Split a String into a Number of Substrings in Java

A substring is a contiguous sequence of characters within a string. Every non-empty string is a substring of itself. In this article, we will learn how to find all possible non-empty substrings of a given string.

• Define a substring as a contiguous sequence of characters from the original string.
• Clearly state that the program generates non-empty substrings.

Illustration:

Input: bat

Output: b
ba
bat
a
at
t

For a string of length n, the total number of non-empty substrings is:

n * (n + 1) / 2

Approach

• Traverse the string using an outer loop to select the starting index.
• Use an inner loop to select the ending index.
• Generate each substring using the substring() method.
• Store each substring in an ArrayList.
• Print all the generated substrings.

import java.util.ArrayList;

public class Geeks {

    // Method to find all substrings
    static ArrayList<String> findSubstrings(String str) {

        ArrayList<String> substrings = new ArrayList<>();

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

            for (int j = i + 1; j <= str.length(); j++) {

                // Add substring from index i to j - 1
                substrings.add(str.substring(i, j));
            }
        }

        return substrings;
    }

    public static void main(String[] args) {

        String str = "The Cat";

        ArrayList<String> substrings = findSubstrings(str);

        System.out.println("All substrings:");

        for (String substring : substrings) {
            System.out.println(substring);
        }
    }
}

All substrings:
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

Explanation

• The outer loop selects the starting index of each substring.
• The inner loop selects the ending index.
• substring(i, j) extracts characters from index i to j - 1.
• Each generated substring is added to the ArrayList.
• For "The Cat", the program generates 28 non-empty substrings.