Is there any other way to remove all whitespaces in a string?

问题

I have a programming homework. It says that I need to reverse the string first, then change it to uppercase and then remove all the whitespaces. I actually did it, but our professor didn't say anything about using replaceAll() method. Is there any other way to do it beside replaceAll()?

Here is my code:

public static void main(String[] args) {
    String line = "the quick brown fox";
    String reverse = "";

    for (int i = line.length() - 1; i >= 0; i--) {
        reverse = reverse + line.charAt(i);
    }
    System.out.println(reverse.toUpperCase().replaceAll("\\s", ""));

}

回答1:

You can check each character in turn using Character.isWhitespace. Additionally, it is generally better to use a StringBuilder when concatenating inside a loop.

public static void main(String[] args) {
    String line = "the quick brown fox";
    StringBuilder sb = new StringBuilder(line.length());

    for (int i = line.length() - 1; i >= 0; i--) {
        char c = line.charAt(i);
        if(!Character.isWhitespace(c)) sb.append(Character.toUpperCase(c));
    }
    System.out.println(sb);
}

回答2:

@Khelwood's answer as code:

public static void main(String[] args) {
    String line = "the quick brown fox";
    String reverse = "";

    for (int i = line.length() - 1; i >= 0; i--) {
        char currentChar = line.charAt(i);
        if (currentChar != ' ') {
            reverse += currentChar;
        }
    }
    System.out.println(reverse.toUpperCase());

}

回答3:

Even without using replaceAll(), it’s still a one-liner:

String reverse = new StringBuilder(line).reverse().toString().toUpperCase().replace(" ", "");

回答4:

Character#isWhitespace

Initialize a StringBuilder object and iterate through each character of the uppercased string. While iterating, use Character#isWhitespace to check if the character is a whitespace character. If not, append the character to the StringBuilder object. After the loop is finished, the StringBuilder object will have all characters except the whitespace characters.

public class Main {
    public static void main(String[] args) {
        String line = "the quick brown fox";
        String reverse = "";

        for (int i = line.length() - 1; i >= 0; i--) {
            reverse = reverse + line.charAt(i);
        }
        String upperCased = reverse.toUpperCase();
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < upperCased.length(); i++) {
            char ch = upperCased.charAt(i);
            if (!Character.isWhitespace(ch)) {
                sb.append(ch);
            }
        }

        System.out.println("The given string: " + line);
        System.out.println("The reverse of the given string: " + reverse);
        System.out.println("The reverse of the given string in UPPER case: " + upperCased);
        System.out.println("After removing all space from the reverse of the given string in UPPER case: " + sb);
    }
}

Output:

The given string: the quick brown fox
The reverse of the given string: xof nworb kciuq eht
The reverse of the given string in UPPER case: XOF NWORB KCIUQ EHT
After removing all space from the reverse of the given string in UPPER case: XOFNWORBKCIUQEHT

Note:

If you want to convert sb to a String, use sb.toString().
You can use String instead of StringBuilder but I recommend you use StringBuilder instead of String for such a case because repeated string concatenation in a loop creates additional as many instances of String as the number of concatenation. Check this discussion to learn more about it.

回答5:

You can use String.codePoints method to iterate over int values of the characters of this string, to reverse their order, change to uppercase and remove whitespaces:

String line = "the quick brown fox";

String reverse = line
        // return IntStream
        .codePoints()
        // return Stream<Character>
        .mapToObj(ch -> (char) ch)
        // reverse the order
        // of characters once
        .sorted((ch1, ch2) -> -1)
        // change to uppercase
        .map(Character::toUpperCase)
        // remove whitespaces
        .filter(ch -> !Character.isWhitespace(ch))
        // return Stream<String>
        .map(String::valueOf)
        // join strings with
        // characters back
        // to a single string
        .collect(Collectors.joining());

System.out.println(reverse); // XOFNWORBKCIUQEHT

^{See also: Is there a way to reverse specific arrays in a multidimensional array?}

回答6:

to strictly follow the professors description (and intentions?):

public static void main(String[] args) {
    String line = "the quick brown fox";

    String reverse = "";
    for (int i = line.length() - 1; i >= 0; i--) {
        reverse = reverse + line.charAt(i);
    }

    String upperCase = reverse.toUpperCase();

    String noSpaces = "";
    for (int i = 0; i < upperCase.length(); i++) {
        char ch = upperCase.charAt(i);
        if (!Character.isWhitespace(ch)) {
            noSpaces = noSpaces + ch;  // or noSpaces += ch;
        }
    }

    System.out.println(noSpaces);
}

Note 1: this can all be done with one loop, but that would not match the description (or no (user)loop at all?).

_{Note 2: the use of StringBuilder is not needed anymore (when using an actual Java version (>= 11)) - actually I believe it is more efficient not to use it, the compiler does better job (see StringConcatFactory)}

_{Note 3: if allowed to use StringBuilder, it also has a reverse method}

Note 4: be aware (for future) that replaceAll() works with regular expression, very powerful, but kind of overkill to just replace a char - replace() would be more moderate

回答7:

Here are two ways. The first uses a standard loop.

String line = "the quick brown fox";
StringBuilder sb = new StringBuilder();
for (int i = line.length() - 1; i >= 0; i--) {
    char ch;
    if ((ch = line.charAt(i)) != ' ') {
        sb.append(Character.toUpperCase(ch));
    }
}
System.out.println(sb.toString());

Prints

XOFNWORBKCIUQEHT

The second makes use of StringBuilder and replaceAll. And regardless, you should ask your professor since nothing was overtly forbidden.

String str = new StringBuilder("the quick brown fox")
        .reverse().toString().replaceAll("\\s+", "").toUpperCase();

System.out.println(str);

Also prints

XOFNWORBKCIUQEHT

回答8:

If you do not need to store the reversed line, you can also just iterate it backwards and print the character immediately.

public static void main(String[] args) {
    String line = "the quick brown fox";
    for (char c : line.toUpperCase().toCharArray()) {
        if (!Character.isWhitespace(c)) {
            System.out.print(c);
        }
    }
}

来源：https://stackoverflow.com/questions/65374534/is-there-any-other-way-to-remove-all-whitespaces-in-a-string

标签

java

string

replace