如何在 Java 字符串中替换一种以上的字符

Question

newbie here. Any help with this problem would be appreciated:

You are given a String variable called data that contain letters and spaces only. Write the Java class to print a modified version of the String where all lowercase letters are replaced by ? and all whitespaces are replaced by + . An example is shown below: I Like Java becomes I+L???+J??? .

What I have so far:

public static void main (String[] args) {
    Scanner input = new Scanner(System.in);
    String data;

    //prompt
    System.out.println("Enter a sentence: ");

    //input
    data = input.nextLine();
    for (int i = 0; i < data.length(); i++) {
        if (Character.isWhitespace(data.charAt(i))) {
            data.replace("", "+");

            if (Character.isLowerCase(data.charAt(i))) {
                data.replace(i, i++, ); //not sure what to include here
            }
        } else {
            System.out.print(data);
        }
    }
}

any suggestions would be appreciated.

Answer 1

Firstly, you are trying to make changes to String object which is immutable. Simple way to achieve what you want is convert string to character array and loop over array items:

Scanner input = new Scanner(System.in);
String data;

//prompt
System.out.println("Enter a sentence: ");

//input
data = input.nextLine();

char[] dataArray = data.toCharArray();

for (int i = 0; i < dataArray.length; i++) {
    if (Character.isWhitespace(dataArray[i])) {
        dataArray[i] = '+';
    } else if (Character.isLowerCase(dataArray[i])) {
        dataArray[i] = '?';
    }
}

System.out.print(dataArray);

Answer 2

See the below code and figure out what's wrong in your code. To include multiple regex put the char within square brackets:

import java.util.Scanner;

public class mainClass {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter a sentence: ");
        String data = input.nextLine();

        String one = data.replaceAll(" ", "+");
        String two = one.replaceAll("[a-z]", "?");
        System.out.println(two);
    }
}

Answer 3

You can do it in two steps by chaining String#replaceAll . In the first step, replace the regex, [az] , with ? . The regex, [az] means a character from a to z .

public class Main {
    public static void main(String[] args) {
        String str = "I Like Java";
        str = str.replaceAll("[a-z]", "?").replaceAll("\\s+", "+");
        System.out.println(str);
    }
}

Output:

I+L???+J???

Alternatively , you can use a StringBuilder to build the desired string. Instead of using a StringBuilder variable, you can use String variable but I recommend you use StringBuilder for such cases . The logic of building the desired string is simple:

Loop through all characters of the string and check if the character is a lowercase letter. If yes, append ? to the StringBuilder instance else if the character is whitespace, append + to the StringBuilder instance else append the character to the StringBuilder instance as it is.

Demo:

public class Main {
    public static void main(String[] args) {
        String str = "I Like Java";
        StringBuilder sb = new StringBuilder();
        int len = str.length();
        for (int i = 0; i < len; i++) {
            char ch = str.charAt(i);
            if (Character.isLowerCase(ch)) {
                sb.append('?');
            } else if (Character.isWhitespace(ch)) {
                sb.append('+');
            } else {
                sb.append(ch);
            }
        }

        // Assign the result to str
        str = sb.toString();

        // Display str
        System.out.println(str);
    }
}

Output:

I+L???+J???

---

If the requirement states:

1. The first character of each word is a letter (uppercase or lowercase) which needs to be left as it is.
2. Second character onwards can be any word character which needs to be replaced with ? .
3. All whitespace characters of the string need to be replaced with + .

you can do it as follows:

Like the earlier solution, chain String#replaceAll for two steps. In the first step, replace the regex, (?<=\\p{L})\\w , with ? . The regex, (?<=\\p{L})\\w means:

1. \\w specifies a word character .
2. (?<=\\p{L}) specifies a positive lookbeghind for a letter ie \\p{L} .

In the second step, simply replace one or more whitespace characters ie \\s+ with + .

Demo:

public class Main {
    public static void main(String[] args) {
        String str = "I like Java";
        str = str.replaceAll("(?<=\\p{L})\\w", "?").replaceAll("\\s+", "+");
        System.out.println(str);
    }
}

Output:

I+l???+J???

Alternatively , again like the earlier solution you can use a StringBuilder to build the desired string. Loop through all characters of the string and check if the character is a letter. If yes, append it to the StringBuilder instance and then loop through the remaining characters until all characters are exhausted or a space character is encountered. If a whitespace character is encountered, append + to the StringBuilder instance else append ? to it.

Demo:

public class Main {
    public static void main(String[] args) {
        String str = "I like Java";
        StringBuilder sb = new StringBuilder();
        int len = str.length();
        for (int i = 0; i < len; i++) {
            char ch = str.charAt(i++);
            if (Character.isLetter(ch)) {
                sb.append(ch);
                while (i < len && !Character.isWhitespace(ch = str.charAt(i))) {
                    sb.append('?');
                    i++;
                }
                if (Character.isWhitespace(ch)) {
                    sb.append('+');
                }
            }
        }

        // Assign the result to str
        str = sb.toString();

        // Display str
        System.out.println(str);
    }
}

Output:

I+l???+J???

Answer 4

package com.company;

import java.util.*;

public class dat {
    public static void main(String[] args) {
        System.out.println("enter the string:");
        Scanner ss = new Scanner(System.in);
        String data = ss.nextLine();
        for (int i = 0; i < data.length(); i++) {
            char ch = data.charAt(i);
            if (Character.isWhitespace(ch))
                System.out.print("+");
            else if (Character.isLowerCase(ch))
                System.out.print("?");
            else
                System.out.print(ch);
        }
    }
}

enter the string:

i Love YouU
?+L???+Y??U

Answer 5

You can use String.codePoints method to get a stream over int values of characters of this string, and process them:

private static String replaceCharacters(String str) {
    return str.codePoints()
            .map(ch -> {
                if (Character.isLowerCase(ch))
                    return '?';
                if (Character.isWhitespace(ch))
                    return '+';
                return ch;
            })
            .mapToObj(Character::toString)
            .collect(Collectors.joining());
}

public static void main(String[] args) {
    System.out.println(replaceCharacters("Lorem ipsum")); // L????+?????
    System.out.println(replaceCharacters("I Like Java")); // I+L???+J???
}

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^{See also: Replace non ASCII character from string}