How to print several strings backwards in Java

问题

I am trying to take a file full of strings, read it, then print out a few things:

The string
The string backwards AND uppercase
The string length

There are a few more things, however I haven't even gotten to that point and do not want to ask anyone to write the code entirely for me. After messing around with it for a while, I have it almost completed (I believe, save for a few areas).

The piece that is tripping me up is the backwards word. We are required to put our output neatly into columns using prinf, but I cannot do this if I read each char at a time. So I tried setting a String backwardsWord = ""; and adding each character.

This is the piece that is tripping me up:

for(int i = upperCaseWord.length() - 1; i >= 0; i--)
{
    backwardsWord += (upperCaseWord.charAt(i) + "");
}

My issue is that when I print it, the first word works properly. However, each word after that is added to the previous word.

For example: if I am printing cat, dog, and rat backwards, it shows

TAC

TACGOD

TACGODTAR

I obviously want it to read

TAC

GOD

TAR

Any help would be appreciated.

回答1:

It looks like your variable backwardsWord is always appending a character without being reset between words. The simplest fix is to clear the backwardsWord just before your loop by setting it to empty string.

backwardsWord = ""; //Clear any existing characters from backwardsWord

for(int i = upperCaseWord.length() - 1; i >= 0; i--)
{
    backwardsWord += (upperCaseWord.charAt(i) + "");
}

If you are building up a String one character at a time you will be using a lot of memory because Java Strings are immutable.

To do this more efficiently use a StringBuilder instead. This is made for building up characters like what you are doing. Once you have finished you can use the toString method to get the String out.

StringBuilder builder = new StringBuilder(); //Creates the String builder for storing the characters
for(int i = upperCaseWord.length() - 1; i >= 0; i--)
{
    builder.append(upperCaseWord.charAt(i)); //Append the characters one at a time 
}
backwardsWord = builder.toString(); //Store the finished string in your existing variable

This has the added benefit of resetting the backwardsWord each time.

Finally, since your goal is to get the String in reverse we can actually do it without a loop at all as shown in this answer

backwardsWord = new StringBuilder(upperCaseWord).reverse().toString()

This creates a new StringBuilder with the characters from upperCaseWord, reverses the characters then stores the final string in backwardsWord

回答2:

Where are you declaring the String backwardsWord?

If you don't clear it between words then the memory space allocated to that string will still contain the previously added characters.

Make sure you are tossing in a backwardsWord = ""; in between words to reset it's value and that should fix your problem.

Without seeing more of your code I can't tell you exactly where to put it.

回答3:

This should do the job ->

class ReverseWordsInString{
public static String reverse(String s1){
        int l = s1.length();
        if (l>1)
                return(s1.substring(l-1) + reverse(s1.substring(0,l-1)));
        else
                return(s1.substring(0));
  }
public static void main(String[] args){
        String st = "Cat Dog Rat";
        String r = "";
        for (String word : st.split(" "))
                r += " "+ reverse(word.toUpperCase());
        System.out.println("Reversed words in the given string: "+r.trim());
  }
}

来源：https://stackoverflow.com/questions/19016446/how-to-print-several-strings-backwards-in-java

标签

java

string

for-loop

reverse