How can we check if specific string occurs multiple times in another string in Java?

You can find whether a String contains a specified sequence of characters using any of the methods −
The indexOf() method − The indexOf() method of the String class accepts a string value and finds the (starting) index of it in the current String and returns it. This method returns -1 if it doesn’t find the given string in the current one.
The indexOf() method − The indexOf() method of the String class accepts a string value and finds the (starting) index of it in the current String and returns it. This method returns -1 if it doesn’t find the given string in the current one.
The contains() method − The contains a () method of the String class accepts a sequence of characters value and verifies whether it exists in the current String. If found it returns true else it returns false.
The contains() method − The contains a () method of the String class accepts a sequence of characters value and verifies whether it exists in the current String. If found it returns true else it returns false.
In addition to these, you can also use the Split() method of the String class. This method accepts a String value representing a delimiter, splits the current String based on the given delimiter and returns a String array containing tokens of the String.
You can split the string into an array of words using this method and compare each word with the required word manually.
Following Java example reads the contents of a file into a String, accepts a word from the user and prints the number of times the given word occurred in the String (file).
 Live Demo
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class StringOccurrence {
   public static String fileToString(String filePath){
      Scanner sc = null;
      String input = null;
      StringBuffer sb = null;
      try {
         sc = new Scanner(new File(filePath));
         sb = new StringBuffer();
         while (sc.hasNextLine()) {
            input = sc.nextLine();
            sb.append(" "+input);
         }
      }
      catch(Exception ex) {
         ex.toString();
      }
      System.out.println("Contents of the file: ");
      System.out.println(sb);
      return sb.toString();
   }
   public static void main(String args[]) throws FileNotFoundException {
      //Reading the word to be found from the user
      String filePath = "D://sampleData.txt";
      Scanner sc = new Scanner(System.in);
      System.out.println("Enter the word to be found");
      String word = sc.next();
      boolean flag = false;
      int count = 0;
      String text = fileToString(filePath);
      String textArray[] = text.split(" ");
      for(int i=0; i<textArray.length; i++) {
         if(textArray[i].equals(word)) {
            flag = true;
            count = count+1;
         }
      }
      if(flag) {
         System.out.println("Number of occurrences is: "+count);
      } else {
         System.out.println("File does not contain the specified word");
      }
   }
}
Enter the word to be found
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Contents of the file:
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Number of occurrences is: 4