How to find the substrings of a given string?

package pack1;

import java.util.Set;

public interface SubstrsIntf {
	
	/* Define the Functional interface with SAM 'ParseTheWord' */
	public Set<String> ParseTheWord(String inputWord);

	/* Define the Static method 'displayMsg' */
	public static void displayMsg(Set<String> finalSubsetStrs, String inpStrVal) {
		System.out.println("All the unique substrings from the given String="+inpStrVal+" are below");
	    System.out.println(finalSubsetStrs);
	}
}

package pack1;

import java.util.HashSet;
import java.util.Optional;
import java.util.Set;
import java.util.logging.Logger;

class StringInput {

	private String inpStrVal;

	/* Declare the logger object for the class to display the log messages */
	static Logger logger = Logger.getLogger(StringInput.class.getName());

	public boolean validateInputs(String inpWord) {

		/* Fetch the class object's name from which this method is called */
		String cName = Thread.currentThread().getStackTrace()[2].getClassName();
		String mName = "validateInputs()";
		logger.info("This method '" + mName + "' called from the Class '" + cName + "'");

		/* Validating the function parameters using Optional String data type */
		Optional<String> strInput = Optional.ofNullable(inpWord);

		/*
		 * Fetch the value of the Optional String using 'isPresent' condition check. 
		 * If the value is not null, then use the 'get' method otherwise simply
		 * return 'false' to stop the program execution without proceeding further.
		 */
		if (strInput.isPresent()) {
			setInpStrVal(strInput.get());
		} else {
			return false;
		}
		logger.info("The provided Input validated Successfully");
		return true;
	}
	
	/* Define getter and setters for inpStrVal String variable */
	public String getInpStrVal() {
		return inpStrVal;
	}

	public void setInpStrVal(String inpStrVal) {
		this.inpStrVal = inpStrVal;
	}	
}

class Substrs_Using_String extends StringInput implements SubstrsIntf {

	public Set<String> ParseTheWord(String inpWord) {

		/* Fetch the class object's name from which this method is called */
		String cName = Thread.currentThread().getStackTrace()[2].getClassName();
		String mName = "ParseTheWord";
		logger.info("This method '" + mName + "' called from the Class '" + cName + "'");

		/* Define a Set of data type Strings */
		Set<String> finalSubsetStrs = new HashSet<String>  ();
	       
		if (validateInputs(inpWord)) {

			int sizeOfSubstr=1,beginIdx=0, endIdx=1;
	         
	        //Iterate the loop until the substring's length is equals with length of the actual string
	        while (sizeOfSubstr <= getInpStrVal().length()) {
	         
	            //Iterate the substring sized loop until the subscript less than or equals the actual length
	            while (beginIdx < getInpStrVal().length() && endIdx <= getInpStrVal().length()) 
	                finalSubsetStrs.add(getInpStrVal().substring(beginIdx++, endIdx++));
	         
	        sizeOfSubstr++; // Increment size of sub string for the next iteration
	        beginIdx=0;
	        endIdx=sizeOfSubstr;
	        }
		} else
			logger.info("The given Input String is null");

		SubstrsIntf.displayMsg(finalSubsetStrs,inpWord);
		return finalSubsetStrs;
	}
}

class Substrs_WithoutUsing_SubstringMethod extends StringInput implements SubstrsIntf {

	public Set<String> ParseTheWord(String inpWord) {

		/* Fetch the class object's name from which this method is called */
		String cName = Thread.currentThread().getStackTrace()[2].getClassName();
		String mName = "ParseTheWord";
		logger.info("This method '" + mName + "' called from the Class '" + cName + "'");

		/* Define a Set of type Strings */
		Set<String> finalSubsetStrs = new HashSet<String>  ();
	       
		if (validateInputs(inpWord)) {

			int sizeOfSubstr=1,beginIdx=0, endIdx=1;
	         
	        //Iterate the loop until the substring's length is equals with length of the actual string
	        while (sizeOfSubstr <= getInpStrVal().length()) {
	         
	            //Iterate the substring sized loop until the subscript less than or equals the actual length
	            while (beginIdx < getInpStrVal().length() && endIdx <= getInpStrVal().length()) 
	                finalSubsetStrs.add(prepSubstr(beginIdx++, endIdx++, getInpStrVal()));
	         
	        sizeOfSubstr++; // Increment size of sub string for the next iteration
	        beginIdx=0;
	        endIdx=sizeOfSubstr;
	        }
		} else
			logger.info("The given Input String is null");

		SubstrsIntf.displayMsg(finalSubsetStrs,inpWord);
		return finalSubsetStrs;
	}

	private static String prepSubstr(int bIdx, int eIdx, String inpWord) {
		 
        StringBuilder formStr=new StringBuilder ();
        for(int i=bIdx;i<=eIdx-1;i++ )
            formStr.append(inpWord.charAt(i));
        return formStr.toString();
    }
}

class Substrs_Using_Lambda extends StringInput {
	
	
	SubstrsIntf ss = ((strVal) -> {
        int sizeOfSubstr = 1, beginIdx = 0, endIdx = 1;
        Set<String> SubsetStrs = new HashSet<String>();

        /* Iterate the loop until the substring's length is equals with length of the
        actual string */
        while (sizeOfSubstr <= strVal.length()) {

            /*Iterate the substring sized loop until the subscript less than or equals the
             actual length */
            while (beginIdx < strVal.length() && endIdx <= strVal.length())
                SubsetStrs.add(strVal.substring(beginIdx++, endIdx++));

            /*
             * Increment size of sub string 'sizeOfSubstr' by 1, reset 'beginIdx' and assign
             * next sized substring to 'endIdx' for the next iteration
             */
            sizeOfSubstr++;
            beginIdx = 0;
            endIdx = sizeOfSubstr;
        }
        return SubsetStrs;
    });

	public Set<String> ParseTheWord(String inpWord) {

		/* Fetch the class object's name from which this method is called */
		String cName = Thread.currentThread().getStackTrace()[2].getClassName();
		String mName = "ParseTheWord";
		logger.info("This method '" + mName + "' called from the Class '" + cName + "'");

		/* Define a Set of type Strings */
		Set<String> finalSubsetStrs = new HashSet<String>  ();
	       
		if (validateInputs(inpWord)) {
			/* Call the Single AbStract Method 'ParseTheWord' of the interface*/
			finalSubsetStrs = ss.ParseTheWord(getInpStrVal());
		} else
			logger.info("The given Input String is null");

		SubstrsIntf.displayMsg(finalSubsetStrs,inpWord);
		return finalSubsetStrs;
	}
}

public class SubstrsJ8 {
	
	public static void main(String args[]) {
		
		/*
		 * create the class object Substr_Using_String, and call the method 'ParseTheWord'
		 */
		Substrs_Using_String SubUStr = new Substrs_Using_String();
		SubUStr.ParseTheWord("TONY");	
		SubUStr.ParseTheWord(null);
		SubUStr.ParseTheWord("");
		/*
		 * create the class object Substrs_WithoutUsing_SubstringMethod, and call the method 'ParseTheWord'
		 */
		Substrs_WithoutUsing_SubstringMethod SubUStrWithout = new Substrs_WithoutUsing_SubstringMethod();
		SubUStrWithout.ParseTheWord("KERR");
		SubUStrWithout.ParseTheWord(null);
		SubUStrWithout.ParseTheWord("");
		/*
		 * create the class object Substrs_Using_Lambda, and call the method 'ParseTheWord'
		 */
		Substrs_Using_Lambda SubUStrUL = new Substrs_Using_Lambda();
		SubUStrUL.ParseTheWord("3qW&$#");
		SubUStrUL.ParseTheWord(null);
		SubUStrUL.ParseTheWord("");
	}
}