How to reverse each word in a sentence without using reverse method

import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

public class ReverseString {

	public static void main(String[] args) {

		Scanner inpStr = new Scanner(System.in);
		System.out.println("Enter an input sentence");
		String inpLine = inpStr.nextLine();
		if (inpLine.isEmpty() == true) {
			System.out.println("Given string is empty");
		} else {
			String resultStr = "";

			// Split the input sentence into list of words with space as delimiter
			List<String> words = Arrays.asList(inpLine.split("\\s"));
			// System.out.println(words);

			if (isContainsValidWords(words) == false) {
				System.out.println("Invalid input");

			} else {
				// Pass each word to the reverse function which returns the reversed string
				// value
				for (int i = 0; i < words.size(); i++) {
					resultStr = resultStr + ReverseStringMethod(words.get(i)) + " ";
				}
				inpStr.close();
				System.out.println("The output sentence after reversing each word is below");
				System.out.println(resultStr);
			}

		}

	}

	private static boolean isContainsValidWords(List<String> words1) {
		/*
		 * This method checks if every single word in the given string is valid. It goes
		 * through the list of words and uses the method "isValidWord" on each word.
		 * Using a counter variable (validWordCount), if the no. of valid words in the
		 * string is equal to the length of string, it returns true
		 */
		int validWordCount = 0;
		for (int i = 0; i < words1.size(); i++) {
			String tmpStr = words1.get(i);
			if (isValidWord(tmpStr))
				validWordCount++;
		}
		if (validWordCount == words1.size())
			return true;
		else
			return false;
	}

	private static String ReverseStringMethod(String strVar) {
		/*
		 * Using basic logic of storing characters in the reverse order
		 */
		String strRev = "";
		for (int i = strVar.length() - 1; i >= 0; i--)
			strRev = strRev + strVar.charAt(i);
		return strRev;
	}

	public static boolean isValidWord(String s) {
		/*
		 * This method uses regular expressions to first check if the given word
		 * consists of only numbers and then, check if it has any symbols. If it doesn't
		 * only have numbers and doesn't have any symbols, it's a valid word.
		 */
		boolean onlyNumberChecker = s.matches("[0-9]*$") && s.matches("[^a-zA-Z]*$");
		boolean noSymbolChecker = s != null && s.matches("^[a-zA-Z0-9]*$");
		if (onlyNumberChecker == false && noSymbolChecker == true)
			return true;
		else if (onlyNumberChecker)
			return false;
		else
			return false;
	}
}