How can I remove punctuation from input text in Java?

Question

I am trying to get a sentence using input from the user in Java, and i need to make it lowercase and remove all punctuation. Here is my code:

    String[] words = instring.split("\\s+");
    for (int i = 0; i < words.length; i++) {
        words[i] = words[i].toLowerCase();
    }
    String[] wordsout = new String[50];
    Arrays.fill(wordsout,"");
    int e = 0;
    for (int i = 0; i < words.length; i++) {
        if (words[i] != "") {
            wordsout[e] = words[e];
            wordsout[e] = wordsout[e].replaceAll(" ", "");
            e++;
        }
    }
    return wordsout;

I cant seem to find any way to remove all non-letter characters. I have tried using regexes and iterators with no luck. Thanks for any help.

Answer 1

This first removes all non-letter characters, folds to lowercase, then splits the input, doing all the work in a single line:

String[] words = instring.replaceAll("[^a-zA-Z ]", "").toLowerCase().split("\\s+");

Spaces are initially left in the input so the split will still work.

By removing the rubbish characters before splitting, you avoid having to loop through the elements.

Answer 2

You can use following regular expression construct

Punctuation: One of !"#$%&'()*+,-./:;<=>?@[]^_`{|}~

inputString.replaceAll("\\p{Punct}", "");

Answer 3

You may try this:-

Scanner scan = new Scanner(System.in);
System.out.println("Type a sentence and press enter.");
String input = scan.nextLine();
String strippedInput = input.replaceAll("\\W", "");
System.out.println("Your string: " + strippedInput);

[^\w] matches a non-word character, so the above regular expression will match and remove all non-word characters.

Answer 4

If you don't want to use RegEx (which seems highly unnecessary given your problem), perhaps you should try something like this:

public String modified(final String input){
    final StringBuilder builder = new StringBuilder();
    for(final char c : input.toCharArray())
        if(Character.isLetterOrDigit(c))
            builder.append(Character.isLowerCase(c) ? c : Character.toLowerCase(c));
    return builder.toString();
}

It loops through the underlying char[] in the String and only appends the char if it is a letter or digit (filtering out all symbols, which I am assuming is what you are trying to accomplish) and then appends the lower case version of the char .

Answer 5

I don't like to use regex, so here is another simple solution.

public String removePunctuations(String s) {
    String res = "";
    for (Character c : s.toCharArray()) {
        if(Character.isLetterOrDigit(c))
            res += c;
    }
    return res;
}

Note: This will include both Letters and Digits

Answer 6

If your goal is to REMOVE punctuation, then refer to the above. If the goal is to find words, none of the above solutions does that. INPUT: "This. and:that. with'the-other". OUTPUT: ["This", "and", "that", "with", "the", "other"] but what most of these "replaceAll" solutions is actually giving you is: OUTPUT: ["This", "andthat", "withtheother"]