Recursively Search For String In Java

Illustrating searching string recursively in Java and getting it's indexes & also no.of times the string occurred.  This logic is easy and simple. Here is an example program.

 import java.util.*;
 class RecursiveStringSearch
 {
 public static void main(String args[])
 {
 Scanner s=new Scanner(System.in);
 System.out.println("Enter main string");
 String st=s.nextLine();
 System.out.println("Enter search string");
 String se=s.nextLine();
 int idx=-1;
 int i;
 for(i=0;i<st.length();i++)
 {
 idx=st.indexOf(se,i+idx);
 if(idx==-1)break;
 System.out.println("Found at index "+idx);
 }
 System.out.println("Totally found "+i+" times.");
 }
 }

Recursive String Search Output

 
 
 Enter main string
 
 this is a sample test.
 
 Enter search string
 
 is
 
 Found at index 2
 
 Found at index 5
 
 Totally found 2 times.
 

Explaining The Logic

Make the idx=-1 which indicates that the string is not found at first.

int i is for counting the no.of times the string occurred.

Loop till the end of the main string, the string in which the search has to go.

idx=st.indexOf(se,i+idx); which updates the value of idx with the index of the search string in the main string. i+idx is because when the loop updates, the next search has to start after the last index.

if(idx==-1)break; Exit the loop if the string is not found. Whenever the string is not found, the loop is terminated.

i is the value which is nothing but the no.of times the string had occurred in the main string. Because i value will be updated only with the no.of times the string is according to the logic.

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