Frequently Asked Java Program 22: Java Program to Trim Whitespace From String Without Using Trim Method

Hello Folks,

This interview question was asked in Deloitte. 

Write a java program to Trim a given string without using inbuilt trim() method of String Class in Java.

“trim()” method of String class trims leading and trailing whitespace/s of given string. It does not remove whitespace between words. We need to write logic to do so.

Logic step by step:

1. We need to find first index of non space char in given string from beginning. Say it First.
2. We need to find first index of non space char in given string from end. Say it Last.
3. Return a substring indexing from First till Last.

Detailed Explanation:

1. Assume first char of given string is a non space char and set starting index of non space char as zero. Now check if it is really a non space char. If it it, finalize starting index as zero else increment index by one and repeat the same till you get a non space char.
2. Assume last char of given string is a non space char and set last index of non space char as (Length of String-1). Now check if it is really a non space char. If it it, finalize end index as (Length of String-1) else decrement index by one and repeat the same till you get a non space char.
3. Once Starting and Ending index are finalized, get the substring.

Java Program:

package StringPrograms;

import java.util.Scanner;

public class TrimSpacesWithoutTrimMethod {

        public static String trimSpace(String str) {

                // Assume 0th index is non-space character
                int startNonSpaceIndex = 0;

                // Assume last index is non-space character
                int endNonSpaceIndex = str.length()-1;

                // Store length in a variable
                int strLength = str.length();

                // Convert string into char array
                char[] val = str.toCharArray();

                // Increment startNonSpaceIndex by one until you really find a non space char
                while (startNonSpaceIndex < strLength && val[startNonSpaceIndex] == ' ') {
                        startNonSpaceIndex++;
                }

                // Decrement endNonSpaceIndex by one until you really find a non space char
                // Since we know starting index of a non space char, so we should not exceed
                // that which
                // is taking care by (startNonSpaceIndex < endNonSpaceIndex)
                while (startNonSpaceIndex < endNonSpaceIndex && val[endNonSpaceIndex] == ' ') {
                        endNonSpaceIndex--;
                }

                // Now you have actual starting and ending index of non space char in given
                // string.
                return str.substring(startNonSpaceIndex, endNonSpaceIndex+1);
        }

        public static void main(String[] args) {

                // User input to trim spaces
                Scanner sc = new Scanner(System.in);
                System.out.println("Please enter the string to trim spaces:");

                String userInput = sc.nextLine();

                sc.close();

                System.out.println("You entered with spaces: \"" + userInput+"\"");
                
                System.out.println("String after trimming space: \""+trimSpace(userInput) +"\"");
        }
}

Output:

[java] Please enter the string to trim spaces: Make Selenium Easy You entered with spaces: ” Make Selenium Easy ” String after trimming space: “Make Selenium Easy” ================================================= Please enter the string to trim spaces: Make Selenium Easy You entered with spaces: ” Make Selenium Easy ” String after trimming space: “Make Selenium Easy” =================================================

[/java]