Java Programs›Strings›Remove Digits from a String

Remove Digits from a String in Java

beginner· Strings · String Manipulation

Problem

A digit is any of the characters 0 through 9 that can appear inside a string alongside letters and symbols.

Given a string, remove every digit it contains.

Input

Order66Confirmed42

Output

OrderConfirmed

Java Program

Java

public class RemoveDigits {
    public static void main(String[] args) {
        String str = "Order66Confirmed42";
        StringBuilder result = new StringBuilder();
        for (char c : str.toCharArray()) {
            if (!Character.isDigit(c)) result.append(c); // skip digits entirely
        }
        System.out.println(result.toString());
    }
}

▶ Run Code

Output

OrderConfirmed

Core Logic

Keeping every character that isn't a digit, one pass through the string, filters out the digits and leaves everything else in place.

How It Works

1A for-each loop visits each character of the string in turn.
2Character.isDigit(c) checks whether the current character is one of 0 through 9.
3Characters that fail the check are appended to a StringBuilder; digits are simply skipped.
4The final StringBuilder holds every original character except the digits.

For "Order66Confirmed42", the digits 6, 6, 4, and 2 are skipped, producing "OrderConfirmed".

💡

Key Point: This mirrors the digit-counting program exactly, just appending non-digits to a result instead of incrementing a counter for digits.

Complexity

Time Complexity: O(n)Space Complexity: O(n)

Why: Each character is visited once and the result buffer grows to hold every non-digit character, which can be up to n.

Key Concepts

Character.isDigit()StringBuilderfor-each loop

Approach 2: Java 8

Java

import java.util.stream.Collectors;

public class RemoveDigitsStream {
    public static void main(String[] args) {
        String str = "Order66Confirmed42";
        // Keeps every character that isn't a digit, then joins them back into a String
        String result = str.chars()
            .filter(c -> !Character.isDigit(c))
            .mapToObj(c -> String.valueOf((char) c))
            .collect(Collectors.joining());
        System.out.println(result);
    }
}

▶ Run Code

Output

OrderConfirmed

Core Logic

The same is-not-a-digit check can filter a stream of character codes, then join what's left back into a string.

How It Works

1str.chars() returns an IntStream of the string's character codes.
2.filter(c -> !Character.isDigit(c)) keeps only the codes that are NOT a digit.
3.mapToObj(c -> String.valueOf((char) c)) converts each surviving code back into a one-character String.
4.collect(Collectors.joining()) concatenates them all back into a single result string.

Filtering "Order66Confirmed42" drops every digit, and joining what's left reassembles "OrderConfirmed".

💡

Key Point: Negating Character::isDigit with ! flips the same check the loop version uses directly — streams just change how it's applied.

Complexity

Time Complexity: O(n)Space Complexity: O(n)

Why: The stream still visits every character once, and Collectors.joining() builds a result string holding every non-digit character.

Key Concepts

Streamchars()filter()Collectors.joining()

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