How to Extract Digits from a String in Java?

Extracting Digits from a String in Java

Introduction:
In Java, extracting digits from a string can be a common requirement for various data-processing scenarios. This article explores efficient methods to achieve this extraction, leveraging built-in functions and external libraries.

Solution 1: Regular Expression Replacement

One approach is to use the replaceAll() method to replace all non-digits with an empty string. This can be achieved using the following regular expression:

<code class="java">str = str.replaceAll("\D+","");</code>

where str is the input string containing both digits and non-digits. This method removes all characters that are not digits, leaving only the numerical sequence.

Considerations:

This approach is simple to implement and does not require additional libraries. However, it is important to note that this method assumes that the input string contains only ASCII digits. If non-ASCII digits are present, they will not be extracted.

Solution 2: Character Manipulation

Another technique involves iterating through the characters of the input string and manually checking if each character is a digit. If it is, the character is appended to a result string. This can be achieved using the following code:

<code class="java">StringBuilder result = new StringBuilder();
for (char c : str.toCharArray()) {
    if (Character.isDigit(c)) {
        result.append(c);
    }
}</code>

where result is the output string containing the extracted digits.

Considerations:

This approach is more flexible than the regular expression method, as it allows for more complex character processing. It also works well for both ASCII and non-ASCII digits. However, it can be less efficient for very large input strings, as it requires iterating through all characters.

Conclusion:

Extracting digits from a string in Java can be achieved using various methods, each with its own advantages and disadvantages. Regular expression replacement is a simple and efficient solution for straightforward scenarios, while character manipulation provides greater flexibility and customization for more complex cases.

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