStringList            = SubstringsOfAString.splitSubstrings(                stringInput);          System.out.println(            "\nSubstring list printed as an ArrayList : ");        System.out.println(subStringList);          System.out.println(            "\n\nAll substrings printed 1 per line : ");        int count = 1;          // each substring would be printed        // within double quotes        for (String it : subStringList) {            System.out.println("(" + count + ") \"" + it                               + "\"");            count++;        }    }}
Substring list printed as an ArrayList : 
[T, Th, The, The , The C, The Ca, The Cat, h, he, he , he C, he Ca, he Cat, e, e , e C, e Ca, e Cat,  ,  C,  Ca,  Cat, C, Ca, Cat, a, at, t]


All substrings printed 1 per line : 
(1) "T"
(2) "Th"
(3) "The"
(4) "The "
(5) "The C"
(6) "The Ca"
(7) "The Cat"
(8) "h"
(9) "he"
(10) "he "
(11) "he C"
(12) "he Ca"
(13) "he Cat"
(14) "e"
(15) "e "
(16) "e C"
(17) "e Ca"
(18) "e Cat"
(19) " "
(20) " C"
(21) " Ca"
(22) " Cat"
(23) "C"
(24) "Ca"
(25) "Cat"
(26) "a"
(27) "at"
(28) "t"


Time Complexity: O(n2) where n is the length of  a string  
Output 1: When string Input = bat
Substring list printed as an ArrayList : 
[b, ba, bat, a, at, t]


All substrings printed 1 per line : 
(1) "b"
(2) "ba"
(3) "bat"
(4) "a"
(5) "at"
(6) "t"

Output 2: When string Input = The Cat
Substring list printed as an ArrayList : 
[T, Th, The, The , The C, The Ca, The Cat, h, he, he , he C, he Ca, he Cat, e, e , e C, e Ca, e Cat,  ,  C,  Ca,  Cat, C, Ca, Cat, a, at, t]


All substrings printed 1 per line : 
(1) "T"
(2) "Th"
(3) "The"
(4) "The "
(5) "The C"
(6) "The Ca"
(7) "The Cat"
(8) "h"
(9) "he"
(10) "he "
(11) "he C"
(12) "he Ca"
(13) "he Cat"
(14) "e"
(15) "e "
(16) "e C"
(17) "e Ca"
(18) "e Cat"
(19) " "
(20) " C"
(21) " Ca"
(22) " Cat"
(23) "C"
(24) "Ca"
(25) "Cat"
(26) "a"
(27) "at"
(28) "t"

sagar0719kumar
Java-String-Programs
Java
Java Programs
Java
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