我如何使循环停止在Java中重复

Question

I'm a beginner in Java and I have to write a program that allows the user to enter in words, then the program returns the word backwards until the user writes "stop". Every time the user enters a word, java outputs it backwards plus the previous word which is outputted and I don't want that. For example, if I put input pots it outputs, stop if I print cat it outputs potstac How can I just get java to just output the words backwards without adding it on to the prior words For example, i want to input in pots it should output, stop i want to print cat it should output, tac

import java.util.*;
public class javapdf2413 {
    public static void main (String [] args) {
        Scanner in = new Scanner (System.in);

        String wordEntered = "";
        String backWords = "";

        do {
            System.out.println("Enter in a word");
            wordEntered = in.next();
            for (int i = wordEntered.length()-1; i>=0; i--) {
                backWords = backWords + wordEntered.charAt(i);
            }
            System.out.println(backWords);

        }while(!wordEntered.equals("stop"));
    }

}

Answer 1

You'll need to set backWords back to an empty string at the beginning of the do loop. If you don't it will just concatenate onto the end of the previous string - which is what you said is happening. Setting it back to "" at the beginning of the loop body will essentially "reset" it for the next word.

Like this:

do {
    backWords = "";
    System.out.println("Enter in a word");
    wordEntered = in.next();
    for (int i = wordEntered.length()-1; i>=0; i--) {
        backWords = backWords + wordEntered.charAt(i);
    }
    System.out.println(backWords);

}while(!wordEntered.equals("stop"));

Answer 2

Try to do this with while loop

import java.util.Scanner;

public class TestRun {

    public static void main(String args[]) {

        Scanner in = new Scanner(System.in);

        String wordEntered = "";
        String backWords = "";

        while (true) {
            System.out.println("Enter in a word");
            wordEntered = in.next();

            if (wordEntered.equals("stop")) {
                break;
            } else {
                for (int i = wordEntered.length() - 1; i >= 0; i--) {
                    backWords = backWords + wordEntered.charAt(i);
                }
                System.out.println(backWords);
                backWords = "" ;
            }

        }

    }

}

Answer 3

Just initialize your variables inside your do loop

String wordEntered;
String backWords;

            do {
              wordEntered = "";
              backWords = "";
                System.out.println("Enter in a word");
                wordEntered = in.next();
                for (int i = wordEntered.length()-1; i>=0; i--) {
                    backWords = backWords + wordEntered.charAt(i);
                }
                System.out.println(backWords);

            }while(!wordEntered.equals("stop"));

Answer 4

Just beware - Strings are immutable objects. Use it with right use case and approach. Try to use StringBuilder for non concurrent code as much as possible where ever you can.