How to Implement Accurate Version String Comparisons in Java?

How to Compare Version Strings Accurately in Java

Comparing version numbers in Java can be a tricky task, especially when the maximum number of point releases is unknown. While a simple string comparison using compareTo is insufficient, a custom solution is necessary to handle this complexity.

One such solution involves creating a custom Version class that implements the Comparable interface. Here's how it can be done:

public class Version implements Comparable<Version> {

    private String version;

    public final String get() {
        return this.version;
    }

    public Version(String version) {
        if(version == null)
            throw new IllegalArgumentException("Version can not be null");
        if(!version.matches("[0-9]+(\.[0-9]+)*"))
            throw new IllegalArgumentException("Invalid version format");
        this.version = version;
    }

    @Override public int compareTo(Version that) {
        if(that == null)
            return 1;
        String[] thisParts = this.get().split("\.");
        String[] thatParts = that.get().split("\.");
        int length = Math.max(thisParts.length, thatParts.length);
        for(int i = 0; i < length; i++) {
            int thisPart = i < thisParts.length ?
                Integer.parseInt(thisParts[i]) : 0;
            int thatPart = i < thatParts.length ?
                Integer.parseInt(thatParts[i]) : 0;
            if(thisPart < thatPart)
                return -1;
            if(thisPart > thatPart)
                return 1;
        }
        return 0;
    }

    // ...
}

The Version class consists of a constructor that validates the version format and a compareTo method that compares two instances based on their version strings. The compareTo method gracefully handles null values, and for non-null values, it splits the version strings into parts, comparing them one by one.

Using this custom class, comparing version numbers becomes straightforward:

Version a = new Version("1.1");
Version b = new Version("1.1.1");
a.compareTo(b) == -1; // true

This solution reliably handles version comparisons with varying numbers of point releases, ensuring accuracy and consistency.

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