Thread: Loop Character Replacement Issue

Hello, I'm just learning programming and in my Computer Science class have been told to use loops to perform several operations. However I am currently having issues with replacing all white spaces with nothing. Below is my full program and the method I am having this issue with is removeWhitespaces. Any help is greatly appreciated, I just can't figure out what I'm doing wrong as all the console outputs for that portion is the original string I type in.

import java.util.Scanner;
 
 
public class SentenceAnalysis {
 
	public static int countWhitespaces(String sentence){
		boolean isDigit = true;
		int timesSpace = 0;
		char ch;
 
		for(int i = 0; i < sentence.length(); i++){
			ch = sentence.charAt(i);
			if (ch == ' ')
				timesSpace++;
 
		}
		return timesSpace;
	}
 
	public static String removeWhitespaces(String text){
		char ch;
		for(int i = 0; i < text.length(); i++){
			ch = text.charAt(i);
			if (ch == ' '){
				ch = '\0';
			}
			if (ch == '.'){
				ch = '\0';
			}
			if (ch == ','){
				ch = '\0';
			}	
		}
		return text;
	}
 
	public static void main(String[] args) {
		int n = 0;
		Scanner input = new Scanner(System.in);
		String sentence = input.nextLine();
		int result = countWhitespaces(sentence);
		System.out.println("Number of spaces: " + result);
		boolean digits = isNumeric(sentence);
		System.out.println("Has only digits: " + digits);
		String text = removeWhitespaces(sentence);
		System.out.println(text);
 
	}
 
	public static boolean isNumeric(String sentence){
		char ch;
		int timesDigit = 0;
		for(int i = 0; i < sentence.length(); i++){
			ch = sentence.charAt(i);
			boolean isDigit = (ch=='0') || (ch=='1') || (ch=='2') || (ch=='3') || (ch=='4') || (ch=='5') || (ch=='6') || (ch=='7') || (ch=='8') || (ch=='9');
			if (isDigit == true)
				timesDigit++;
 
			}
		if (timesDigit < sentence.length())
			return false;
		else
			return true;
	}
 
}

An interesting question that will require you to see the code differently in order to correct it. To help you make that change in perspective, answer the question, "How does the method removeWhiteSpaces() change the input String object, text?"

Not necessary, but it would enable a better design, are you allowed to use StringBuilder?

Okay so is the problem that when it checks and replaces the value that it is not saving the value after? If so I'm a little confused on how to change it.

The only restrictions are that I have to use loops and the specific method public static String removeWhitespaces(String text)

is the problem that when it checks and replaces the value that it is not saving the value

Pretty much. The only 'value' being changed is ch, and that has no effect on the original String object. So the answer to my question is, "It doesn't."

Another way:

Since Strings are immutable, "changing" a String object actually creates a new one. On the other hand, a StringBuilder can be modified and when complete can be easily converted to a String object using the toString() method.

With that in mind, another possible algorithm is to use a loop that adds each desirable character from the original String object to a StringBuilder object, skipping those that aren't wanted.

There are a few ways to do it. You can convert your String to an array of characters - String#toCharArray. And then you need to iterate over the array and replace char with new value.

char[] chars = "lorem ipsum sit amet".toCharArray();
char newValue = 'X';
for (int i = 0; i < chars.length; i++) {
if (chars[i] == 'm') {
chars[i] = newValue;
}
}
System.out.println(new String (chars)); // loreX ipsuX sit aXet