Remove all non alphabetic characters from a String array in java

Question

I'm trying to write a method that removes all non alphabetic characters from a Java String[] and then convert the String to an lower case string. I've tried using regular expression to replace the occurence of all non alphabetic characters by "" .However, the output that I am getting is not able to do so. Here is the code

static String[] inputValidator(String[] line) {
    for(int i = 0; i < line.length; i++) {
       line[i].replaceAll("[^a-zA-Z]", "");
       line[i].toLowerCase();
    }
    return line;
}

However if I try to supply an input that has non alphabets (say - or .) the output also consists of them, as they are not removed.

Example Input

A dog is an animal. Animals are not people.

Output that I'm getting

A
dog
is
an
animal.
Animals
are
not
people.

Output that is expected

a
dog
is
an
animal
animals
are
not
people

Here is a sample run to check the method ideone.com/XOugF

hytriutucx
– hytriutucx

2012-06-22 03:24:49 +00:00
Commented Jun 22, 2012 at 3:24 — hytriutucx
– hytriutucx, Commented Jun 22, 2012 at 3:24

Community · Accepted Answer · 2017-05-23 11:45:34Z

50

The problem is your changes are not being stored because Strings are immutable. Each of the method calls is returning a new String representing the change, with the current String staying the same. You just need to store the returned String back into the array.

line[i] = line[i].replaceAll("[^a-zA-Z]", "");
line[i] = line[i].toLowerCase();

Because the each method is returning a String you can chain your method calls together. This will perform the second method call on the result of the first, allowing you to do both actions in one line.

line[i] = line[i].replaceAll("[^a-zA-Z]", "").toLowerCase();

edited May 23, 2017 at 11:45

CommunityBot

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answered Jun 22, 2012 at 3:24

n00begon

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Comments

paulsm4 · Accepted Answer · 2012-06-22 03:25:39Z

7

You need to assign the result of your regex back to lines[i].

for ( int i = 0; i < line.length; i++) {
  line[i] = line[i].replaceAll("[^a-zA-Z]", "").toLowerCase();
}

answered Jun 22, 2012 at 3:25

paulsm4

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Comments

Andrew Barber · Accepted Answer · 2014-08-11 04:30:22Z

4

As it already answered , just thought of sharing one more way that was not mentioned here >

 str = str.replaceAll("\\P{Alnum}", "").toLowerCase();

edited Aug 11, 2014 at 4:30

Andrew Barber

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answered Aug 6, 2013 at 12:20

saurav

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1 Comment

Cornelius Dol Over a year ago

Though this is wider than just the latin letters matched by the OPs code; that may or may not be what is needed.

Sean F · Accepted Answer · 2012-06-22 03:24:30Z

3

It doesn't work because strings are immutable, you need to set a value e.g.

line[i] = line[i].toLowerCase();

answered Jun 22, 2012 at 3:24

Sean F

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2 Comments

DJ. Over a year ago

Sean, you missed the replaceAll call there.

Sean F Over a year ago

i was going to edit it in but once i submitted and 3 other responses existed saying the same thing i didnt see the point.

nhahtdh · Accepted Answer · 2012-06-22 03:24:39Z

3

You must reassign the result of toLowerCase() and replaceAll() back to line[i], since Java String is immutable (its internal value never changes, and the methods in String class will return a new String object instead of modifying the String object).

answered Jun 22, 2012 at 3:24

nhahtdh

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Comments

Pankaj Tungaria · Accepted Answer · 2019-12-01 06:29:24Z

2

Here is working method

 String name = "Joy.78@,+~'{/>";
 String[] stringArray = name.split("\\W+");
 StringBuilder result = new StringBuilder();
   for (int i = 0; i < stringArray.length; i++) {
    result.append(stringArray[i]);
   }
   String nameNew = result.toString();
    nameNew.toLowerCase();

answered Dec 1, 2019 at 6:29

Pankaj Tungaria

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Comments

algorowara · Accepted Answer · 2012-06-22 03:36:55Z

1

A cool (but slightly cumbersome, if you don't like casting) way of doing what you want to do is go through the entire string, index by index, casting each result from String.charAt(index) to (byte), and then checking to see if that byte is either a) in the numeric range of lower-case alphabetic characters (a = 97 to z = 122), in which case cast it back to char and add it to a String, array, or what-have-you, or b) in the numeric range of upper-case alphabetic characters (A = 65 to Z = 90), in which case add 32 (A + 22 = 65 + 32 = 97 = a) and cast that to char and add it in. If it is in neither of those ranges, simply discard it.

answered Jun 22, 2012 at 3:36

algorowara

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Comments

Alex - GlassEditor.com · Accepted Answer · 2018-09-19 06:51:28Z

1

You can also use Arrays.setAll for this:

Arrays.setAll(array, i -> array[i].replaceAll("[^a-zA-Z]", "").toLowerCase());

answered Sep 19, 2018 at 6:51

Alex - GlassEditor.com

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Comments

Akshay kaler · Accepted Answer · 2021-06-07 03:50:06Z

0

public static void solve(String line){

    // trim to remove unwanted spaces
    line= line.trim();

    String[] split = line.split("\\W+");

    // print using for-each
    for (String s : split) {
        System.out.println(s);
    }

answered Jun 7, 2021 at 3:50

Akshay kaler

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